Teaching Modern Physics - QuarkNet - Fermilab

Conservation of Momentum Lab
Goal:
To perform an elastic collision between two balls and to compare the vector momentum of
the system of two balls after the collision with the vector momentum before the collision.
You need to know that P = M*v and that momentum is a vector. You also need to know the
basic equations of projectile motion.
Part 1 - 1D Collision
1. Clamp the device to the table with “C” clamp. Rotate the end flange to the side so the ball
can roll down the ramp and shoot off into the air without hitting the end flange.
2. Tape a piece of paper on the floor beneath the lower end of the device. Place a piece of
carbon paper over the paper. Drop a metal ball straight down from the lower end of the
device onto a piece of carbon paper that is on the floor. The ball will leave a mark on the
paper. Call this point A.
3. Let metal ball roll down the ramp, off the device and hit the floor. Place a piece of carbon
paper on top of a piece of paper on the floor where the ball hit the paper and repeat the
ball roll. The second roll will leave a mark on the paper at point B.
4. Now rotate the flange back into place and adjust the set screw on the flange. Place the
second metal ball on the recess of the set screw. Adjust the height of the set screw so that
when ball 1 rolls down the ramp and hits ball 2 on the set screw, the second ball flies off
and hits the floor very near [within a centimeter or so] of point B. This ensures that the
collision between ball 1 and ball 2 is an elastic collision. Do not change the level of the
set screw.
5. Measure to three significant figures the distance between the floor and the bottom of the
balls just as the ball flies off the device. Calculate the time the ball is in the air.
Part 2 – 2D Collision
1. Rotate the flange to one side a bit. Place ball 2 on the set screw. Roll ball 1 down the
ramp and it will hit ball 2. Both balls will fly off the apparatus and onto the floor. Notice
about where each ball hits. Place a piece of carbon paper on the sheet of paper on the
floor at these points. Call where ball 1 hits point C and where ball 2 hits point D.
2. Do not change the set screw. Repeat the previous step, but now with the carbon paper in
place. Check to see that points C and D are recorded on the paper.
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