Measuring Reaction Time with a Ruler: The Ruler Drop Experiment

I’m Ken Kuwako, the science trainer. Every day is an experiment.

Measure Reaction Time with Everyday Items! A Simple Experiment for the Classroom and Home

When discussing topics like “the speed of chemical reactions” or “nerve impulse transmission” in class, students often ask simple questions like, “How do you actually measure that speed?” or “Is there really a difference?” This [reaction time experiment] is the perfect way to answer those questions.

What’s more, you don’t need any special equipment. All you need is a ruler and a human hand. You can do it with items found in any classroom, and setup is a breeze. It’s a great activity for students to do together, allowing them to discover their own “reflexes” and “reaction time.” It’s truly a first step toward “scientific self-awareness.”

This experiment is perfect for introducing or supplementing topics like “chemical changes and properties of matter” or “the functions of living organisms (nervous and muscular systems)” in middle school. It can also be adapted for cross-curricular activities with home economics or health and physical education.

What you’ll need

• A ruler (30cm or longer is ideal)

• A partner to help you

Experiment Procedure

First, place your dominant hand (the one you use most often) with your thumb at the 0cm mark of the ruler. Have your partner hold the ruler from the top. Then, your partner will drop the ruler! As soon as you see the ruler fall, try to catch it as quickly as you can. Note where your thumb is when you catch it and record that distance.

Repeat this four times and find the average of the recorded distances.

Calculate Your Reaction Time!

Now, let’s figure out your reaction time from the distance you measured on the ruler. For example, if you caught it at 22cm, you can use the conversion chart below (calculated from the free-fall equation) to find that your reaction time is approximately 0.21 seconds.

The conversion chart is here.

https://docs.google.com/spreadsheets/d/1htl5-sBZ4feMomMj9ZefMNwM0f065_eQrJwp5F9m1gU/edit?usp=sharing

In a real class experiment, the average reaction time for the entire class was an amazing 0.19 seconds! Everyone had pretty fast reactions.

In another class, the average was 0.20 seconds.

Experimenting with Sound-Based Reactions!

What’s more, you can also test your “reaction time to sound,” not just sight. The procedure is almost the same, but the person catching the ruler closes their eyes, and the person holding it gives a verbal cue like “Go!” Try to catch it the moment you hear the sound.

When you actually try it, you’ll often find that your reaction time to sound is faster than your reaction time to sight. The brain’s response time to sound is said to be about 0.1 seconds, which is also relevant in sports. In track and field, starting in less than 0.1 seconds after the sound of the starting pistol is considered a “false start.”

Conclusion

So, what did you think of this experiment? Just by measuring your own reaction time using your eyes and ears, you can experience the speed of your brain and body. It’s a fun and interesting experiment. Try competing with your friends and family! I hope that while doing this experiment, you feel that science is fun and accessible.

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