# Ruler Drop Test for Reaction Time

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• 0:04 Introduction to the Experiment
• 1:07 Materials & Steps
• 2:56 How It Works
• 4:20 Lesson Summary
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Lesson Transcript
Instructor: Wendy McDougal

Wendy has taught high school Biology and has a master's degree in education.

In this physics lab, we will be exploring the relationship between time, distance, and acceleration by doing the ruler drop test. The purpose of this lab is to calculate your reaction time based on the amount of time it takes to catch a falling ruler.

## Introduction to the Experiment

Let's take a quick second to go through the basics of this experiment before we get into the steps of completing it.

 Goal To determine your reaction time by using the ruler drop test and a mathematical equation Age Middle school Time to complete Approximately 1 hour Safety concerns Use a wooden ruler instead of a metal one in case it is dropped

Have you ever been in a situation where you had to act quickly before having the chance to think? For example, imagine that an expensive vase is about to fall off the counter next to you. Are you able to react quickly enough to reach down and catch it? You may think so, but you probably don't want to test this idea with breakable vases.

In this physics experiment, you will measure your own reaction time, or the speed with which your body reacts, using nothing but a simple ruler and a little math. Your partner will drop a ruler, which you will try to catch as fast as possible with your fingers. If you act quickly, the ruler will only fall a short distance. By using a mathematical equation that relates distance, acceleration, and time, you'll determine just how speedy you really are.

## Materials & Steps

For this particular experiment, you're actually only going to need a basic measurement ruler and you'll need to create the following data tables:

1
2
3
4
5

Partner Attempt Distance
1
2
3
4
5

Now, in terms of steps to complete this experiment, follow along with these:

1. Find a partner to work with.
2. Sit down at a table or a desk, with your forearm resting on the table and your hand coming out over the edge.
3. Your fingers should be open and ready to catch the ruler.
4. Have your partner hold the ruler with the bottom edge level with the top of your hand. Use centimeters for your measurement, with the 1 cm end pointing down.
5. Your partner should release the ruler between your fingers at an unanticipated moment.
6. Catch the ruler as quickly as possible.
7. Record the number on the ruler at the location where it was caught. Use the number closest to the middle of your thumb at the place where you caught it.
8. Repeat this five times.
9. Switch places with your partner and repeat steps 2-8.
10. Find the average distance for your five drops.
11. Calculate your reaction time using the following physics equation:

where y = the average distance the ruler fell in cm, and g = the acceleration of an object due to gravity, which is 980 cm/s2, normally measured as 9.8 m/s2.

If you need to do some troubleshooting, be sure to perform this experiment in a location without noise or distractions. Also be certain to drop the ruler from the same height each time to keep other factors consistent.

Now you can consider the following discussion questions related to your experiment:

1. Were the points at which you caught the ruler fairly consistent each time?
2. What are some factors that could affect your reaction time?
3. Is there any way you could improve your reaction time?

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