Jimpulse and Rhomentum
This week we did an independent unit on Impulse and Momentum (I like to call them Jimpulse, cause Impulse's symbol is a J, and Rhomentum, because Momentum's symbol is a Rho which looks like a p). In other physics classes, we were told that impulse equals momentum, but in Mr. Fullerton's Physics AP-C class we did a lab and a few worksheets that proved just that!
In a lab we did this week we used a force and velocity sensor, and pushed a cart on a track connected by rubber band to the force sensor. Using logger pro, we obtained the force vs. time graph and position vs time graph. When we took the area of the force vs. time graph (the definite integral) it was the same number as the slope (the derivative) of the position vs time graph multiplied by the mass of the cart. And there you have it. The integral of Force with respect to time is Impulse (since ) and mass times velocity is Momentum (Since , and the initial velocity was zero). Since those two numbers were the same no matter how hard we pushed the cart, we proved that or !
When you get a fairly well understanding of Impulse and Momentum, you start to look at everyday things you might see differently, and some things might make sense all of the sudden. For example - skateboarding .
The "Ollie" is the fundamental trick of skateboarding. It takes years for some to master, but it is essential if you want to skateboard. An ollie is a trick that allows the skateboarder to jump with the skateboard. His feet are not attached to the skateboard, so it would seem difficult to jump and have the board follow behind! But, there is a way, shown here:
The ollie! The secret about it is not to jump first. Before jumping you need to stomp down on the tail of the board, causing it to hit the ground. The more force you put on the tail of the board, the higher you will potentially be able to ollie. When the tail of the board strikes the ground, you get an impulse. The board comes in contact with the ground for a certain time, and when you increase the force, you increase the impulse. Since every action has an equal and opposite reaction, (New told me so!!), the impulse from the board to the ground equals the impulse from the ground to the board. Impluse = Momentum, so . Since the ground has a lot of mass, the velocity is very slow (arbitrarily close to 0 ) but the skateboard and boarder have a smaller mass, so the velocity is enough to propell the boarder upwards!
At that exact moment that impulse acts, the skateboarder jumps and the skateboard follows. The skateboarder guides the side of his foot up the grip tape, and the friction pulls the board up and levels it out.
Physics can explain why simple, or not so simple, things in our world work.