Advanced Physics: Tennis Ball Collisions
28 January 2003
Prepared by Ann Brandon
Procedure:

Hang a pair of Tennis Balls so that they are level with each other. (Centers
touching)
Tape the ribbon to the pole so that it will not slip.

Place the paper on the table so that the lines cross under the center of
the TBalls.

On the Paper, mark the spot where the TBalls touch.

Pull them equal distances away from each other along the line connecting
them. Mark each "inside" edge with a B {=
"before").

LET GO! They should hit and bounce off. CATCH them
just as they stop swinging out. Mark each "inside" edge
with an A (= "after").

Trial 2: Move the paper  so that the Tballs line up on a
different line. Repeat #4 and #5, but pull them
unequal distances out. Again, mark their starting and stopping
points.

Trial 3: Wrap your tennis balls with VelcroŽ.
Try #4 and #5 again.

Trial 4: Now, pull the tennis balls out, and at an angle to
the line connecting their centers. Again mark the starting point,
and the locations after the collision.

Trial 5 (finally!): Trade your Tballs for a set of unequal
masses and try #4 and #5 again. Note on your paper
with Tball is the heavy one..
Analysis:

The mass of the light Tennis Balls = 1 TB.

The mass of the heavy Tennis Ball = 2 TB.
For the First, Second, Third, and Fourth Trials:

Draw velocity vectors from the B's to the contact points.

Then, ADD these velocities together, TIP TO TAIL, and note their total
[magnitude and direction]. This is the total momentum before the
collision.

Draw the velocity vectors from the contact points to the A's, ADD these
pairs TIP TO TAIL and note their total. This is the total momentum after
the collision.

Be careful with the Third and Fourth trials. The mass after the collision
should be 2 TB. Why?
 Compare the Total Before to the Total After for each of these Four Trials
Trial 5: unequal masses!
 You will need to multiply the velocity of the heavy ball
by 2 to get its momentum (vector). Why?
 Do so. Determine the total momentum of the system of two balls [a vector] before and
after the collision.
 Compare the total momentum before and after for this trial