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Activities in High-Speed Photography

 

The Bouncing Ball -- A Challenge

 

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Goals

  • to investigate the motion of a projected, bouncing ball
  • to devise your own approach to the investigation rather than following step-by-step instructions
Introduction

 

This problem requires you to use what you already know about projectile motion and energy to investigate the motion of a bouncing ball. At first glance, it will seem as if insufficient information is given, as the scale of the photograph is not known and the surface on which the ball bounces cannot be seen. Consider yourself a Physics detective for this problem and come up with some winning strategies.

 

Click on the play button to see the ball bounce.

Right click on the clip above and select Save Target As (or Save Link As).  Save the movie to your working directory.

Note the following things about the clip:

  • The motion does not appear smooth, because the ball was illuminated by a light flashing at a constant rate of 20.0 s-1.

  • The table on which the ball bounces is not visible. However, the ball's reflection from the table can be seen when the ball is near the table.

You may make the following assumptions:

  • The table on which the ball bounces is horizontal.

  • The plane of the ball's motion is vertical and is also parallel to the film plane of the camera.

  • The magnitude of the gravitational field is 9.80 N/kg.

  • If you think other assumptions are needed, consult with the instructor.

The Problems
  1. The photographer ... shame on him ... forgot to record the diameter of the ball. Deduce the value of the diameter as accurately as possible. You'll need the scale factor that you obtain in solving this problem to complete the next one.

  2. What percentage of the total mechanical energy is lost by the ball from one bounce to the next? Compare, for example, the total mechanical energies at the highest points of the two bounces. Based on this, predict the height of the third bounce. State any assumptions that you make.

Data Recording

 

It's important to make a clear and comprehensive accounting of your work. Keep a running record of what you're doing, including dead ends and wrong turns in addition to successes. Your lab journal should provide evidence of solid scientific methods and reasoning.

 

As always, give your files unique names. Provide documentation in a text box in your Graphical Analysis file. Include partners' names, filenames, and any other information you think relevant. Write partners' names and filenames in your data book, too.

 

The Tools

Formulate a plan for solving your problem. Of course, you may see ways to improve your plan as you progress through the solution. Use the video analysis and graphical analysis tools at your disposal.

 

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