Air Hockey Collision

Have you heard of the games air hockey and pool?  Think, what do they have in common.  My physics teacher might say that they both include elastic collisions, meaning two objects hit each other then move apart after contact.  This is different from inelastic collisions like a car accident where two objects hit each other then move connected together.  Inelastic collisions can happen between two hockey pucks on an air hockey table or two balls on a pool table.  In class, we learned that after collision both objects' momentum vectors combined create the same momentum before and after the collision.  We also learned that as the balls/pucks move away they move at a 90 degree angle from one another, that is unless it acts like a pendulum where one stops completely and the other moves straight forward.  To learn more about the physics in pool watch: https://www.youtube.com/watch?v=toFFvsMeUqg.

To test all this out we brought in an air hockey table and took a video of the two pucks colliding and splitting off.  As the pictures above of our experiment show, there was a grid we used to find the distance that the puck moved as well as a timer with the video.  Using these we could find the velocity of the two pucks as well as the direction, both before and after.  Using the momentum equation, P=mv, and the information we gathered including the mass of the pucks, we were able to find the momentum of the pucks before the elastic collision, and both vectors after.  When attaching the vectors together they showed the same initial and final momentums in the system.

Block Slide

Well I'm back for the end of the third quarter blogs again, and I'm starting with an interesting experiment called the "Block Slide."  The basis of this was to learn about energy and how energy works in a system and how it can be lost to friction.  We started with a flat ramp with a rubber band strung across and a block alongside it.  My group's objective was to figure out how far to pull back the rubber band to fling the block so it could just hang off the edge of the ramp.

We were able to find some information just by measuring, including the distance from the edge to the rubber band, the spring konstant in the rubber band, the mass of the block.  From there our group was able to work with equations until we found the coefficient of friction.  Then with the coefficient of friction we found the force of friction on the block which in turn allowed us to find the unbalanced force then the acceleration.  With the acceleration of the block and the distance away, and knowing that the ending speed is 0, more equations helped us find the starting velocity.

Once all these elements were figured out, we knew that we had to somehow find how far to pull back the rubber band to give the block enough energy to give it the same initial velocity it needs to reach the edge of the ramp.  To do this we had to move to energy equations.  This was what was new for us at the time.  We learned that the energy as it moved from elastic to kinetic had to be the same quantity.  Therefor, using the equations for kinetic energy, E=1/2mv^2, and elastic energy, E=1/2kx^2, and setting them equal to eachother, we plugged what we knew and were able to find x in the elastic equation.  X stood for the distance stretched for the rubber band and with that we were able to test out and see if it worked.

As you can see from the video, we were able to slide the block just over the mark where we had planned.  Through all the work, we learned how energy works in a system like this and can be used to plan out the motion of an object.