Reaction time required practical

Aim: To investigate how a factor such as practice or caffeine affects human reaction time using a ruler drop test.

Variables

• Independent: The factor being tested, for example caffeine intake or the number of practice attempts.
• Dependent: Reaction time, found from the distance the ruler falls before it is caught.
• Control: The hand used to catch the ruler (dominant hand); Starting position of the ruler (zero mark level with the top of the thumb); Distance between thumb and finger before the drop; Same person dropping the ruler, with no warning of when it will fall

Equipment

• 30 cm or metre ruler
• Chair and table
• Stopwatch or clock to time any rest periods
• Conversion table or graph linking distance fallen to reaction time
• Optional: caffeinated drink such as cola

Method

1. The person being tested sits with their forearm resting on the edge of a table and their dominant hand over the edge.
2. A partner holds the ruler vertically so the zero mark is level with the top of the tester's thumb and index finger, which are held a set distance apart.
3. Without warning, the partner lets go of the ruler.
4. The person catches the ruler as quickly as possible between their thumb and finger.
5. Read and record the distance in cm at the top of the thumb.
6. Repeat at least five times and calculate a mean distance.
7. Change the independent variable, for example have a caffeinated drink and wait about ten minutes, then repeat the test.
8. Convert each mean distance into a reaction time using the conversion table.

Safety

• Anyone with a heart condition, who is pregnant or who is sensitive to caffeine should not drink caffeinated drinks.
• Limit the amount of caffeine consumed and do not drink anything in a laboratory; carry out this test in a classroom.
• Take care not to drop the ruler onto feet or poke anyone with it.

Results and calculations

Record each distance in a table, calculate the mean for each condition and convert to reaction time (a shorter distance means a faster reaction). The time can be calculated using t = √(2d ÷ g) with d in metres and g = 9.8 m/s², and results can be compared on a bar chart.

Common mistakes and improvements

• The catcher anticipating the drop; vary the time before release so it cannot be predicted.
• Reading the ruler from the wrong position; always read at the top of the thumb at eye level.
• Improvement caused by practice masking the effect of caffeine; allow some practice drops before recording, or test different people in each condition.
• Human reaction and reading errors; repeat many times and calculate a mean, or use a computer-based reaction timer for more precise readings.

Exam tips

• Identify the independent, dependent and control variables, and explain why it is hard to control variables such as tiredness or caffeine already eaten that day.
• Explain the stimulus-response pathway: receptors in the eye, sensory neurone, CNS (brain), motor neurone, effector muscles in the hand.
• Explain that this is not a reflex because the response is conscious and involves the brain.
• Calculate means and ranges and comment on repeatability; suggest using a larger sample of people to make conclusions valid.