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...
9/30/11
Test Day!
Everyone had their Chapter 3 test today and, I'll be honest, I wasn't surprised to see people taking a long time to finish. This exam always gives people more trouble than any other. Some suggestions I can make:
Monday begins our study of forces. F Block will conduct a lab investigation on forces and equilibrium and the rest of you lot will dive into the nature of forces, free-body diagrams and may get a taste of Newton's first law of motion. Have a good weekend!
- When I say something will definitely be on the test - it will. I said there would be a projectile-launched-at-an-angle question on the exam and even what I'd ask for it. People should have practiced that one so it went smooth as silk.
- Listen closely in class when I outline what information will be available to you. For instance, if you got slowed down by the formulas I provided, remember that I told you exactly what you would get. Let that guide your studying, not other resources will not be available if you don't remember them exactly.
- For all exams - look for patterns. Often a problem that seems new and unique, isn't. It's another problem you did just from a different point of view. The airplane dropping a box problem is basically your ball rolling off the table problems, kicking a rock off a cliff problem, etc. They work the same way and the same assumptions/implicit knowledge applies.
- Since we go over homework before you turn it in, use that help as a check for when you need extra help. Waiting until the last minute can leave you with too many questions and not enough time to process any answers. Also, I cannot always be available at a moment's notice to stay after school. Count on asking me one day to stay the next or to see you the following morning. If I can stay that afternoon, I'll let you know, but if you budget your time wisely, you can get the help you need and not be frustrated because I have to take the dogs to the vet and can't stay after school when you want/need me
Monday begins our study of forces. F Block will conduct a lab investigation on forces and equilibrium and the rest of you lot will dive into the nature of forces, free-body diagrams and may get a taste of Newton's first law of motion. Have a good weekend!
9/29/11
Geek Test
+10 geek points if you've seen at least one episode with each of these... ok, one only had one episode, so you have to be a real geek to have seen it...
Test Day -1
Tomorrow, everyone has their Chapter 3 test. Today, we reviewed through the material, page by page, highlighting what you should know and be able to do for tomorrow. Hopefully, you downloaded the review sheet that's been up on Edline and have been studying a little at a time for the exam. Putting it all off until the last minute is not a great idea, especially if what you have trouble with is the problem-solving piece. You can't last-minute-memorize the skills needed for that part of the exam, so I am hopeful that everyone who has needed extra help has seen me to get the assistance they needed. On Monday, we begin our look at forces, the culprit promoting acceleration.
9/28/11
Winding Down with Kinematics
Today, groups either cleaned up notions about projectiles or jumped into relative motion. Unfortunately, a meeting pulled me out of class for C and E blocks, but we'll have plenty of time to pick up relative velocity tomorrow as we review for Friday's exam. B Block conducted their Projectile Motion lab and got to put into practice the concepts and calculations we discussed in class. As we look towards Friday, here are some videos to help you with working problems dealing with projectiles:
9/27/11
And More Projectiles...
Although B Block did start their discussion of relative motion today, the first portion of their period and the other blocks of the day continued on with projectiles. C Block conducted their Projectile Motion lab, investigating the properties of and practicing calculations with horizontally-launched projectiles. E and F Blocks had more practice time working with projectiles launched at angle, which we will go over tomorrow. Remember - the exam is on Friday, so Thursday is going to be some review time for people. I'd start looking over things now and be ready with questions...
9/26/11
Projectiles!
Today was projectiles launched at an angle day for all blocks - some getting their first bite at the information, others getting some review and more practice. Horizontally-launched projectile are a little easier to work with since we have only 1/2 of a parabola to work with and we know that vi,y will be 0 m/s. That goes out the window for many projectiles, such as balls thrown through the air or missiles launched at a target. Some of the initial velocity is in the x-direction and some is in the y-direction, and you need to find those values and use them appropriately in your analyses. Most often, the x-component of the initial velocity will be found through the cosine function and the y-component through the sine function. So, for a problem where a projectile was launched at 20 m/s at an angle of 30°, you would see me write on the board:
vx = 20 m/s(cos 30°)
vi,y = 20 m/s(sin 30°)
right off the bat. Then, just make sure to use the proper velocity component when you work in the x- or y-directions. Another helpful trick is to break the parabola in two. This can make solving for time in the air simple. Solve for time for one-half of the parabola and then multiply times two to get full time in the air. Then, with that time, finding horizontal range is super simple (vx = Δx/t). Different groups have different problems that they are working on tonight, and we will check over them tomorrow before moving forward. If more practice is needed, we'll take the time to do that. C Block will be doing a lab on horizontally-launched projectiles and some groups may dip toes in relative motion, depending on quickly we move through our projectiles review. Test on Friday and the Chapter 3 review sheet is up on Edline. Then - Forces!
vx = 20 m/s(cos 30°)
vi,y = 20 m/s(sin 30°)
right off the bat. Then, just make sure to use the proper velocity component when you work in the x- or y-directions. Another helpful trick is to break the parabola in two. This can make solving for time in the air simple. Solve for time for one-half of the parabola and then multiply times two to get full time in the air. Then, with that time, finding horizontal range is super simple (vx = Δx/t). Different groups have different problems that they are working on tonight, and we will check over them tomorrow before moving forward. If more practice is needed, we'll take the time to do that. C Block will be doing a lab on horizontally-launched projectiles and some groups may dip toes in relative motion, depending on quickly we move through our projectiles review. Test on Friday and the Chapter 3 review sheet is up on Edline. Then - Forces!
9/24/11
9/23/11
Projectile Motion
All blocks today worked with projectile motion - some blocks working with horizontal projectiles and others with projectiles launched at angle. B and C blocks worked with projectiles launched at an angle, building on the techniques they practiced with horizontally-launched projectiles. We lose the ability to set the initial velocity in the y-direction to 0 m/s, which complicates matters, but if you work thoughtfully and in a stepwise fashion, the problems are manageable. Break the initial velocity into it's x-and y-components, remember that vx is constant and the y-velocity at the top of the rise is 0 m/s and that if you launch and land at the same point, you have a symmetrical parabola. That last piece can be of great help, since sometimes it is easy to work with one half of the parabola, rather than the whole thing, and just multiply your values by two. Solve for time to top of rise and multiply by two to get the entire time in the air, for instance. On Monday, we will look over these some more and get more practice, if necessary.
E Block worked on the Projectile Motion lab, which verified the assumptions and calculations we worked on with our practice problems. As long as you know height, you can calculate how long it takes the projectile to hit the ground. With time and and a known, constant horizontal velocity, predicting horizontal displacement is quick and easy. We'll go over this lab on Monday and then start on projectiles launched at an angle.
F Block had their horizontal projectile lecture, which helped to clarify and explain observations made in yesterday's lab. Yes, the velocity in the x-direction is constant. Yes, the acceleration in the y-direction is the standard velocity for gravity. Yes, you can analyze each component of the motion separately, for they are independent. Use the skills you practice in lab and the example problem we worked on the board to tackle the homework problems this weekend. On Monday, we'll go over them and then start with projectiles launched at an angle.
Have a good weekend!
E Block worked on the Projectile Motion lab, which verified the assumptions and calculations we worked on with our practice problems. As long as you know height, you can calculate how long it takes the projectile to hit the ground. With time and and a known, constant horizontal velocity, predicting horizontal displacement is quick and easy. We'll go over this lab on Monday and then start on projectiles launched at an angle.
F Block had their horizontal projectile lecture, which helped to clarify and explain observations made in yesterday's lab. Yes, the velocity in the x-direction is constant. Yes, the acceleration in the y-direction is the standard velocity for gravity. Yes, you can analyze each component of the motion separately, for they are independent. Use the skills you practice in lab and the example problem we worked on the board to tackle the homework problems this weekend. On Monday, we'll go over them and then start with projectiles launched at an angle.
Have a good weekend!
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