Reaction Time

Reaction time investigation

This investigation is really about our senses and how we receive information and act upon it. There are some good opportunities for the development of practical experiments using simple materials and for extended work involving circuits and datalogging.


Hold a pencil at one end by finger and thumb and allow to hang down vertically.

Hold finger and thumb on the other hand ready at the bottom end of the pencil to catch as you release it.

Release and catch.

Since you are in control of the release of the pencil then you are ready for it and can easily catch it before it has travelled very far.

Picture1 pub hand

Now ask someone else to act as the catcher.

Take your time with the release and distract by talking so that the catcher is caught unawares.

They will most probably miss completely.

Discuss and repeat to get everybody fully aware of what is happening.

Class practical activity

Class divided into pairs and spend several minutes trying out the simple reaction time experiment.

What have we found out?

  • Practice improves ability to catch the pencil.
  • Your partner may be better than you at catching the pencil.
  • Some people catch the pencil when it has fallen only a few cm.

Encourage questions.

Does everyone have the same reaction time?

Why is reaction time important?

If our reaction time was very slow what consequences might there be?

Could our other senses be involved in our reaction time?

What other examples are there from the animal kingdom relating to reaction time?

How do you know if your partner has a faster reaction time than you?

Is a pencil the only way to measure reaction time?

Can a stopwatch be used?

Scientists try to find out the answers to questions by performing experiments in which they can measure things.

The measurements can be recorded and compared and in this way we can see if something is changing or staying the same.

We need a better way of measuring reaction time.

Discuss ways of improving the experiment.

car crash
cat stalk duck


We use are eyes to see when the pencil is released.

As soon as we see it move we grab to catch it.

Our brain receives the information from our eyes, decides what to do and tells our fingers to close.

This process takes a short length of time.

We call it our ‘reaction time’.

Different people have different reaction times.

A stopwatch can measure time accurately yet it isn’t very useful in this experiment. why?

The falling pencil works quite well but we have to compare how much of the pencil has passed your fingers before you catch in order to compare your ‘time’ with someone else.

The pencil doesn’t have any marks to allow a measurement to be made.

A ruler works better because we can see on the scale how many cm of ruler has passed before we catch it.

A ruler lets us measure reaction time not in seconds but in ‘cm of ruler’!

Once we can measure and record we can study the results, make comparisons and decide what to do next – this is what ‘investigating’ is all about.


Displaying our results

We could use a results table as follows:

Eg. If John had 5 tries and wrote down how many cm of ruler had passed each time.


Try number

Number of cm.











Then we compare Sarah when she tried.


Try number

Number of cm.












1. What happened to John’s reaction time as he had more tries?

2. What happened to Sarah’s reaction time as she had more tries?

3. Who improved the most from the first to the fifth try?

4. Who had the fastest reaction time?

5. What do you think might happen if Sarah has more tries?

6. What have you found out about reaction time so far?

7. What else would you like to find out about reaction time?


How can we compare the whole class in our reaction time investigation?

  • We could make separate results tables for each person then compare.
  • We could make one large results table containing all of the ‘data’ and this would make comparison easier providing we design the table properly.
  • We could try an alternative way of doing the experiment which makes it easier to display and understand the results.

An alternative way of performing the reaction time experiment.

Identical paper or card strips are used instead of a ruler and each one can record 1 or more tries.

If 1cm squared paper is used then we can easily record our results in cm or even ‘halves of a cm’.

reaction strip grid vert

You could write the person’s name at the top of the strip.

Where do we measure ‘to’ ?

The strip is held and dropped as before.

How will you know where to measure after the strip has been released and caught?

How will you know which way up the strip was!

How will you remember who the strip belongs to!


Use a pencil to draw around the thumb or finger at the point where the strip is caught.

Measurement starts ‘from’ the bottom.

Every member of the class can have their own strip and record 5 tries.

The best result could be taken as the one chosen for comparison with the rest of the class and that thumb mark could be highlighted in a bright colour to make it stand out.

What next?

The paper strips are then lined up side by side to be compared.

They can also be rearranged to see if certain trends exist.

Finally they can be stuck onto a background to produce a graph if required.

What might we be able to find out from our investigation?


Who has the fastest reaction time in the class?

Do boys have better or worse reaction times than girls?

Do sporty people have the fastest reaction times?

Do people who play video games have the fastest reaction times?

Does the oldest person in the class have the fastest reaction time?

Do children have faster reaction times than grown ups?

If you try the reaction test every day for a week will your reaction time improve?


Can you think of any other things we could investigate to do with reaction times and our senses?

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