Why have I never looked at curling before? You know curling. It's that sport (olympic sport) where people slide rock like things on ice and collide with other rock like things. Yes, there are more to the rules than that but that is all you need to know. Here is the particular clip I am looking at.
http://www.youtube.com/watch?v=iIjjZL8bfkk
So, what am I going to do? I am going to look at the velocity of the stone before the first collision and the velocities of the two after the collision. Of course, Tracker Video is perfect for the job.
Here is the motion of the first stone (which I am calling A) before and after the collision.
This gives an initial x- and y-velocity of:
After the collision, it has a velocity of:
Similar plots for stone B (the one that was hit).
With a velocity of:
So, what to do now? I could look at the momentum. If there are no external forces (or they are small and can be ignored), then the change in momentum of stone A will be the opposite of the change in momentum of stone B. The reason is that stone A exerts a force that is the same magnitude but opposite direction on B that B exerts A. Since these forces are the same magnitude and for the same time, the change in momentum of the two objects is the same (but opposite direction).
Momentum might not be all that easy to look at in this case. According to Wikipedia, the stones have a mass from 17 - 20 kg. So, I don't really know the masses of these objects. Let me just call them mA and mB. This means that:
In the x-direction, this gives:
And in the y-direction:
Ok, both the x- and y-directions should have the same ratio of masses. I guess my data wasn't so great. Perhaps I could try finding a high definition version of this video.
But what about kinetic energy? Was the kinetic energy the same before and after the collision? Just assume the masses are the same. The real question is: should KE be the same before and after? Well, if it were a completely elastic collision then the total KE should be the same before and after. I will let you check that.
