Reaction Time

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Do you have cat-like reflexes? How can you measure your reaction time?

The "How To" From Science-U

You Will Need:

  • Ruler
  • A friend or family member as the test subject


  1. Stand over the test subject with your arm stretched out, holding the ruler with your thumb and forefinger. Put the beginning (end that starts with zero) of the ruler right between the test subject's open fingers.
  2. Without telling the test subject that you're going to do it, drop the ruler and the test subject catches it as quickly as they can.
  3. Measure the distance on the ruler by recording where the test subject grabbed it.
  4. You can use the chart below to convert the distance to reaction time. Reaction time conversion chart
  5. Use the graph below to graph your data to see trends.
  6. Change different variables to see what might cause reaction time to be faster or slower.

For educators and parents - How to guide young learners in science:

  • Inquiry-based learning (IBL) is a teaching approach that is fundamental for the development of higher order thinking skills (summarizing, analyzing, evaluating, creating). It puts the student in the driver's seat and promotes learning through engaging student-based investigations, following the same process used by scientists.
  • IBL begins by posing a question, problem, or scenario rather than simply presenting facts or a standard method to solve a problem. The learner is actively engaged and investigates concepts to reach authentic meaning.
  • The IBL process can vary, however the basics are as follows:

1. The student creates a testable question of their own.

2. The student obtains supporting evidence to answer the question by making observations, doing research, collecting data through an experiment, changing variables from a previous experiment, etc.

3. The student explains the evidence collected.

4. The student creates a claim (explanation) and justifies it using evidence form the investigation.

5. The student creates predictions for future investigations.

  • Recording information during the IBL process is also important to promote science literacy. The following chart is a helpful tool to guide students through the process.

Guided inquiry map

Questions to ask:

  • If the ruler falls farther, does that mean you have slower or faster reaction time?
  • Do people with different ages have different reaction times?
  • Does practicing the ruler drop improve reaction time? Why or why not?
  • Does your reaction time change depending on time of day (i.e. as soon as you get up in the morning, right after lunch, right before bed)
  • Does using your right hand vs. left hand alter your reaction time? Why or why not?

The science behind it:

  • Your eye sees that the ruler has been dropped. Signals race form sensory neurons along the optic nerve from the eye to the brain. The brain then sends off the message through motor neurons down the arm to tell the muscles in the hand to close and catch the ruler.
  • Reaction time depends on eyesight and the speed of the signals that travel from your eyes to your brain and from your brain to your hand.


  • Teaching Great Lakes Science (
  • Planet-science (!.aspx)
  • Partners for Outreach in Informal STEM Education (
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