10/31/11
Happy Halloween!
Such a busy day of tidying up loose ends for momentum in preparation for our exam on Wednesday. B Block conducted a lab investigation on the impulse-momentum theorem, C and F Blocks discussed elastic collisions and E Block discussed the types of collisions in one whole go. For your collisions, be able to describe their basic properties and what happens in therms of conservation of momentum and kinetic energy. Problem solving involves your basic idea of conservation of momentum, with you having to craft a specific formula work with based on the specifics of the problem. Tomorrow, we'll go over homework, walk through the chapter and get ourselves ready for the exam. On Thursday - circular motion!
10/28/11
Collisions!
Today was conservation of momentum or collisions, depending on the block. B and F Block worked on collisions with B Block getting perfectly inelastic, inelastic and elastic collisions in one gulp and F Block getting perfectly inelastic collisions in a small nibble. Collisions are categorized by how well they conserve kinetic energy. Elastics do a great job, perfectly inelastics do a poor job and inelastics are in between. Also, for perfectly inelastic collisions, the objects stick together and move as a unit after the interaction. In truth, most collisions are inelastic in nature, but for our purposes, we'll consider them either perfectly inelastic or elastic and go from there.
C Block worked on their Impulse-Momentum lab. Remember to take care in your calculations of momentum change that the signs for initial and final velocity are correct and used properly in the determination of Δp. We'll go over the lab on Monday, but make sure to consider the items I put on the board when framing your conclusion -what should we have seen for the agreement of impulse and momentum change/sources of error in experiment; how did time and magnitude of force compare for the thin and thick rubber band and how does that play into the impulse-momentum theorem.
E Block discussed the idea of conservation of momentum. Although a collision changes the momentum of each object involved, the total momentum of the system remains the same. We have Newton's 3rd Law of Motion and impulse to thank for this and we examined how momentum conservation played out in different examples from real life. Keep these in mind as you approach problem-solving and setting up proper equations. We'll bring conservation of momentum with us Monday into our discussion of collisions and will see it again when we discuss rotational motion.
C Block worked on their Impulse-Momentum lab. Remember to take care in your calculations of momentum change that the signs for initial and final velocity are correct and used properly in the determination of Δp. We'll go over the lab on Monday, but make sure to consider the items I put on the board when framing your conclusion -what should we have seen for the agreement of impulse and momentum change/sources of error in experiment; how did time and magnitude of force compare for the thin and thick rubber band and how does that play into the impulse-momentum theorem.
E Block discussed the idea of conservation of momentum. Although a collision changes the momentum of each object involved, the total momentum of the system remains the same. We have Newton's 3rd Law of Motion and impulse to thank for this and we examined how momentum conservation played out in different examples from real life. Keep these in mind as you approach problem-solving and setting up proper equations. We'll bring conservation of momentum with us Monday into our discussion of collisions and will see it again when we discuss rotational motion.
10/27/11
Conservation of Momentum and Collisions
E Block reviewed yesterday's lab and then moved into a discussion of momentum and impulse, which was the lab's focus topic. Make sure you can explain each of those ideas, as well as implications of the impulse-momentum theorem. We'll go over your homework problems tomorrow, but they should go pretty quickly since you performed the same calculations for your lab analysis.
B and F Blocks had their discussion of conservation of momentum. Remember that conservation of momentum is a system-based concept. It is absolutely expected that the momentum of individual objects changes after a collision. It is the system's total momentum that remains unchanged. A gain by one is matched by an equal loss in the other. We looked at how conservation of momentum arose from Newton's 3rd Law of Motion and the concept of impulse and how to perform calculations with various conservation of momentum situations. We'll go over those homework items tomorrow before striking out into the different forms of collisions.
C Block spent the period reviewing conservation of momentum and examining perfectly inelastic collisions. For this type of collision, we expect to see a reduction in kinetic energy, although momentum is still conserved system-wide. For these collisions, we assume that the objects stick together and move as a single unit after the interaction and that kinetic energy is lost in the deformation of the objects, as well as though sound and heat due to friction. We'll hit elastic collisions after tomorrow's lab on the impulse-momentum theorem.
For everyone - exam on Wednesday, so start appropriate time and resource management techniques now...
B and F Blocks had their discussion of conservation of momentum. Remember that conservation of momentum is a system-based concept. It is absolutely expected that the momentum of individual objects changes after a collision. It is the system's total momentum that remains unchanged. A gain by one is matched by an equal loss in the other. We looked at how conservation of momentum arose from Newton's 3rd Law of Motion and the concept of impulse and how to perform calculations with various conservation of momentum situations. We'll go over those homework items tomorrow before striking out into the different forms of collisions.
C Block spent the period reviewing conservation of momentum and examining perfectly inelastic collisions. For this type of collision, we expect to see a reduction in kinetic energy, although momentum is still conserved system-wide. For these collisions, we assume that the objects stick together and move as a single unit after the interaction and that kinetic energy is lost in the deformation of the objects, as well as though sound and heat due to friction. We'll hit elastic collisions after tomorrow's lab on the impulse-momentum theorem.
For everyone - exam on Wednesday, so start appropriate time and resource management techniques now...
10/26/11
Moving on With Momentum
B and F Blocks had their introduction to momentum and the impulse-momentum theorem. An object's momentum - the inertia in motion - is affected by the size of the force it experiences and the duration that the force acts on the object. We looked at examples where small forces produced large momentum change (through long time intervals) and where large forces produced small momentum change (through tiny time intervals). Remember that momentum is a vector and inherits the direction piece from velocity. Because of this, it is critical to properly assign and track signs when calculating momentum change.
E Block conducted their impulse-momentum theorem lab, comparing the equivalence of the two for a stiff and loose rubber band. Make careful calculations of momentum change and explain any variations between the measured impulse and the calculated change of momentum. We'll discuss the impulse-momentum theorem tomorrow and use the lab to highlight the discussion.
C Block took a look at conservation of momentum. In a closed system, the total momentum of objects in the system stays the same, regardless of the interactions they experience. However, the momentum of individual objects will change. We looked at how Newton's 3rd Law of Motion and the idea of impulse mandated conservation of momentum for two objects striking each other (the simplest model) and discussed common scenarios encountered in problem solving. Remember that for systems that start at rest (like a cannonball in a cannon), momentum is still conserved once the cannonball is fired. The cannonball and cannon have equal and opposite changes of momentum, which would still sum to a total momentum of zero. We could use that information, then, to calculate the speed of the cannonball or the recoil velocity of the cannon, if necessary. We'll go over your homework problems tomorrow before taking a closer look at the idea of a "collision."
E Block conducted their impulse-momentum theorem lab, comparing the equivalence of the two for a stiff and loose rubber band. Make careful calculations of momentum change and explain any variations between the measured impulse and the calculated change of momentum. We'll discuss the impulse-momentum theorem tomorrow and use the lab to highlight the discussion.
C Block took a look at conservation of momentum. In a closed system, the total momentum of objects in the system stays the same, regardless of the interactions they experience. However, the momentum of individual objects will change. We looked at how Newton's 3rd Law of Motion and the idea of impulse mandated conservation of momentum for two objects striking each other (the simplest model) and discussed common scenarios encountered in problem solving. Remember that for systems that start at rest (like a cannonball in a cannon), momentum is still conserved once the cannonball is fired. The cannonball and cannon have equal and opposite changes of momentum, which would still sum to a total momentum of zero. We could use that information, then, to calculate the speed of the cannonball or the recoil velocity of the cannon, if necessary. We'll go over your homework problems tomorrow before taking a closer look at the idea of a "collision."
10/25/11
Momentum and Impulse
C and F Blocks started their unit on momentum today. B Block had a discussion focusing on momentum, impulse and the impulse-momentum theorem. Momentum, often viewed as the measure of motion, is the product of mass and velocity. Because of the velocity piece, momentum is a vector with the direction matching the direction of the velocity. This becomes very important when working with momentum change. If directions changes from positive to negative (right to left, north to south), you have to be sure to include the proper signs in your calculations. When an object's momentum does change, we would expect that a force was at the root of it, since the piece of momentum that changed was almost certainly the velocity piece. And, since a change of velocity indicates acceleration, we know a force is promoting the momentum change we measure. But, the duration of the applied force also plays a part and that leads to the concept of impulse.
Impulse is the product of force and time interval. The same impulse can exist for two different forces, if the time interval is also different. A 10 Nxs impulse can be achieved through 5N and 2s, 10N and 1s or 1N and 10s. And all of these will produce the same change in momentum of the object. So, it depends on the situation - do you need a small force or a large force - that will set the time you need to apply the force. We discussed the need for follow-through in sports and the science behind safety devices such as air bags and safety nets and will look more at impulse and momentum in lab, as F Block did today. The lab today used a force sensor to directly measure the impulse acting on a moving cart and a motion detector measured the velocity changes produced by the impulse. Make careful calculations of the change of momentum when working on your lab and think about why it does or does not match the measured impulse and how the loose and tight rubber bands compared in changing the motion of the cart.
B and E Blocks took their work and energy exams and will start on momentum and impulse tomorrow.
Impulse is the product of force and time interval. The same impulse can exist for two different forces, if the time interval is also different. A 10 Nxs impulse can be achieved through 5N and 2s, 10N and 1s or 1N and 10s. And all of these will produce the same change in momentum of the object. So, it depends on the situation - do you need a small force or a large force - that will set the time you need to apply the force. We discussed the need for follow-through in sports and the science behind safety devices such as air bags and safety nets and will look more at impulse and momentum in lab, as F Block did today. The lab today used a force sensor to directly measure the impulse acting on a moving cart and a motion detector measured the velocity changes produced by the impulse. Make careful calculations of the change of momentum when working on your lab and think about why it does or does not match the measured impulse and how the loose and tight rubber bands compared in changing the motion of the cart.
B and E Blocks took their work and energy exams and will start on momentum and impulse tomorrow.
10/24/11
The End of Work
C and F Blocks took their work and energy exams today and will start with momentum and impulse tomorrow. F Block will conduct a lab investigation centering on the impulse-momentum theorem. When we started the previous chapter, we said there were some other things one had to consider about an object's change in motion besides the size of the net force - distance through which the force was acting and the duration of the application of the force. We looked at the distance piece with work and add the time piece in this chapter. The impulse-momentum looks at force, time and momentum change, with impulse being defined as the product of net force and time. In Newton's day, force was looked at as the rate of change of momentum, another way of relating the variables. You'll investigate this tomorrow and C Block will discuss it in class.
B and E blocks reviewed Friday's work on power and also the concepts for the chapter in preparation for tomorrow's exam. As for C and F Blocks, we will move into momentum and impulse after our test and the lab that F Block will conduct on Wednesday will investigate the impulse-momentum theorem.
B and E blocks reviewed Friday's work on power and also the concepts for the chapter in preparation for tomorrow's exam. As for C and F Blocks, we will move into momentum and impulse after our test and the lab that F Block will conduct on Wednesday will investigate the impulse-momentum theorem.
10/22/11
Work, Power and Energy Videos
With exams on Monday and Tuesday, here are some videos on the relevant exam topics:
10/21/11
Personal Awareness
One of my favorite shows ever was Star Trek: Deep Space Nine. I love shows that have a darker theme to them, like this show and Babylon 5. B-5 has been available for streaming for a long time now, but DS9 was just put out recently. Ran across this chart today and had to laugh about what it says about me. (Click through for full sized view).
My absolute, hands-down favorite character was Garak (Mr. Chaotic Neutral). My iPhone is named Garak, to give you an idea of my support... And, let's face it - anyone who has met me can easily picture me saying a line like that. My second favorite character was Gul Dukat (Mr. Chaotic Evil). Not sure what this says about me, but today's Friday so who really cares. But it is an interesting exercise when you're reading a book, watching a movie or following a TV series... who are your favorite characters and what is it about them that generates the interest... what part of you resonates with the characters and what does that say about your personality, strengths and weaknesses, abilities and shortcomings...
My absolute, hands-down favorite character was Garak (Mr. Chaotic Neutral). My iPhone is named Garak, to give you an idea of my support... And, let's face it - anyone who has met me can easily picture me saying a line like that. My second favorite character was Gul Dukat (Mr. Chaotic Evil). Not sure what this says about me, but today's Friday so who really cares. But it is an interesting exercise when you're reading a book, watching a movie or following a TV series... who are your favorite characters and what is it about them that generates the interest... what part of you resonates with the characters and what does that say about your personality, strengths and weaknesses, abilities and shortcomings...
Phynally Phryday
A very long week of work (HAH!) ends with an exam review foe C and F Blocks and a tidying up of conservation of energy and power topics for B and E Blocks. Keep very much in mind at power is a rate function and that it ca be approached from a variety of ways involving work and energy. We'll review these ideas on Monday, in preparation for your exam on Tuesday. I'll take some time this weekend to post some video clips about this chapter's topics, so check in occasionally for that help. Have a good weekend!
10/20/11
Ongoing Energy
Today was B Block's chance to run an investigation on conservation of energy. By observing an oscillating spring and making measurements of the kinetic energy and elastic potential energy, it was clear that the total energy was conserved nicely in this system. Attaching an index card to piece of paper to the bottom of the spring made friction a significant force and conservation of mechanical energy was not observed. Concentrate on your conclusion for your write-up tonight - the patterns of the energy conversions, the adherence to conservation of energy, etc. We'll discuss the lab tomorrow and then wrap up ideas with energy conservation and power.
C and F Blocks discussed the idea of power. The word has its own meaning in daily life and that meaning bears no real resemblance to the scientific use - the rate of energy conversion or the rate at which work is performed. Two machines with different power ratings can absolutely do the same work - the lower-power machine just takes longer. We emphasized that the unit - the Watt - that we see on light bulbs and appliances is the same Watt as for our mechanical energy studies and took some time to observe the power of three computers and a television set. For your poor old parents, remember that electrical power reports the rate of energy consumption by your electronics and every Joule of that energy ends up on the electric bill... tomorrow, we'll go over your power homework problems and review for Monday's exam. Then, it's off to momentum!
E Block strolled through conservation of energy, using their lab focused on energy of a ball thrown into the air as an example. The total energy was nicely conserved in that system, although the energy was continually being converted between gravitational potential and kinetic. When the ball was bounced on the floor, however, conservation of mechanical energy faltered. There was significant loss to non-mechanical forms and the overall energy declined with each bounce. We'll go over your conservation of energy problems tomorrow, then move into power.
C and F Blocks discussed the idea of power. The word has its own meaning in daily life and that meaning bears no real resemblance to the scientific use - the rate of energy conversion or the rate at which work is performed. Two machines with different power ratings can absolutely do the same work - the lower-power machine just takes longer. We emphasized that the unit - the Watt - that we see on light bulbs and appliances is the same Watt as for our mechanical energy studies and took some time to observe the power of three computers and a television set. For your poor old parents, remember that electrical power reports the rate of energy consumption by your electronics and every Joule of that energy ends up on the electric bill... tomorrow, we'll go over your power homework problems and review for Monday's exam. Then, it's off to momentum!
E Block strolled through conservation of energy, using their lab focused on energy of a ball thrown into the air as an example. The total energy was nicely conserved in that system, although the energy was continually being converted between gravitational potential and kinetic. When the ball was bounced on the floor, however, conservation of mechanical energy faltered. There was significant loss to non-mechanical forms and the overall energy declined with each bounce. We'll go over your conservation of energy problems tomorrow, then move into power.
10/19/11
Watching the Rise and Fall
C Block worked on a lab that focused on energy transformations and energy conservation for an oscillating spring. The spring constant was experimentally determined and used for the calculation of elastic potential energy. The object's mass was a known value and the motion detector provided displacement and velocity information for the final energy determinations. 
The graphs of kinetic energy and elastic potential energy showed nicely the inverse relationship between the two and adding a plot of total energy demonstrated its conservation throughout the oscillations. No matter how often the energy is transformed, the total remains the same. Adding an index card to the bottom of the oscillating mass increased air resistance and the conservation of mechanical energy suffered due to energy transformation to non-mechanical forms. We'll discuss the lab in class tomorrow, go over the conservation of energy homework problems, then launch into a discussion of power.
B and E Blocks finished up our basic mechanical energy forms by adding gravitational potential and elastic potential to the list. Both are energies of position and both represent stored energy. Both are related to the amount of work done on or by the object and both are readily accessible by objects for work. When working problems, make sure to double-check the reference point for measuring height for gravitational potential energy. It isn't always the ground...
F Block took time to review kinetic and potential energies before looking at conservation of energy. Conservation of total energy is a fundamental law of the universe, but conservation of mechanical energy is valid only in low-friction systems. Transformation of mechanical energy to non-mechanical forms or forms useless for motion will reduce the overall mechanical energy the system has available over time. We are going to assume for your homework problems that mechanical energy is well conserved so that MEi = MEf. It is up to you, though, to use that relationship to come up with a proper equation to work with this concept in specific situations. We'll go over these problems tomorrow and then take a look at power.
The graphs of kinetic energy and elastic potential energy showed nicely the inverse relationship between the two and adding a plot of total energy demonstrated its conservation throughout the oscillations. No matter how often the energy is transformed, the total remains the same. Adding an index card to the bottom of the oscillating mass increased air resistance and the conservation of mechanical energy suffered due to energy transformation to non-mechanical forms. We'll discuss the lab in class tomorrow, go over the conservation of energy homework problems, then launch into a discussion of power.B and E Blocks finished up our basic mechanical energy forms by adding gravitational potential and elastic potential to the list. Both are energies of position and both represent stored energy. Both are related to the amount of work done on or by the object and both are readily accessible by objects for work. When working problems, make sure to double-check the reference point for measuring height for gravitational potential energy. It isn't always the ground...
F Block took time to review kinetic and potential energies before looking at conservation of energy. Conservation of total energy is a fundamental law of the universe, but conservation of mechanical energy is valid only in low-friction systems. Transformation of mechanical energy to non-mechanical forms or forms useless for motion will reduce the overall mechanical energy the system has available over time. We are going to assume for your homework problems that mechanical energy is well conserved so that MEi = MEf. It is up to you, though, to use that relationship to come up with a proper equation to work with this concept in specific situations. We'll go over these problems tomorrow and then take a look at power.
10/18/11
Riding the Energy Train
Our discussion of work and energy continued today with various people starting at various places. B Block and F Blocks took on the topic of potential energy, with the two examples on stage now being gravitational potential and elastic potential. Easily accessed for work, unlike chemical or nuclear, those forms of potential energy get lumped, along with kinetic energy, as mechanical energy. We looked at both of those energies conceptually and mathematically and will review our work tomorrow before moving on to conservation of energy.
Which was where C Block picked up today. Energy does not care what it is at any time - it readily converts and transforms between forms and types. The only caveat is that the total value is always conserved. Mechanical energy, no so much, due to transformations into unusable, non-mechanical forms, but total energy most certainly is conserved quantity. For mechanical energy, as long as friction and other factors are kept at bay, mechanical energy is conserved well enough to make some good predictions about the behavior of objects. Common problems involve solving for a final velocity for an object falling from a height (with or without an initial velocity)and predicting how high something will rise given a launch velocity. Sometimes the problems would be accessible using kinematics formulas, but they fall down when acceleration is not constant and get complicated when the motion covers two or three dimensions getting to its final location. We'll go over your homework problems tomorrow before moving into power.
E Block began their discussion of work and the work-kinetic energy theorem after a discussion of yesterday's lab. Although we highlight the relationship between work and kinetic energy, a similar relationship exists between work and change of potential energy. We'll dig deeper into potential energy tomorrow, highlighting the one you've worked with in lab, gravitational potential energy and adding a new one, elastic potential energy.
Which was where C Block picked up today. Energy does not care what it is at any time - it readily converts and transforms between forms and types. The only caveat is that the total value is always conserved. Mechanical energy, no so much, due to transformations into unusable, non-mechanical forms, but total energy most certainly is conserved quantity. For mechanical energy, as long as friction and other factors are kept at bay, mechanical energy is conserved well enough to make some good predictions about the behavior of objects. Common problems involve solving for a final velocity for an object falling from a height (with or without an initial velocity)and predicting how high something will rise given a launch velocity. Sometimes the problems would be accessible using kinematics formulas, but they fall down when acceleration is not constant and get complicated when the motion covers two or three dimensions getting to its final location. We'll go over your homework problems tomorrow before moving into power.
E Block began their discussion of work and the work-kinetic energy theorem after a discussion of yesterday's lab. Although we highlight the relationship between work and kinetic energy, a similar relationship exists between work and change of potential energy. We'll dig deeper into potential energy tomorrow, highlighting the one you've worked with in lab, gravitational potential energy and adding a new one, elastic potential energy.
10/17/11
Full of Energy
B and F Blocks began their study of work and energy today by nailing down the scientific use of the term "work," looking at how the direction of an applied force affects the amount of work it does on an object, examining situations involving positive and negative work and relating work to the kinetic energy change of a object. For F Block, the lab we conducted yesterday helped to highlight the ideas of work and energy. The ball's fluctuations in kinetic energy related to it's speed and represented the work done on it by the person throwing the ball and by gravity while the ball was in free fall. You did positive work on the ball tossing it upwards (sped up), gravity did negative work on the ball on the rise (slowed down) and positive work on the way down (sped up) and you did negative work on the ball when you caught it (brought it to a stop). Tomorrow, we'll add the potential energy piece to the mix.
C Block built on their study of work and kinetic energy by adding in two potential energies we class as mechanical energies - gravitational potential (PEg) and elastic potential (PEelastic). Both are readily available for active work, unlike chemical or heat, and are easily convertible to kinetic energy. Both are energies of position - position in earth's gravitational field and final position based on stretch or compression. Changes in position (lifting, dropping, stretching, compressing) represent work being done - these energies represent the stored work that you did. Release that energy and that equivalent of work can now be done by the object. On Wednesday, you'll do a lab that will look at potential energy and it's conversion to kinetic in a dynamic system. That lab will also bring in tomorrow's discussion about conservation of energy.
E Block conducted a lab that looked at energy conversions for a ball tossed in the air. You tracked the changes in kinetic and gravitational potential energy and clearly saw the inverse relationship between the two. The total energy, however, remained constant, demonstrating the conservation of mechanical energy in that low-friction system. That went down the tubes when you allowed the ball to bounce on the floor. Mechanical energy was not conserved as a goodly portion of it was converted to heat, internal energy and sound with each bounce. Total energy in a closed system is always conserved, but mechanical energy declines with time due interactions with other objects in the system. We'll go over the lab tomorrow and refer to it frequently in our discussions of work and energy in this chapter.
C Block built on their study of work and kinetic energy by adding in two potential energies we class as mechanical energies - gravitational potential (PEg) and elastic potential (PEelastic). Both are readily available for active work, unlike chemical or heat, and are easily convertible to kinetic energy. Both are energies of position - position in earth's gravitational field and final position based on stretch or compression. Changes in position (lifting, dropping, stretching, compressing) represent work being done - these energies represent the stored work that you did. Release that energy and that equivalent of work can now be done by the object. On Wednesday, you'll do a lab that will look at potential energy and it's conversion to kinetic in a dynamic system. That lab will also bring in tomorrow's discussion about conservation of energy.
E Block conducted a lab that looked at energy conversions for a ball tossed in the air. You tracked the changes in kinetic and gravitational potential energy and clearly saw the inverse relationship between the two. The total energy, however, remained constant, demonstrating the conservation of mechanical energy in that low-friction system. That went down the tubes when you allowed the ball to bounce on the floor. Mechanical energy was not conserved as a goodly portion of it was converted to heat, internal energy and sound with each bounce. Total energy in a closed system is always conserved, but mechanical energy declines with time due interactions with other objects in the system. We'll go over the lab tomorrow and refer to it frequently in our discussions of work and energy in this chapter.
10/14/11
Hello Work and Energy!
B and E Blocks took their forces and laws of motion exam and will get a start on the concepts of work and energy on Monday, with E Block conducting an investigation on conservation of energy. The preliminary questions for the lab that you are working on for homework will introduce you to the relevant ideas for the lab and give you some tools to interpret the results. B Block will engage in a discussion of work and kinetic energy and how they relate through the work-kinetic theorem.
C Block started their work discussion today. The scientific use of the term "work" was highlighted as was the formula we use to calculate work. Remember that the force in the formula is the net force acting on the object and the work assessed will be the next work the object experiences. Positive net force delivers positive work and negative net force delivers negative work. What this can mean is that an object speeds up (+work) or slows down (-work), starts from rest, comes to a stop, or changes direction. But, there must be some displacement for work to be done by that force and, further, the force must have at least some component in the plane of the motion for it to contribute to work. So, for a box sliding across the floor, gravity does no work on the box since the motion is purely horizontal, but weight acts vertically. Because work can produce a change of velocity, it can produce a change in kinetic energy the amount of that change is equal to the work done on or by the object. The work-kinetic energy theorem lets you assess work by measuring velocity changes or use a work value to predict a resulting velocity change for an object. We'll add another energy to our list on Monday, gravitational potential energy and add several more as the year goes on.
F Block conducted an investigation concerning conservation of energy with a ball tossed in the air. You were able to see the patterns of kinetic energy and gravitational potential energy change for the ball in free fall and those changes matched what we would predict based on what we know about free-fall motion. The energy graphs nicely showed that as kinetic energy decreased, gravitational potential increases and vice versa so that the total energy in the system remained constant. For your conclusion section, make sure to include the Extension piece with the bouncing ball (is conservation of energy observed for the bouncing ball - why or why not) and what we would have observed for a high bounce ball in the same situation. On Monday, we will begin our discussion of work and energy and use the lab for that lecture and subsequent ones to illustrate our points.
Have a good weekend!
C Block started their work discussion today. The scientific use of the term "work" was highlighted as was the formula we use to calculate work. Remember that the force in the formula is the net force acting on the object and the work assessed will be the next work the object experiences. Positive net force delivers positive work and negative net force delivers negative work. What this can mean is that an object speeds up (+work) or slows down (-work), starts from rest, comes to a stop, or changes direction. But, there must be some displacement for work to be done by that force and, further, the force must have at least some component in the plane of the motion for it to contribute to work. So, for a box sliding across the floor, gravity does no work on the box since the motion is purely horizontal, but weight acts vertically. Because work can produce a change of velocity, it can produce a change in kinetic energy the amount of that change is equal to the work done on or by the object. The work-kinetic energy theorem lets you assess work by measuring velocity changes or use a work value to predict a resulting velocity change for an object. We'll add another energy to our list on Monday, gravitational potential energy and add several more as the year goes on.
F Block conducted an investigation concerning conservation of energy with a ball tossed in the air. You were able to see the patterns of kinetic energy and gravitational potential energy change for the ball in free fall and those changes matched what we would predict based on what we know about free-fall motion. The energy graphs nicely showed that as kinetic energy decreased, gravitational potential increases and vice versa so that the total energy in the system remained constant. For your conclusion section, make sure to include the Extension piece with the bouncing ball (is conservation of energy observed for the bouncing ball - why or why not) and what we would have observed for a high bounce ball in the same situation. On Monday, we will begin our discussion of work and energy and use the lab for that lecture and subsequent ones to illustrate our points.
Have a good weekend!
10/13/11
One Set of Exams Down
C and F Blocks had their Forces and Laws of Motion exam today. Some folks need some more time and are filing in tomorrow before school to finish up. In class, C Block will begin their investigation of work and energy with discussion of work. F Block will investigate conservation of energy and conversions between kinetic energy and gravitational potential energy. You're homework tonight is to answer those preliminary questions at the start of the lab and that might involve a perusal of Chapter 5 to nail down the answers. But, it will also get you thinking about the lab concepts and provide a foundation to understand your results. And, I expect you to demonstrate that understanding in the Conclusion section of your lab write-up.
B and E Blocks take their exams tomorrow and if you need more help, see me tomorrow before school. You do have all the skills to work the problems, but you have to be able to decide which skills to use and apply them appropriately. And, don't neglect the basic content and concepts. It is easy to focus only on the math and forget basic definitions and ideas that the math supports. On Monday, we'll begin our study of work and energy with E Block conducting an investigation on energy and energy conservation and B Block diving into the topic of work.
B and E Blocks take their exams tomorrow and if you need more help, see me tomorrow before school. You do have all the skills to work the problems, but you have to be able to decide which skills to use and apply them appropriately. And, don't neglect the basic content and concepts. It is easy to focus only on the math and forget basic definitions and ideas that the math supports. On Monday, we'll begin our study of work and energy with E Block conducting an investigation on energy and energy conservation and B Block diving into the topic of work.
10/12/11
Finishing Forces
C and F Blocks spent the period tidying up loose ends with friction and air resistance and reviewing for tomorrow's exam. We walked through the chapter page by page highlighting what to pay attention to and highlighted the math skills you will be required to demonstrate. Although there are only two new formula pieces added this chapter - Fnet = ma and μk,s = Fk,s/FN - using those formulas is not necessarily straight forward and require careful reading of the problem and drawing accurate force diagrams to puzzle out. Also, be on the look out for the need to perhaps use a kinematics formula to work out acceleration for a calculation of net force. Now, I tried to make this obvious in class, but in case you weren't listening, expect a couple of short answers, one of which is going to be an incline problem. Don't be surprised if you are asked to:
So come ready to tackle that and if you need help, see me before school tomorrow.
B and E Blocks finished up with friction and air resistance in class today. B Block reviewed their homework problems for friction and their Chapter 3 exams and E Block finished their discussion of friction and will go over their friction problems tomorrow. Come with questions as we review for Friday's exam and see me before school if you need any additional help.
- Calculate the weight of an object
- Calculate the normal force acting on the object
- Calculate the force pulling it down the incline
- Calculate the force of static friction holding it stationary on the incline
- Calculate the coefficient of friction between the incline and the object
So come ready to tackle that and if you need help, see me before school tomorrow.
B and E Blocks finished up with friction and air resistance in class today. B Block reviewed their homework problems for friction and their Chapter 3 exams and E Block finished their discussion of friction and will go over their friction problems tomorrow. Come with questions as we review for Friday's exam and see me before school if you need any additional help.
10/11/11
Cat's Paw
This is considered the closest thing the original Star Trek has to a Halloween episode... enjoy (even with the stupid commercials)...
Wake Up!
It's school time again, you slackers with your 4-day weekend. Bright-eyed and bushy-tailed we march onwards!
B Block conducted a lab investigation that targeted static and kinetic friction. We measured those values for a block of wood stationary on and moving across your lab table, highlighting the value for Fs,max, the way in which the graphs demonstrated equilibrium and how varying the normal force varied both of these friction measurements. With your data, you will also calculate the coefficient of friction between your surfaces. Remember - mass is not weight, so make sure you are using the object's weight to determine the normal force. Also, when you slid your block across the table and used the motion detector to measure the velocity change, it is important that the data was linear, indicating constant acceleration. Use that acceleration value (the slope of the line you recorded) in Newton's 2nd Law of Motion formula to determine the value of kinetic friction acting on the block. Tomorrow, we'll go over the lab (though it is not due until Thursday) and the homework on friction before adding air resistance to the mix. Test now scheduled for Friday.
C, E and F Blocks had their discussion of friction and air resistance,though F Block has a tiny piece to catch tomorrow. Objects are subject to friction whenever they contact other matter, whether they are moving or not. Static friction has a larger value than kinetic friction because of the adhesive bonds that are able to form when objects are stationary against each other. Once in motion, the surface imperfections are important aspects of the surface construction to worry about We discussed how the normal force relates to the magnitude of the frictional force and how to work in those pesky surface imperfections in to an equation to evaluate friction. The coefficient of friction can be experimentally determined in lab and used to assess the value of frictional resistance an object experiences. Doesn't mean the normal force still isn't a player, though. A small car and a large truck on the same road do not experience the same force of friction, even if they have identical tires. The trucks larger weight produces a larger normal force and, so, is subject to a larger force of friction. Tomorrow, we'll tidy up loose ends for C and F Blocks, review and launch into Thursday's exam. E Block's exam is on Friday, but we have more ground to cover, so the extra day is needed.
B Block conducted a lab investigation that targeted static and kinetic friction. We measured those values for a block of wood stationary on and moving across your lab table, highlighting the value for Fs,max, the way in which the graphs demonstrated equilibrium and how varying the normal force varied both of these friction measurements. With your data, you will also calculate the coefficient of friction between your surfaces. Remember - mass is not weight, so make sure you are using the object's weight to determine the normal force. Also, when you slid your block across the table and used the motion detector to measure the velocity change, it is important that the data was linear, indicating constant acceleration. Use that acceleration value (the slope of the line you recorded) in Newton's 2nd Law of Motion formula to determine the value of kinetic friction acting on the block. Tomorrow, we'll go over the lab (though it is not due until Thursday) and the homework on friction before adding air resistance to the mix. Test now scheduled for Friday.
C, E and F Blocks had their discussion of friction and air resistance,though F Block has a tiny piece to catch tomorrow. Objects are subject to friction whenever they contact other matter, whether they are moving or not. Static friction has a larger value than kinetic friction because of the adhesive bonds that are able to form when objects are stationary against each other. Once in motion, the surface imperfections are important aspects of the surface construction to worry about We discussed how the normal force relates to the magnitude of the frictional force and how to work in those pesky surface imperfections in to an equation to evaluate friction. The coefficient of friction can be experimentally determined in lab and used to assess the value of frictional resistance an object experiences. Doesn't mean the normal force still isn't a player, though. A small car and a large truck on the same road do not experience the same force of friction, even if they have identical tires. The trucks larger weight produces a larger normal force and, so, is subject to a larger force of friction. Tomorrow, we'll tidy up loose ends for C and F Blocks, review and launch into Thursday's exam. E Block's exam is on Friday, but we have more ground to cover, so the extra day is needed.
10/8/11
Do Something Good
There are a lot of great charities out there, I'll be plugging Child's Play here soon, for example, and another solid example is DonateGames. They accept donated videogames and consoles and sell them online, with the proceeds benefiting sick kids. Send them pretty much any game or game system and they'll take it, though they also accept good ol' cash via PayPal. Got old games and things hanging around? Consider shipping them out for a good cause. You can also buy used stuff from their site at a nice discount and add to their coffers. They also encourage people to host their own drives to collect games and gaming equipment - might be a nice way for a couple of you guys to accumulate some community service hours and make a real difference in some kid's life. Gamers get such a bad rap in society... it's good to see people shining a good light on the likes of us.
10/6/11
Rolling into the Long Weekend
At least you guys don't have to come in tomorrow - pity the poor teachers who have to sit through meetings and work on curriculum. Yeah, plotting and planning new ways to make you miserable...
B Block got into a deep discussion about friction, both kinetic and static and the concept of the coefficient of friction. Friction jumps up every time matter contacts matter, but the magnitude depends on several things including the nature of the surfaces and the normal force that acts on the object. Static friction always has a larger value for a given situation than kinetic friction and Tuesday's lab will let you explore that in detail. For your homework problems - they're not hard per se, but they tend to require a number of steps to accomplish. Take your time, sketch things out, watch for applied forces being implemented at an angle and consider how that affects the normal force, frictional resistance and net force acting on the object. We'll go over these on Wednesday before touching on air resistance.
C Block conducted a lab on static and kinetic friction and saw clearly how force applied to an object does not necessarily make an object move. You must exceed the maximum amount of static friction the system can produce before motion can occur. Up until that point the value for applied force is balanced by the static friction, so the object stays in equilibrium. Once Fs,max has been exceeded, the object begins moving, but is still subject to kinetic friction. From your data you will be calculating the frictional force acting on your blocks, the coefficient of friction between the block and reflecting on the nature of forces in motion as you move through the analysis questions and write-up. The lab isn't due until Wednesday, so be prepared on Tuesday to ask me any questions you might have about the lab. We'll go over it in a general way, but you need to tell me if you need specific help with a question or calculation.
E Block took up the ideas of weight and the normal force, which will propel us into a discussion of friction on Tuesday. Remember that the magnitudes of weight and the normal force are only equal if the object is on a flat, horizontal surface. Otherwise, FNis only a component of the object's weight. Also, the normal force is affected by applied forces if they act in or have a component that acts perpendicular to the surface. Keep an eye out for those problems and don't forget to add of subtract that value into your calculations. On Tuesday, we'll take up a discussion of friction and you will need to work with both weight and the normal force to successfully manage situations where we include frictional resistance.
F Block started the period by going over Newton's 3rd Law of Motion. When one object contacts another, two forces are immediately and simultaneously generated, equal in magnitude and opposite in direction to each other. To determine the behavior of the objects after the contact, you have to bring those forces into Newton's 2nd Law of Motion and, with the objects' inertia, calculate the resulting acceleration on each object. We then looked at weight, which is easy to confuse with mass, but is something very different. Mass is an inherent property of matter, but weight varies with location since acceleration due to gravity is location-dependent. Weight is a force, reported in Newtons, so make sure that mass is in kilograms and acceleration is in m/s2 when you calculate an object's weight. On Tuesday, we'll tackle the normal force and might dip toes into the area of friction.
Have a great long weekend!
B Block got into a deep discussion about friction, both kinetic and static and the concept of the coefficient of friction. Friction jumps up every time matter contacts matter, but the magnitude depends on several things including the nature of the surfaces and the normal force that acts on the object. Static friction always has a larger value for a given situation than kinetic friction and Tuesday's lab will let you explore that in detail. For your homework problems - they're not hard per se, but they tend to require a number of steps to accomplish. Take your time, sketch things out, watch for applied forces being implemented at an angle and consider how that affects the normal force, frictional resistance and net force acting on the object. We'll go over these on Wednesday before touching on air resistance.
C Block conducted a lab on static and kinetic friction and saw clearly how force applied to an object does not necessarily make an object move. You must exceed the maximum amount of static friction the system can produce before motion can occur. Up until that point the value for applied force is balanced by the static friction, so the object stays in equilibrium. Once Fs,max has been exceeded, the object begins moving, but is still subject to kinetic friction. From your data you will be calculating the frictional force acting on your blocks, the coefficient of friction between the block and reflecting on the nature of forces in motion as you move through the analysis questions and write-up. The lab isn't due until Wednesday, so be prepared on Tuesday to ask me any questions you might have about the lab. We'll go over it in a general way, but you need to tell me if you need specific help with a question or calculation.
E Block took up the ideas of weight and the normal force, which will propel us into a discussion of friction on Tuesday. Remember that the magnitudes of weight and the normal force are only equal if the object is on a flat, horizontal surface. Otherwise, FNis only a component of the object's weight. Also, the normal force is affected by applied forces if they act in or have a component that acts perpendicular to the surface. Keep an eye out for those problems and don't forget to add of subtract that value into your calculations. On Tuesday, we'll take up a discussion of friction and you will need to work with both weight and the normal force to successfully manage situations where we include frictional resistance.
F Block started the period by going over Newton's 3rd Law of Motion. When one object contacts another, two forces are immediately and simultaneously generated, equal in magnitude and opposite in direction to each other. To determine the behavior of the objects after the contact, you have to bring those forces into Newton's 2nd Law of Motion and, with the objects' inertia, calculate the resulting acceleration on each object. We then looked at weight, which is easy to confuse with mass, but is something very different. Mass is an inherent property of matter, but weight varies with location since acceleration due to gravity is location-dependent. Weight is a force, reported in Newtons, so make sure that mass is in kilograms and acceleration is in m/s2 when you calculate an object's weight. On Tuesday, we'll tackle the normal force and might dip toes into the area of friction.
Have a great long weekend!
10/5/11
RIP Steve Jobs
Love him or hate him, the man was smart, savvy, hard-working and left a massive stamp on our culture... I'm gonna miss the guy...
Gotta Love that Newton
Today was filled with Newton's Laws of Motion, with some weight and normal force thrown in for color.
B and C Blocks reviewed their N-2 and N-3 homework, then moved into a discussion of weight and the normal force. Keep in mind when working problems that mass is not weight - you cannot stick an object's mass into a problem when weight is the necessary property. Also, watch out for problems where the situation does not take place on Earth or is in a location on Earth where they provide a specific value for gravitational acceleration. Then "g" will be whatever the value is for that location and not the familiar 9.81 m/s2. A good calculation of weight is critical when assigning a value for normal force in a problem. A surface responds to the push applied on it by an object, so we need the size of that push to determine the response. For horizontal surfaces, FN = Fg. Easy as pie. On an incline; however, because the normal line to the surface is not parallel to the direction of weight, only a portion of that weight generates a responding normal force: FN = mgcosΘ. The other component of the weight - mgsinΘ - acts to accelerate the object down the ramp and factors in when assessing motion of the object up or down the ramp. Normal force, itself, plays a starring role in determining role in the frictional force an object experiences, so we will take time to make sure we can accurately calculate the normal force acting on an object before we start to tackle friction. The lab you guys will run for this unit will investigate friction in detail, so that should help clarify a lot of the concepts we'll discuss in class.
E and F Blocks had a discussion of Newton's Laws of Motion, with E Block making it through Newton's 3rd Law and F Block making it through Newton's 2nd Law. We'll pick up with weight and the normal force for E Block tomorrow and conquer Newton's 3rd Law of Motion and weight for F Block.
B and C Blocks reviewed their N-2 and N-3 homework, then moved into a discussion of weight and the normal force. Keep in mind when working problems that mass is not weight - you cannot stick an object's mass into a problem when weight is the necessary property. Also, watch out for problems where the situation does not take place on Earth or is in a location on Earth where they provide a specific value for gravitational acceleration. Then "g" will be whatever the value is for that location and not the familiar 9.81 m/s2. A good calculation of weight is critical when assigning a value for normal force in a problem. A surface responds to the push applied on it by an object, so we need the size of that push to determine the response. For horizontal surfaces, FN = Fg. Easy as pie. On an incline; however, because the normal line to the surface is not parallel to the direction of weight, only a portion of that weight generates a responding normal force: FN = mgcosΘ. The other component of the weight - mgsinΘ - acts to accelerate the object down the ramp and factors in when assessing motion of the object up or down the ramp. Normal force, itself, plays a starring role in determining role in the frictional force an object experiences, so we will take time to make sure we can accurately calculate the normal force acting on an object before we start to tackle friction. The lab you guys will run for this unit will investigate friction in detail, so that should help clarify a lot of the concepts we'll discuss in class.
E and F Blocks had a discussion of Newton's Laws of Motion, with E Block making it through Newton's 3rd Law and F Block making it through Newton's 2nd Law. We'll pick up with weight and the normal force for E Block tomorrow and conquer Newton's 3rd Law of Motion and weight for F Block.
10/4/11
A Day of Days
Between the storm that left everyone sodden and full day of forces, I'm ready for a nap...
B and C Blocks took time to discuss Newton's 2nd and 3rd Laws of Motion. Many people think of Newton's 2nd Law of Motion purely as the formula Fnet = ma; however, that's a little shallow. From an equation standpoint, you should really think of it as a = Fnet/m. An object's acceleration is directly proportional to the net applied force and inversely proportional to the object's inertia (measured by the mass). For a single object - increase Fnet and the acceleration increases proportionally. For a given magnitude of force, the larger the mass of the object, the smaller the resultant acceleration. The equation is fine for calculations, but keep the general concept in mind, too. It can make general predictions and comparing objects in similar circumstances simple to do.
Newton's 3rd Law of Motion is one that seems so simple, but people really just don't get it. The phrase "for every action, there is an equal and opposite reaction" is so misused, I have to take a lie down sometimes. Newton-3 only deals with the size and direction of forces that arise when objects contact each other. Period. End of it. Finished. No farther you shall go... If it hit a desk with 20N of force downward, the desk applies a 20N upward force on me. If I want to take things a step further and predict what will happen to the motion of the desk and/or my hand after the contact, I have to haul out Newton-2. I know the magnitudes and directions of the forces, now, I have to work with each object's mass to determine their acceleration. Newton-3 does not, in any way, speak to the responses of the objects to the forces. Also, remember that the forces are simultaneously applied - there is no lag time, even though the term "action-reaction forces" is frequently used. Hopefully, today's demonstrations helped solidify a little of this in your minds and you bring the ideas with you to class tomorrow, when we take up looking at specific forces - weight and friction.
E Block conducted their Atwood's Machine lab and, for the conclusion section of your write-up, make sure to consider our discussion yesterday of forces, equilibrium, inertia and Newton's 1st Law of Motion. The wise student might peek ahead to Newton-2 and Newton-3 for additional information to include in your synopsis.
F Block discussed their Atwood's Machine lab and used that to highlight ideas about forces. The concepts of net force, equilibrium, inertia and Newton's 1st Law of Motion were nicely demonstrated by your lab, as was the bones of Newton's 2nd Law of Motion, which we'll discuss in class tomorrow. For the homework tonight, pull out those vector operations skills... you're gonna need them...
B and C Blocks took time to discuss Newton's 2nd and 3rd Laws of Motion. Many people think of Newton's 2nd Law of Motion purely as the formula Fnet = ma; however, that's a little shallow. From an equation standpoint, you should really think of it as a = Fnet/m. An object's acceleration is directly proportional to the net applied force and inversely proportional to the object's inertia (measured by the mass). For a single object - increase Fnet and the acceleration increases proportionally. For a given magnitude of force, the larger the mass of the object, the smaller the resultant acceleration. The equation is fine for calculations, but keep the general concept in mind, too. It can make general predictions and comparing objects in similar circumstances simple to do.
Newton's 3rd Law of Motion is one that seems so simple, but people really just don't get it. The phrase "for every action, there is an equal and opposite reaction" is so misused, I have to take a lie down sometimes. Newton-3 only deals with the size and direction of forces that arise when objects contact each other. Period. End of it. Finished. No farther you shall go... If it hit a desk with 20N of force downward, the desk applies a 20N upward force on me. If I want to take things a step further and predict what will happen to the motion of the desk and/or my hand after the contact, I have to haul out Newton-2. I know the magnitudes and directions of the forces, now, I have to work with each object's mass to determine their acceleration. Newton-3 does not, in any way, speak to the responses of the objects to the forces. Also, remember that the forces are simultaneously applied - there is no lag time, even though the term "action-reaction forces" is frequently used. Hopefully, today's demonstrations helped solidify a little of this in your minds and you bring the ideas with you to class tomorrow, when we take up looking at specific forces - weight and friction.
E Block conducted their Atwood's Machine lab and, for the conclusion section of your write-up, make sure to consider our discussion yesterday of forces, equilibrium, inertia and Newton's 1st Law of Motion. The wise student might peek ahead to Newton-2 and Newton-3 for additional information to include in your synopsis.
F Block discussed their Atwood's Machine lab and used that to highlight ideas about forces. The concepts of net force, equilibrium, inertia and Newton's 1st Law of Motion were nicely demonstrated by your lab, as was the bones of Newton's 2nd Law of Motion, which we'll discuss in class tomorrow. For the homework tonight, pull out those vector operations skills... you're gonna need them...
10/3/11
Dynamics
We launched into our study of dynamics today with a basic overview of forces and a toe-dip into Newton's Laws of Motion. B, C and E Blocks had a discussion focusing on the nature of forces, the difference between field and contact forces and the concepts of net force and equilibrium. We then took the ideas of net force and equilibrium into Newton-land and used them to set up Newton's first law of motion and a discussion of inertia. Objects resist being accelerated and the greater the mass the greater the resistance. Without a net external force, objects are in equilibrium and have a constant velocity (0 m/s if at rest). With a net external force, we will see acceleration of the object and the size of the force, along with the object's inertia determine the magnitude of the acceleration - pretty much that all sums up the take-away lesson for today. Tomorrow, we'll take on Newton's second law and, with our work today on calculating net force, put some numbers to that acceleration value.
F Block worked on a lab investigating Atwood's Machine. Mass difference and total mass were examined on how they affected acceleration of the system. With an increasing mass difference between the two objects, acceleration increased. With the same mass difference, but increasing the system's total mass with each trial, we saw a decreasing acceleration. We'll put vocabulary and concepts to these ideas in class tomorrow, but you should have a good idea now about how force and inertia affect the motion of objects...
F Block worked on a lab investigating Atwood's Machine. Mass difference and total mass were examined on how they affected acceleration of the system. With an increasing mass difference between the two objects, acceleration increased. With the same mass difference, but increasing the system's total mass with each trial, we saw a decreasing acceleration. We'll put vocabulary and concepts to these ideas in class tomorrow, but you should have a good idea now about how force and inertia affect the motion of objects...
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