Reaction Time: The Ruler Drop Test

The nervous system helps information travel through your body. It consists of the 5 senses, your brain, your spinal column, and the nerves that connect them all together. Suppose your eyes see a baseball sailing toward your head. They send a message about the approaching ball to your brain. This message travels to a part of your brain called the cerebrum through nerves. Your cerebrum sends this information to the cerebellum, which has to choose whether to move away, duck, or put a hand up to catch the ball. It finally decides that you should catch it—after all, you’re wearing your baseball glove! The cerebellum sends this decision as message through other nerves to the arm and hand, activating the muscles used to catch the ball.

The time it takes from when your eye first notices the ball to when your arm reaches up to catch it is an example of reaction time. Even though stimuli—or changes in your environment that you react to—travel very quickly along your nervous system as messages, your body doesn’t react instantly. Many athletes spend hours practicing to improve their reaction time. In this activity, you will conduct a simple, measurable experiment (the ruler drop test) to study reaction time and determine how it can be improved with practice.

Grade

Fourth Grade

Subject

Science

• Life Science

Problem

How can reaction time be measured and improved?

Materials

• Metric ruler
• One or more volunteers
• Table
• Chair

Procedure

1. Ask your first volunteer to sit in the chair with good upright posture and eyes looking across the room.
2. Have the volunteer place her forearm (the part of the arm from elbow to hand) so it extends over the edge of the table.
3. Ask the volunteer to place her thumb and index (pointer) finger on either side of the bottom of the vertically placed ruler. The number “1” should be on the bottom, the “30” near the top.
4. Let your volunteer practice holding the ruler with those two fingers.
5. Now, ask your volunteer to remove her fingers from the ruler while you continue hold it so that the bottom of the ruler is at a height of 2cm above her fingers.
6. Tell your volunteer that you will release the ruler without telling her. Her job will be to catch it with her thumb and forefinger as soon as she senses it dropping.
7. Drop the ruler. When your volunteer catches it, record the number on the ruler displayed just over her thumb. The lower the number, the faster her reaction time.
8. Conduct several trials with the same volunteer, dropping the ruler from 2cm above her fingers each time.
9. Make sure to record the results for each trial in a table similar to the following:

Volunteer	cm trial 1	cm trial 2	cm trial 3	cm trial 4
Alison
Mack

10. You might consider letting your volunteers have a rest between trials.
11. Repeat the experiment with at least one other volunteer.

Results

Your results will vary depending on technique and which volunteers you used, but you should expect that many of your volunteers will show a slight improvement with practice.

Why?

When we begin to acquire a new physical skill through repetition, our nervous system creates new neural pathways. Here’s an example: when we practice something like catching a ruler over and over again, all the members of that neural pathway (eye, brain, muscles) become more well-connected and efficient. This phenomenon is often referred to as muscle memory. However, no matter how good your muscle memory for this task becomes, it will always take some time for the falling ruler to travel as a message from your eyes to your brain and from your brain to your fingers!

Going Further

Reflexes in response to stimuli are our quickest reactions. One example is when a doctor hits a spot right below your kneecap and you kick before you even consciously realize you’re doing so. One cool question to explore might be whether reflexes and learned motor skills like catching a ruler can enable us to respond to stimuli more quickly in the morning or in the evening. How does the length of time spent awake affect the efficiency of our central nervous system? Why?

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