Reaction Time

So You Want to Do a Project about Reaction Time!

Purpose

To determine how to measure reaction time.

Materials

• table and chair
• ruler
• helper

Procedure

1. Sit on the chair with your forearm on the tabletop and your writing hand extended over the edge of the tabletop.
2. Ask your helper to hold the ruler so that the bottom of the stick (the zero end) is just above your hand.
3. Place your thumb and index finger on either side of, but not touching, the bottom of the ruler.
4. Ask your helper to drop the ruler through your fingers without telling you when it is going to be dropped.
5. After the ruler is released, try to catch it as quickly as possible between your thumb and fingers.
6. Observe the number on the ruler just above your thumb. Record this number as the reaction distance.

Results

The distance the ruler falls varies with each individual.

Why?

Reaction time is the time it takes you to respond to a stimulus, which is something that causes an organism to react. In this experiment, your reaction time was how long it took you to catch the falling ruler (stimulus). The greater the reaction time, the greater the reaction distance. In this project, the reaction distance is used to indicate the reaction time.

Reaction distance will vary with individuals because when the ruler begins to fall, a message is sent to the brain. Like a computer, the brain takes this input information and, in fractions of a second, sends a message telling the muscles in the hand to contract (shorten or be made smaller by drawing together). The distance the ruler falls varies for each individual depending on the time it takes for these messages to be sorted out by the brain and the output message to be received by the hand's muscles. Nerves, which are bundles of cells, send messages throughout the body. The nerves in the eye start this relay of messages. The first stop is in the largest section of the brain, called the cerebrum. The cerebrum is where all thoughts occur and where input from sensory (having to do with sight, smell, hearing, taste, and/or touch) nerves is interpreted. The cerebrum sends a message (nerve impulse) to another section of the brain, called the cerebellum. The cerebellum brings together all the muscle actions that are necessary to grasp the ruler. Reaction time does not have anything to do with how smart you are; instead, it compares differences in hand-eye coordination.

For Further Investigation

Learning can occur when actions are repeated. Can a person learn to catch the ruler faster and improve the reaction time? A project question might be, How does practice affect reaction time?

Clues for Your Investigation

1. Repeat the investigation 10 or more times and have others perform the experiment as many times.
2. Record the results in a Reaction Time Data table like the one shown.
3. Create a line graph with each person's results plotted in a different color ink.
4. Display the table and graph as part of your project.

References and Project Books

Allison, Linda. Blood and Guts. New York: Little, Brown, 1976.

Beckelman, Laurie. The Human Body. Pleasantville, N.Y.: Reader's Digest, 1999.

Parker, Steve. The Brain and Nervous System. New York: Franklin Watts, 1990.

How the Body Works. Pleasantville, N.Y.: Reader's Digest, 1994.

The Human Body. Brookfield, Conn.: Copper Beech Books, 1995.

Schultz, Ron. Looking inside the Brain. Santa Fe, N.M.: John Muir Publications, 1992.

VanCleave, Janice.janice VanCleave's Animals. New York: Wiley, 1992.

Janice VanCleave's The Human Body for Every Kid. New York: Wiley, 1995.

Wiese, Jim. Head to Toe Science. New York: Wiley, 2000.

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