Ouch!

Don't worry, nothing is hurting me. That was my reaction to the few examples of Physics that I noticed at this Saturday's Football game at Aloha Stadium. This game was full of many interesting happenings. First there were the two fifteen yard penalties, one on each team, that put us right back where we started, and there were some pretty far thrown flags (none of those "straight to the ground flags," these must have traveled fifteen or twenty yards!). But main examples of Physics that I noticed were the completely inelastic collisions between people, completely inelastic collisions between the ball and the net behind the posts, and the probably inelastic collision between the ball and the soft orange post at the corner of the end zone.

First, the completely inelastic collisions: One of the football players ran towards another player (who may have had the ball, I can't remember), and tackled him. The first player had initial velocity, where as the second player had either none or very little velocity. After the collision, both players went down together, with a common velocity. Their total momentum was the same before and after the collision, although their kinetic energies were definitely different, considering that their uniforms are meant to absorb energy, and I'm sure there was a pretty loud sound as a result. The collision between the extra point kick ball and the net was completely inelastic as well. Ball had initial velocity, whereas the net did not. When they collided, both the ball and the area the ball hit moved with the same velocity. However, the tension on that section of the net by the rest of it caused the net and the ball to come to a stop, leaving weight as the only force acting on the ball (ignoring air resistance), thus allowing it to fall at about -9.8 m/s^2.

And now for the inelastic collision that I tried to diagram above. (Why do I keep forgetting to bring a camera to football games?) I am not sure if the trajectories are correct, but I tried to think about where the ball and post might have gone, and I think they are probably pretty accurate (unless the shape of the football made it go somewhere else). As the ball came in, with it's initial x and y velocities, and hit the post at rest, it transfered some of its momentum to the post, giving it x and y velocity as well. The combined momentum before and after collision of these two objects is the same, but their kinetic energies are very different, as the ground at Aloha Stadium is soft, the post is soft, and they probably let off a dull "phfff" sound. Unfortunately, I had no camera to analyze the motion on Logger Pro, so I can't include exact velocities, angles, or masses(without massing the ball and post, to which I don't have access). That would have made an interesting Physics experiment!