Advanced Physics: Tennis Ball Collisions
28 January 2003
Prepared by Ann Brandon
  1. 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.
  2. Place the paper on the table so that the lines cross under the center of the T-Balls.
  3. On the Paper, mark the spot where the T-Balls touch.
  4. Pull them equal distances away from each other along the line connecting them.  Mark each "inside" edge with a B {= "before").
  5. LET GO!  They should hit and bounce off.  CATCH them just as they stop swinging out.  Mark each "inside" edge with an A (= "after").
  6. Trial 2Move the paper -- so that the T-balls line up on a different line.  Repeat #4 and #5, but pull them unequal distances out.  Again, mark their starting and stopping points.  
  7. Trial 3:  Wrap your tennis balls with VelcroŽ.  Try #4 and #5 again.
  8. 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.
  9. Trial 5 (finally!):  Trade your T-balls for a set of unequal masses and try #4 and #5 again.  Note on your paper with T-ball is the heavy one..  
  1. The mass of the light Tennis Balls = 1 TB.  
  2. The mass of the heavy Tennis Ball = 2 TB.
For the First, Second, Third, and Fourth Trials:
  1. Draw velocity vectors from the B's to the contact points.
  2. Then, ADD these velocities together, TIP TO TAIL, and note their total [magnitude and direction].  This is the total momentum before the collision.
  3. Draw the velocity vectors from the contact points to the A'sADD these pairs TIP TO TAIL and note their total.  This is the total momentum after the collision.
  4. Be careful with the Third and Fourth trials.  The mass after the collision should be 2 TB.  Why?  
  5. Compare the Total Before to the Total After for each of these Four Trials
    Trial 5: unequal masses!
  1. You will need to multiply the velocity of the heavy ball by 2 to get its momentum (vector). Why?
  2. Do so. Determine the total momentum of the system of two balls [a vector] before and after the collision.
  3. Compare the total momentum before and after for this trial