Momentum Changes in an Explosion

 To study momentum we are going to do a simple impulse experiment. Two carts, one having an internal ring, compressed and held, are put together in the center of the floor. The spring release can be tapped and the spring will push the carts apart. The velocity of a cart multiplied by the cart mass is the cart momentum.

 As we are interested in comparing velocities we will use a simple method. Since the cart wheels are ballbearing skate wheels, the frictional losses should be low. So a cart, after the push by the spring, should move with nearly constant velocity across the table to hit a brick acting as a bumper. Its velocity is d/t. If we start the carts from some table position so that the carts hit the bumpers at the same instant (only one bump is heard) then time is eliminated from the calculations.

 Try this method of comparing momenta by finding the 'one bump' starting distances for both the unloaded carts. Only press the spring in to the first notch. The cart masses are nearly equal. What would you assume for the ratio of velocities?

 Now that you know how it works with equal masses, how will it work with unequal masses? To find out, repeat the experiment with one, two, and three books on the second cart. Find the 'one bump' distances in each case. (Don't forget to allow for cart length.) Use a 'book' as the unit of mass. Is there a pattern to these values? What would happen if you used the second spring notch? Could you discover the actual increase in force by doing so (and if so, how)?

 Force, Mass, and Acceleration

 This lab will study the motion of a cart which is being pulled by constant force. To apply a constant force to the cart you will use a rubber band stretched to a constant length. Practice pulling the loaded cart along the ground while keeping the rubber band stretched to a constant length over a 0.5 m course. One partner should hold the cart while the other extends the band. The partner holding the cart then releases it.

 Start the experiment with four books on your cart and one rubber band. Time with the stop watch a run of the cart through 1.0 meter marked course (pulled with a constant force). Calculate the acceleration by dividing the 1.0 meter by the time (actually giving you the average velocity) and then by dividing by the time again to get acceleration. Then decrease the number of books by one and repeat (and continue till you have no books or are not able to maintain a constant force). Next repeat the experiment with two and then three rubber bands, again starting with four books and decreasing the number of books. Record again the setup the acceleration. Note which overall setup produces the greatest accelerations. (hint: how does acceleration depend on the force -- how does  acceleration depend on the mass) Note that you are looking at net force only. What other forces are in play in this experiment?