Test Your Reaction!
What You'll Need

  • A ruler that's 12 inches (30 cm) long
  • A friend
  • Reaction time chart (copy this chart on a piece of paper or index card)
chart for recording reaction times for 2 different people

What To Do


Your friend picks up the ruler with the thumb and index finger.

Make sure that your friend holds the ruler at the end with the highest measurement (12 in) and let it hang freely.

ruler dangling from a hand

Hold your arm in front of you. Open up your hand and spread your fingers.

Your friend positions the dangling ruler above your hand. Make sure that the bottom edge of the ruler is even with the top of your spread fingers.

one boy holding a ruler from the top while a second boy has hand at the bottom waiting to catch it

Get ready! Your friend will release the ruler without warning, letting it slip downward.

The moment you see the ruler released, quickly close your hand.

ruler caught by hand

Still holding the ruler, look at where the top edge of your hand meets the ruler. Record this "measurement" in the Reaction Time Chart.

recording measurements in a chart

Try this two more times.

Then figure out the average by adding the three measurements and dividing the sum by three. This is the average distance that the ruler dropped before you stopped its fall.

ruler caught in a hand

Switch roles with your friend and repeat Steps 1 to 5 to find out who's quicker. (The lower the number, the faster you are.)

Practice makes perfect. Try this activity a few more times to improve your reaction time.

chart filled in with times and measurements