Reaction Time

How quick do you think you are? With the help of a friend, you can find out.

• Yard stick

• Chair to stand on

• Chair to stand on

Try this to find your reaction time:

1. Have your friend hold a yardstick from the top so
that it is up and down with the bottom several feet above the floor.
Your friend may have to stand on a chair to do this.

2. You hold your fingers opposite the 18-inch mark, but don't touch the stick! Without warning your friend should let go of the yardstick, and you should try to catch it with your fingers.

3. Notice what inch mark your fingers are on when you catch the stick. Subtract this number from 18 or subtract 18 from the number to see how many inches the stick fell before you caught it. Try it several times to see if you get the same answer. Let your friend try to catch it while you drop it. Who has the quickest reaction time?

4. Your reaction time can be determined from the table below:

2. You hold your fingers opposite the 18-inch mark, but don't touch the stick! Without warning your friend should let go of the yardstick, and you should try to catch it with your fingers.

3. Notice what inch mark your fingers are on when you catch the stick. Subtract this number from 18 or subtract 18 from the number to see how many inches the stick fell before you caught it. Try it several times to see if you get the same answer. Let your friend try to catch it while you drop it. Who has the quickest reaction time?

4. Your reaction time can be determined from the table below:

distance dropped | reaction time |

2 inches | 0.10 seconds |

4 inches | 0.14 seconds |

6 inches | 0.18 seconds |

8 inches | 0.20 seconds |

10 inches | 0.23 seconds |

12 inches | 0.25 seconds |

14 inches | 0.27 seconds |

16 inches | 0.29 seconds |

18 inches | 0.31 seconds |

Why do you think it takes time for your fingers to react when your eyes see the stick start to fall? Can you think of reasons the reaction time might be different for an adult and a child? Perhaps you could test your theory with several adults and children.

What’s going on?

Gravity is pulling down on the yardstick at a constant rate. The longer it falls, the faster it goes. By measuring how far the yardstick falls, we can calculate the speed at which it is moving and the time it took you to catch it

Back to the Just for Kids Page

Wonders of Physics

University of Wisconsin

1150 University Ave

Madison, WI 53706

This page updated on Sept. 18, 2007