Test Your Reflexes with a Ruler! Reaction-Time Experiment #1 (Eyes → Brain → Spinal Cord → Hand)
I’m Ken Kuwako, a Science Trainer. Every day is an experiment!
When teaching topics such as “the rate of chemical reactions” or “the speed of nerve impulses,” students often come up with simple but fascinating questions: “How can we actually measure speed?” or “Is there really a difference?” This reaction time experiment is perfect for answering those questions.
Best of all, you don’t need any special equipment. All you need is a ruler and a pair of human hands. Everything can be done with things you already have in the classroom, and setup takes almost no time. Students can have fun working together while discovering their own “reflexes” and “reaction times.” In that sense, it’s a great first step toward developing a scientific understanding of themselves.
This experiment is a great introduction or supplementary activity for middle school lessons on “Chemical Changes and Properties of Substances” or “Functions of Living Things,” particularly the nervous system and muscles. It can also be developed into a cross-curricular activity with home economics or health and physical education.
What You’ll Need
•A ruler (30 cm or longer is ideal)
•A partner to help you
How to Do the Experiment
First, place the ruler with the 0 cm mark level with the bottom of the thumb on your dominant hand—the hand you normally use most.
Have your partner hold the top of the ruler. Then, without warning, have them drop it! As soon as you see the ruler falling, try to catch it as quickly as possible. Check the point on the ruler where your thumb caught it, and record the distance.
Repeat the experiment four times and calculate the average distance.
Calculate Your Reaction Time!
Now let’s use the distance measured with the ruler to calculate your reaction time. Suppose, for example, that you catch the ruler at 22 cm. Using the conversion table below, which is calculated from the equation for free fall, we can see that your reaction time is about 0.21 seconds.
Here is the conversion table.
https://docs.google.com/spreadsheets/d/1htl5-sBZ4feMomMj9ZefMNwM0f065_eQrJwp5F9m1gU/edit?usp=sharing
I actually tried this experiment with one class, and the average reaction time for the entire class was an impressive 0.19 seconds! Everyone had some pretty quick reactions.
Another class averaged 0.20 seconds. Catching a banknote is another fun experiment to try, too!
Test Your Reaction to Sound, Too!
You can also test your reaction time to sound, rather than just visual cues. The procedure is almost exactly the same, except that the person catching the ruler keeps their eyes closed. The person holding the ruler says “Go!” as the signal, and the catcher tries to grab the ruler the instant they hear the sound.
When you try it, you’ll often find that your reaction to sound is faster than your reaction to something you see. The brain is thought to respond to sound in roughly 0.1 seconds, and this is also important when it comes to starting sports events. In track and field, for example, an athlete who starts less than 0.1 seconds after hearing the starting gun is considered to have made a false start.
Wrapping Up
So, what did you think? Simply measuring your own reaction time using your eyes and ears is a surprisingly fun way to experience just how quickly your brain and body can respond. Why not compete with your friends or family and see who has the fastest reactions?
I hope that while doing this experiment, you’ll discover that science can be both fascinating and surprisingly close to everyday life.
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Want to bring the wonder and fun of science a little closer to everyday life? I share easy and enjoyable science experiments you can do at home, along with simple explanations and helpful tips. Feel free to explore the site and see what you can discover!
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