9/22/11
Bombing the Enemy
F Block conducted a lab investigation on horizontally-launched projectiles. The mission was simple - use photogates to determine the velocity of a ball-bearing, take the height of the launch platform and determine where to place the target for the bearing to hit. The thing was, the bearing was only allowed to hit the ground once - when groups were ready to make their bombing run for me (and the rest of the class to see). This lab required careful measurements of horizontal velocity and height and careful calculation of the bearing's horizontal displacement. Groups did an excellent job - the targets were either nailed on the first go or with a little lateral adjustment of the target. The range calculations were fine, but the launch ramp and target were a little off right-left. Tomorrow, E Block sees if they can make as good a showing...
B and C Blocks reviewed the idea of projectiles launched horizontally and had class time to work practice problems for this type of motion. Remember that time is y-dependent and the most commonly used formula to find time for these problems is Δy = vot + 1/2at2. Since the initial velocity in the y-direction is 0 m/s, the formula simplifies to: Δy = 1/2at2. Once you have time, solving for horizontal aspects of the motion is simple. You've got one formula to use: vx = Δx/t. You're generally asked for either horizontal displacement (and they give you vx) or for launch velocity (and they give you Δx). Just use the time you found for the y-component of the motion and you're good as gold. We'll look over these tomorrow and then start to discuss projectiles launched at an angle. They take a bit more work, but it builds on what we've already done, so it won't be exhausting.
E Block had their full horizontally-launched projectiles chat today and also has a set of problems to work. We'll be going over those on Monday, since tomorrow is your lab block. I'd get them out of the way tonight for two reasons:
For everyone, the test is looking like it will be next Friday. That's a little later than I had planned but we're losing a couple of periods next week for various things, so c'est la vie...
B and C Blocks reviewed the idea of projectiles launched horizontally and had class time to work practice problems for this type of motion. Remember that time is y-dependent and the most commonly used formula to find time for these problems is Δy = vot + 1/2at2. Since the initial velocity in the y-direction is 0 m/s, the formula simplifies to: Δy = 1/2at2. Once you have time, solving for horizontal aspects of the motion is simple. You've got one formula to use: vx = Δx/t. You're generally asked for either horizontal displacement (and they give you vx) or for launch velocity (and they give you Δx). Just use the time you found for the y-component of the motion and you're good as gold. We'll look over these tomorrow and then start to discuss projectiles launched at an angle. They take a bit more work, but it builds on what we've already done, so it won't be exhausting.
E Block had their full horizontally-launched projectiles chat today and also has a set of problems to work. We'll be going over those on Monday, since tomorrow is your lab block. I'd get them out of the way tonight for two reasons:
- They will help you with you lab calculations tomorrow.
- You'll have the lab write-up to do over the weekend, so don't give yourself double homework.
For everyone, the test is looking like it will be next Friday. That's a little later than I had planned but we're losing a couple of periods next week for various things, so c'est la vie...
9/21/11
Horizontal Projectiles
Here's a decent video discussing the basics of projectile motion, using a horizontally-launched projectile as an example:
Straddling a Line
Two blocks today dove into projectile motion and two blocks delved deeper into vector operations and non-perpendicular vectors. B and C Blocks began their discussion of projectile motion and we started with basic characteristics of this type of motion and spent time focusing on projectiles launched horizontally. Projectiles can be thought of objects in free fall that are given a little bonus - a horizontal velocity. Remember that whatever happens in the horizontal direction is independent of the party going on in the vertical plane and vice versa. So, the components of the motion can be analyzed independently using our familiar kinematics formulas. For motion in the x-direction, the velocity (in the absence of air resistance) remains constant, because there is no net external force acting in that direction to accelerate the object. Motion in the y-direction is accelerated by gravity. Everything we talked about and practiced for an object being dropped or tossed straight up into the air applies to the vertical motion of a projectile. Also, remember that the initial velocity in the vertical direction for a horizontal projectile is 0 m/s. Tomorrow, we'll finish up that chat and work problems with this type of projectile before adding another twist - what do you do with a projectile launched at an angle?
E and F Blocks reviewed vector resolution and working with non-perpendicular vectors. The most attention was given to those non-perpendicular beasts, because they are a handful to work with. Read the problem closely and carefully draw your vector diagram. Don't be afraid to draw the first vector, then draw a nice coordinate plane at the tip of this guy. Then, draw the second right at the tip of the first vector, right at the origin of the grid exactly as if the first vector wasn't there at all. Do that for every vector in the problem. Break down each vector into it's x- and y-components and pay attention to what trig function is used to determine each. Then, make you list of Σx and Σy, making sure the signs of each vector you add to the lists have the proper sign. Now, it's a matter of adding everybody up and making that final, blessed right triangle and getting the magnitude and direction of the resultant. Tomorrow, E Block will start discussing projectile motion and F Block will conduct a lab investigation focusing on horizontally-launched projectiles.
E and F Blocks reviewed vector resolution and working with non-perpendicular vectors. The most attention was given to those non-perpendicular beasts, because they are a handful to work with. Read the problem closely and carefully draw your vector diagram. Don't be afraid to draw the first vector, then draw a nice coordinate plane at the tip of this guy. Then, draw the second right at the tip of the first vector, right at the origin of the grid exactly as if the first vector wasn't there at all. Do that for every vector in the problem. Break down each vector into it's x- and y-components and pay attention to what trig function is used to determine each. Then, make you list of Σx and Σy, making sure the signs of each vector you add to the lists have the proper sign. Now, it's a matter of adding everybody up and making that final, blessed right triangle and getting the magnitude and direction of the resultant. Tomorrow, E Block will start discussing projectile motion and F Block will conduct a lab investigation focusing on horizontally-launched projectiles.
9/20/11
More Vectors!
Today, various discussions were launched for vector resolution and working with non-perpendicular vectors. Both vector combination and vector resolution are going to be used this year as we work with things like force and momentum, so make sure that you are very confident in your vector operation skills. Non-perpendicular vectors are the test - if you can successfully work problems with non-perpendicular vectors, then you can wear the vector crown with pride...
Tomorrow, we'll review these ideas and apply them to the concept of horizontally-launched projectiles. When motion occurs in two dimensions, as it does with projectiles, we have to be able to break a launch velocity into it's horizontal and vertical components to analyze the motion. The lab we'll do for this section will let folks work with horizontally-launched projectiles and give groups a chance to mathematically predict where a ball will fall. Yes... there will be prizes involved...
Tomorrow, we'll review these ideas and apply them to the concept of horizontally-launched projectiles. When motion occurs in two dimensions, as it does with projectiles, we have to be able to break a launch velocity into it's horizontal and vertical components to analyze the motion. The lab we'll do for this section will let folks work with horizontally-launched projectiles and give groups a chance to mathematically predict where a ball will fall. Yes... there will be prizes involved...
9/19/11
Go Go Gamers Go
I have never hidden that I'm a gamer from way back (yeah, had the original Pong that I played on a rickety black and white TV I inherited from my grandparents) and although multiplayer jerks can give gamers a bad name, sometimes we get a bit of good press:
Gamers solve problem in 3 weeks scientists couldn't in 10 years
Gamers solve problem in 3 weeks scientists couldn't in 10 years
Stop that Celebrating
I'll be in tomorrow. Just fighting off a cold and since I hate losing a fight, this cold will be tapping the mat in no time. Everyone is working on vectors today, so I hope that folks are helping each other out. C, E and F Blocks are working vector resolution problems, sort of the flip flop of the vector combination work you did on Friday. Using the same trig relationships, take a look at your vector diagram, decide which side of your triangle is the opposite to the angle and which is the adjacent. Write out your relationship and plug in the information you know. For vector resolution, that part is easy. It's probably going to boil down to either sin Θ • hypotenuse = opposite side or cos Θ • hypotenuse = adjacent side. Now, don't always think that the adjacent side will be the x-axis and the opposite will be the y-axis. Look closely at your diagram to determine the proper relationship to use for each component of your triangle.
B Block got a heavy dose of vector work - don't be upset if you have some problems with the non-perpendicular vector piece. They take very careful attention to diagram-drawing and organization of information. Take each individual vector and resolve it into it's components, paying close attention to the signs of each component. Add up all the x-components of the vectors and all the y-components and use them to make a single right triangle, the hypotenuses of which is the resultant for the overall problem. Think of it as a puzzle or game and don't let yourself get frustrated if you''re having trouble. Put the problems aside, take a few minutes break and come back with a fresh head. We'll start going over this tomorrow and more practice is needed, that's ok.
Well, off to open a fresh box of tissues...
B Block got a heavy dose of vector work - don't be upset if you have some problems with the non-perpendicular vector piece. They take very careful attention to diagram-drawing and organization of information. Take each individual vector and resolve it into it's components, paying close attention to the signs of each component. Add up all the x-components of the vectors and all the y-components and use them to make a single right triangle, the hypotenuses of which is the resultant for the overall problem. Think of it as a puzzle or game and don't let yourself get frustrated if you''re having trouble. Put the problems aside, take a few minutes break and come back with a fresh head. We'll start going over this tomorrow and more practice is needed, that's ok.
Well, off to open a fresh box of tissues...
9/16/11
Vectors
Before we move into 2-dimensional motion, we have to tackle the wonderful world of vectors. The ability to combine and resolve vectors will be critical in this course and we have to make sure that the necessary skills are hammered out now. B, E and F Blocks discussed the properties of vectors today and a method for constructing vector diagrams. We'll use the tail-to-tip method in this class, but if you already know the parallelogram method, go ahead and use it. But, definitely take the time to draw a vector diagram before tackling a problem; you will be surprised how much easier setting up your problem will be and how much better you can visualize the situation with a good diagram staring you in the face. We also took time to demonstrate using the Pythagorean theorem and the tangent function to calculate the magnitude and direction of a resultant vector and will add on the sine and cosine functions when we discuss vector resolution on Monday.
C Block had an overview of vector operations and then worked through a computer simulation that allowed them to work with vectors both graphically and mathematically. You got to combine vectors, resolve vectors and work with situations were there were many vectors involved in a problem. As long as you can get them sorted into vectors along the x-axis and vectors along the y-axis, you can make a nice right triangle to find your resultant. We'll go over that activity on Monday and then put a little more flesh on the vector bone.
Blocks B, E and F may want to practice with the simulation that C Block worked on today, so here it is for your enjoyment (along with the LAB SHEET)
C Block had an overview of vector operations and then worked through a computer simulation that allowed them to work with vectors both graphically and mathematically. You got to combine vectors, resolve vectors and work with situations were there were many vectors involved in a problem. As long as you can get them sorted into vectors along the x-axis and vectors along the y-axis, you can make a nice right triangle to find your resultant. We'll go over that activity on Monday and then put a little more flesh on the vector bone.
Blocks B, E and F may want to practice with the simulation that C Block worked on today, so here it is for your enjoyment (along with the LAB SHEET)
9/15/11
Test Day!
Test day is over!
Well, you've gotten a look at what a typical test looks like and it's not really going to change. Same format each time, so no surprises. If you find you run short of time, it's ok to come back and finish, but always make sure to do it in a very timely fashion. Same goes if you're absent and miss a test. Make it up quickly, since I can't return and discuss the other folks' exams until yours is taken.
Tomorrow, we start with vectors. Some of you have worked with them, others of you haven't. Some of you have worked with basic trig functions (sine, cosine, tangent), others haven't. Not a problem. We'll get everyone up to speed with some good hard grunt work and there will be no complaining! We'll need these skills to be sharp and shiny as we move into 2-dimensional motion and then into our study of every other vector topic we hit this year. C Block has long block tomorrow and we'll start with some basic discussion of vectors, then you will work with a computer simulation to walk you through adding vectors. The rest of you guys will get a more in-depth discussion of vectors and how we can use vectors to explore aspects of physics. Trust me, it won't be too painful...
9/14/11
Commencing Countdown Engines On
Tomorrow is test day for all blocks. We reviewed for all blocks between yesterday and today, literally going page by page through the book to point out relevant things to know. You have all of your homework and labs in your hands. A review sheet is online, as are the worked out solutions to the problems and the PowerPoint lecture. So, you have a mess of tools and experiences to help you tomorrow. Remember that you'll get the formulas and remember to study your Ball Toss lab for the short answer that's going to concentrate on that investigation. I will be in before school tomorrow if you have any final questions, so stop in if you need help. Good Luck!
9/13/11
And More Free Fall
B and C Blocks conducted the Picket Fence Free Fall lab and got nice results. Demonstrated that acceleration due to gravity is constant, graphs of position-time, velocity-time and acceleration-time showed predicted patterns and that the measured value for "g" was pretty durn close to the actual value.
E Block reviewed their lab and homework problems for free fall before launching into a review for Thursday's exam. That's how things usually work - I'll go through the text pointing out what to know, and what you can slack off on, but it's on your shoulders to get any additional help you need before test time. That goes for all the blocks - are you listening B, C and E? Tomorrow, you'll get to work on a lab that will let you more fully work with free fall motion and give you a lot of practice interpreting and doing quantitative analysis of graphs. That will also serve as a good review for the test - remember, the write-up won't be due until Friday.
F Block ran a lab that analyzed the motion of a ball in free fall and spent a good portion of the lab block interpreting the graphs of the ball's motion. Make sure you are very clear about what each graph says about the motion and what information you can get from each graph. Consider well how the ball's motion and the patterns of the graphs document what we talked about in class.
Exam review tomorrow for B, C and E Blocks, so come with questions. Remember the online resources available to you and make good use of them for test preparation. This will not bail you out of a jam:
E Block reviewed their lab and homework problems for free fall before launching into a review for Thursday's exam. That's how things usually work - I'll go through the text pointing out what to know, and what you can slack off on, but it's on your shoulders to get any additional help you need before test time. That goes for all the blocks - are you listening B, C and E? Tomorrow, you'll get to work on a lab that will let you more fully work with free fall motion and give you a lot of practice interpreting and doing quantitative analysis of graphs. That will also serve as a good review for the test - remember, the write-up won't be due until Friday.
F Block ran a lab that analyzed the motion of a ball in free fall and spent a good portion of the lab block interpreting the graphs of the ball's motion. Make sure you are very clear about what each graph says about the motion and what information you can get from each graph. Consider well how the ball's motion and the patterns of the graphs document what we talked about in class.
Exam review tomorrow for B, C and E Blocks, so come with questions. Remember the online resources available to you and make good use of them for test preparation. This will not bail you out of a jam:
9/12/11
Free Fall
Today was dominated by a study of free fall with B, C and F Blocks engaging in a discussion of free-fall motion and E Block working on an activity to experimentally determine the value for acceleration due to gravity. That lab shows quite nicely that can be measured quite simply (as long as you have a photogate) and you'll use another method on Wednesday when you conduct a more extensive investigation on the free fall motion of a ball tossed in the air.
B, C and F Blocks tramped over familiar ground in their study of free fall, since the basic rules and formulas of kinematics apply equally to vertical and horizontal motion. As long as the only force producing significant acceleration on an object is gravity, the motion is easy to describe and predict. You know the acceleration will be -9.81 m/s2 and you know that at the highest point of the rise the velocity of the object will be 0 m/s. If the object is dropped from a height (already at it's highest point), the initial velocity is 0 m/s. Remember this when making your information list to solve problems. The book won't remind you in the problem's write-up, so you'll have to remember that on your own. You know that an object on the rise (with + velocity and - acceleration) will slow down and falling object (with - velocity and - acceleration) will speed up. Tomorrow, B and C Blocks will conduct an activity on acceleration due gravity and F Block will analyze the motion of a ball tossed into the air to determine if all this blah, blah, blah about free fall is really to be believed.
B, C and F Blocks tramped over familiar ground in their study of free fall, since the basic rules and formulas of kinematics apply equally to vertical and horizontal motion. As long as the only force producing significant acceleration on an object is gravity, the motion is easy to describe and predict. You know the acceleration will be -9.81 m/s2 and you know that at the highest point of the rise the velocity of the object will be 0 m/s. If the object is dropped from a height (already at it's highest point), the initial velocity is 0 m/s. Remember this when making your information list to solve problems. The book won't remind you in the problem's write-up, so you'll have to remember that on your own. You know that an object on the rise (with + velocity and - acceleration) will slow down and falling object (with - velocity and - acceleration) will speed up. Tomorrow, B and C Blocks will conduct an activity on acceleration due gravity and F Block will analyze the motion of a ball tossed into the air to determine if all this blah, blah, blah about free fall is really to be believed.
9/9/11
West Nile Virus
As you all know, we got the word that there mosquitoes in the area that tested positive for West Nile Virus. For more information:
Here's the cycle of infection:
Here's the culprit:
And here's the ad for the upcoming Universal Pictures film starring Keanu Reeves:
...ok... that last part was a lie...
Here's the cycle of infection:
Here's the culprit:
And here's the ad for the upcoming Universal Pictures film starring Keanu Reeves:
...ok... that last part was a lie...
Phinally Phriday!
And, phinally, the sun has peeked out. I will take this as a good omen...
Today was kinematics for B, C and F Blocks, which nicely capped off our stepwise investigation of the descriptors of motion (displacement, velocity, acceleration). Kinematics asks and answers questions about an object's motion, but what it does not address is the cause of the motion or the factors promoting a change in the motion. That's dynamics, and we'll catch that very soon. The homework problems are designed to give you practice in working with these formulas and, I strongly urge folk to really give them a try before looking up answers. Write down all your information and identify which variable each piece represents. Choose a formula to start working with that uses that information, or could be used to get you another piece of information with what you already have provided. Plug your variables into the formula and be very mindful of signs. Evaluate your answer logically and with common sense - does it seem right or not... Create a good problem-solving strategy now, because we are going to be doing this until June...
E Block discussed their Ball Toss lab and evaluated their results in light of our previous work on kinematics. The tossed ball is an example of an object in free-fall (if we assume friction is negligible, which our results said wasn't a bad assumption) and that was the topic of today's lecture. Free-fall motion is motion where the only force acting on the object is gravity. Anything tossed into the air or dropped from a height, without any additional propulsion supplied, is a candidate for free-fall. We spent time explaining the patterns of motion associated with free fall (lose velocity as rises, gains velocity as falls) in terms of our knowledge of the interplay between acceleration and velocity and added a few items to our mental tool box (acceleration due to gravity is constant and at the top of a rise and object's velocity is 0 m/s) to help set up and solve problems. On Monday, you will do an activity to demonstrate free-fall motion and establish experimentally a value for acceleration due to gravity.
Have a great weekend!
Today was kinematics for B, C and F Blocks, which nicely capped off our stepwise investigation of the descriptors of motion (displacement, velocity, acceleration). Kinematics asks and answers questions about an object's motion, but what it does not address is the cause of the motion or the factors promoting a change in the motion. That's dynamics, and we'll catch that very soon. The homework problems are designed to give you practice in working with these formulas and, I strongly urge folk to really give them a try before looking up answers. Write down all your information and identify which variable each piece represents. Choose a formula to start working with that uses that information, or could be used to get you another piece of information with what you already have provided. Plug your variables into the formula and be very mindful of signs. Evaluate your answer logically and with common sense - does it seem right or not... Create a good problem-solving strategy now, because we are going to be doing this until June...
E Block discussed their Ball Toss lab and evaluated their results in light of our previous work on kinematics. The tossed ball is an example of an object in free-fall (if we assume friction is negligible, which our results said wasn't a bad assumption) and that was the topic of today's lecture. Free-fall motion is motion where the only force acting on the object is gravity. Anything tossed into the air or dropped from a height, without any additional propulsion supplied, is a candidate for free-fall. We spent time explaining the patterns of motion associated with free fall (lose velocity as rises, gains velocity as falls) in terms of our knowledge of the interplay between acceleration and velocity and added a few items to our mental tool box (acceleration due to gravity is constant and at the top of a rise and object's velocity is 0 m/s) to help set up and solve problems. On Monday, you will do an activity to demonstrate free-fall motion and establish experimentally a value for acceleration due to gravity.
Have a great weekend!
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