Blog 6: Collisions

This weekend my friends and I decided to have a friendly volleyball tournament.  I was super excited because even though I'm horrible at volleyball, I knew I'd see a lot of examples of momentum and collisions that I could blog about!  In this picture you can see the Bret (left) has hit the ball toward Sean (in the red) who is trying to block it.  The volleyball's momentum is equal to its mass times its velocity.  After Bret hit it, the ball then collided with Sean's hands and bounced back towards Bret.  A bouncy collision! The collision created an impulse which is equal to change in momtum or force times mass.  The ball experienced a large change in momentum so it its impulse must have been pretty big.  Because the time that the ball was in contact with Sean's hands was extremely short, that must mean the the force was very large (J=F  t ) .  Ouch, his hands must've hurt after this from all the force...

Blog 4: Energy, Work and Power

These are pictures of my friend Allie (top) and me (bottom) climbing trees.  The act of climbing a tree incorporates many physics concepts that we have learned about: energy, work and power.  Allie and I are gaining potential energy (mgh) as we climb the tree.  The higher we climb, the more potential energy we have because our h is greater. However, if when we both reached the platform and had the same height, I had more potential energy because my mass is greater.  This also means I did more work.  Work equals the change in energy and since our kinetic energy at the bottom and at the top is 0, then the change is kinetic energy = 0, so work can be calculate by the change in potential energy.  Since I ended up with more potential energy, I did more work.  I also climbed up the tree WAY faster than Allie, so I was also more poweful.  Power is calcuated by dividing work done by the time it takes to do the work.  Doing a lot of work in a short amount of time makes something very powerful.  Therefore because I did more work AND did it faster, I was definately more powerful than Allie.

Once we climbed up to the platform, we ziplined down.  We could calculate the speed at which we ziplined down by using the conservation on total energy.  Because out kinetic energy on the platform = 0 and out potential energy at the end of the zipline = 0, our potential energy (mgh) at the platform would equal our kinetic energy (1/2mv^2) at the bottom.  Solving for v would tell us how fast we were going.