# Sophie Duncan lays down some rules for testing response times

23rd January 2004 at 00:00
This "quick reactions" experiment tests students' responses and introduces the concept of a fair test, while at the same time having some fun.

The experiment involves dropping a ruler and measuring the time it takes to catch it. Pupils need to convert distance dropped into time taken, using the simple formula given below. Primary children can use the conversion table instead.

Pupils work in pairs with the tester holding the ruler at the end with the highest numbers. The test subject places their hand around the bottom of the ruler, making sure they are not touching it. The tester drops the ruler and the subject tries to catch it as quickly as possible. This should be repeated several times to determine the average speed taken to catch the ruler.

The subject should have no warning that the ruler is about to be dropped.

Therefore the tester should drop the ruler within 10 seconds of starting the test, but sometimes doing it immediately and sometimes waiting longer.

Compare different people's response times. Who is the fastest? Make a graph showing all the results. What was the average time? Does age make a difference? Compare with other classes' times. Does it make a difference if it is the morning or afternoon, and if you have just eaten or not? Repeat the experiment and see if you can improve your response time.

To work out the response time, you need a formula that gives the distance travelled by an object in a given time. This is determined by g, the acceleration due to gravity, which is 980cm per second squared. Distance, d (in cm), is equal to a half times g, times the response time, t (in seconds), squared. d = 1Z2 x g x t2. Therefore t = C2dZg The following table gives the time for each distance

Sophie Duncan is project manager for science at the BBC

www.bbc.co.ukscience

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