# Balls Bouncing Off of Surfaces *

 Difficulty Time Required Short (2-5 days)
*Note: This is an abbreviated Project Idea, without notes to start your background research, a specific list of materials, or a procedure for how to do the experiment. You can identify abbreviated Project Ideas by the asterisk at the end of the title. If you want a Project Idea with full instructions, please pick one without an asterisk.

## Abstract

For example, think of hitting a baseball, heading a soccer ball into the net, or hitting a tennis ball with a racquet. Where the ball goes depends on...what? You can set up a simple model to start your investigation. You'll need a marble, a flat piece of wood, a flat piece of cardboard, a pencil, a ruler, a protractor, and a level surface. Lay down the cardboard down on a level surface and set up the flat piece of wood at one edge. The wood will act like a wall, and you're going to roll the marble at it from different angles to see how the marble bounces off. On the cardboard, mark the starting point, the point where the marble strikes the wood, and a point along the marble's path as it rolls away from the wood. Use the pencil and ruler to connect the incoming and outgoing trajectories of the marble to the point where the marble bounced off the wood. Draw a line perpendicular to this point, and measure the angle between the perpendicular line and the incoming and outgoing trajectories. Do this for at least 10 trials at each of several different angles. What is the relationship between the two angles? Now apply what you learned to a real-life sports situation (like heading a soccer ball or hitting a baseball). In the real-life situation, the ball is no longer hitting a stationary target and bouncing off, it's hitting something that is moving. That makes it harder to measure the angles; just remember that what is important is measuring the angles at the point of impact. For a more advanced project, you may also want to consider how the spin of the ball can change its trajectory. You could choose to concentrate only on the spin imparted by the kick, the bat or the racquet, or you may want to get really complicated and consider the spin of the incoming ball as well. (Idea from Wiese, 2002, pp. 31-34. For more advanced explanations, including the effects of spin, see the Bibliography for a book on the particular sport which interests you.)

### MLA Style

Science Buddies Staff. "Balls Bouncing Off of Surfaces" Science Buddies. Science Buddies, 18 Dec. 2014. Web. 27 Apr. 2017 <http://www.sciencebuddies.org/science-fair-projects/project_ideas/Phys_p039.shtml>

### APA Style

Science Buddies Staff. (2014, December 18). Balls Bouncing Off of Surfaces. Retrieved April 27, 2017 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/Phys_p039.shtml

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Last edit date: 2014-12-18

## Bibliography

Wiese, Jim. Sports Science: 40 Goal-Scoring, High-Flying, Medal-Winning Experiments for Kids. New York: John Wiley and Sons, 2002.

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