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Reaction Time

Reaction Time

Reaction Time

Reaction times for the driver to stop a car can vary but there is an average value typically. We will use methods to calculate reaction times.

The overall stopping distance of a vehicle, is the sum of the braking distance, and which other distance?

Thinking distance is how far a car travels during the driver's reaction time. What do you think we mean by the term reaction time when we are talking about transport?

Thinking distance and reaction time are different, because time is measured in seconds, and distance in metres. In other words, thinking distance is the distance a vehicle travels during the driver's reaction time.

If a person's reaction time is slower, the thinking distance will be ...

If a ball was flying towards your face, you would react and try to move out of the way. Everyone has a different reaction time. Try to guess the typical values for reaction time.

At your most alert, you might react to the ball flying towards your face faster and move out of the way in time. At other times, you might end up with a ball to the face! Which factors do you think might slow down reaction times?

You can select multiple answers

A slower reaction time means that a driver's thinking distance will be increased. This in turn will increase the overall stopping distance of the vehicle, heightening the risk of crashing.

This explains why it is so important that people don't drive when they are tired, distracted, on drugs or when they have consumed alcohol.


A very simple way to measure your reaction time is to perform a ruler drop test

Sit with your arm resting on the edge of a table, and ask someone to hold a ruler between your thumb and forefinger. Without any warning, the person holding the ruler will drop it, and you should try to catch it as quickly as possible.


When the ruler is dropped, the measurement on the ruler where your thumb and finger catch it provides what information?

A) Your reaction time B) How far the ruler dropped in your reaction time


So that you get an accurate measurement, before the ruler is dropped should you...

A) Make sure that your thumb and forefinger line up with zero each time B) Line your thumb and forefinger up with a different number each time C) Not line your fingers up with any particular number


If you caught the ruler at 2 cm2\space cm, and your friend caught the ruler at 3 cm3\space cm, who do you think has the fastest reaction time? Answer "me" or "my friend".

To make sure a test is fair, you need to keep all variables - other than the one you are testing - the same. When performing the ruler drop test, what could you do to make sure it's a fair test?

You can select multiple answers

A student performed the ruler drop test, and repeated it 5 times to be able to calculate a mean measurement value. His results were 4,6,5,5,6 (cm)4, 6, 5, 5, 6\space (cm). What was the average distance that the ruler dropped during the time it took the student to react?

Using this simple method, you could then investigate and find out how different factors affect reaction time. For example, you could repeat the investigation whilst listening to music, and compare the mean distance that the ruler dropped in your reaction time when there was no music playing.

A student performed the ruler drop test with no distractions, and found that the mean of the distances the ruler dropped in his reaction time was 6.5 cm6.5\space cm . He repeated the investigation whilst having a conversation and calculated a mean distance of 9.2 cm9.2\space cm. What conclusion could you make from these results?

Which other method could you use to measure a person's reaction time?

In an investigation, a student found that his reaction time increased when talking on his mobile phone. If a driver was talking on his mobile phone, how might he be risking the safety of himself and other drivers?