PHYS310 Lab 12 Momentum
Lab 12: Momentum
Experiment 12.1: Conservation of Momentum
In this experiment you will demonstrate transfers of momentum similar to those of the Newton’s Cradle toy pictured in Figure 12.1. The
velocity of a marble after impact depends on the original velocity and the mass of the objects at hand.
1. Fold a sheet of paper in half to create chute for your marbles to travel down.
2. Line up four marbles in the center of the ruler, making sure they are all touching. Set up a barrier so that you can catch your marbles
easily when they leave the ruler.
3. Hold the chute so that the end lies in the ruler’s groove, and let a marble go inside. You want the marble to exit the chute onto the
ruler groove and collide with the line of marbles you set up.
4. Try angling the chute less or placing the marble closer to the ruler to decrease the speed of the collision, noting any difference in the
velocity of the marbles after collision.
5. Increase the speed of the collision and see what happens.
6. Finally, try dropping two marbles at once so that they hit the line as a pair.
1. When one marble hit the end of the line of marbles, how many shot off the other end? Explain why this happens, as opposed to more
than one shooting off.
2. How did the speed of the marble that comes off the end of the line change as you increased the speed of the
marble that travels down the chute? Use what you know about the conservation of momentum to describe
what is happening.
3. What happened when you sent two marbles down the chute?
4. Write down the total momentum for two marbles of mass m both moving at velocity v. What is the kinetic energy?
5. When you drop two balls at once, why doesn’t only one marble come off the end twice as fast? Write down the kinetic energy of one
marble with mass m and velocity 2v and compare this to your answer in Question 4 to check. (Note that we are assuming the collisions
are perfectly elastic, when in reality this is an approximation.)
Experiment 12.2: Egg Drop
When a fragile object is subject to a sudden acceleration, the strain on the material can cause it to break. By increasing the time and
distance over which an object accelerates or decelerates you can prevent damage that might occur otherwise, even if the total change
in momentum is the same. In this lab you will attempt to decelerate a falling egg so that it does not break.
1. Did you come up with a design that prevents the egg from breaking?
2. Why did adding layers of paper work better than one thick layer with the same number of sheets? (Hint: over how much time is the
force applied in each case?)
3. What did you do to improve your apparatus?
4. Explain how a circus net prevents trapeze artists from injuring themselves even after falling from a large height.
5. Why it is important to bend your knees when you hit the ground after jumping from several feet in the air?
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