B10 RP Required Practical: Reaction Time

A free GCSE Combined Science: Trilogy lesson for AQA (8464) from OBA School: aQA required practical: planning and carrying out an investigation into the effect of a factor on human reaction time. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Plan a valid investigation into a factor that affects reaction time, with a hypothesis
• Identify independent, dependent and control variables, hazards and ethical issues
• Convert ruler-drop distances into reaction times and calculate means
• Present results in a suitable chart and evaluate the method

Key words

• Reaction time: The time between a stimulus and the response to it.
• Hypothesis: A testable idea, e.g. “reaction time is shorter for a sound cue than for a visual cue”.
• Valid: The results answer the question, because other variables were controlled.
• Precise: Repeat readings are close together, with little spread about the mean.
• Accurate: A reading close to the true value.
• Ethics: Keeping the investigation safe and fair for the people taking part, with their consent.

Aim, hypothesis and variables

Aim: to find out how one factor affects reaction time. Catching a falling ruler is a conscious action, not a reflex: receptors in the eye (or ear) detect the stimulus, the brain decides, and impulses travel along motor neurones to the hand muscles.

Factors you could test: type of cue (seeing vs hearing), practice, dominant vs non-dominant hand, caffeine, distraction (music, talking), tiredness or time of day.

• Independent; Example: visual cue vs sound cue Type of cue: watching the ruler, or eyes closed and listening for a word
• Dependent; Example: visual cue vs sound cue Reaction time (from the distance the ruler falls)
• Control; Example: visual cue vs sound cue Same person catching and dropping; same ruler; same hand; same starting position and finger gap; no warning; same time of day; no caffeine beforehand

Method: the ruler-drop test

• 1. The person being tested rests their forearm on a table, with the hand over the edge.
• 2. The tester holds a 30 cm ruler vertically, with the 0 cm mark level with the top of the thumb. Finger and thumb are open but not touching the ruler.
• 3. Without warning, at a random moment, the tester drops the ruler. The person catches it as quickly as possible.
• 4. Read the distance at the top of the thumb to the nearest 0.5 cm.
• 5. Repeat at least 5 times. Then repeat with the other condition, e.g. eyes closed while the tester says “now” as they let go.
• 6. Convert each distance to a time and calculate the mean for each condition. Swap roles and repeat.

Safety and ethics: participants must agree and can stop at any time; keep results anonymous. If testing caffeine, use a small amount and exclude anyone with heart problems, who is pregnant or who is sensitive to caffeine. Keep drinks away from electrical equipment and mop up spills.

Processing results

A falling ruler speeds up, so time is not proportional to distance. Use a conversion graph or table, or this equation:

Formula: reaction time t = √(2d ÷ g) with d in metres and g = 9.8 m/s²

Worked example: visual vs sound cue

Catch distances (cm). Visual: 17, 19, 18, 20, 16. Sound: 14, 12, 15, 13, 13.
Means: visual = 90 ÷ 5 = 18.0 cm; sound = 67 ÷ 5 = 13.4 cm.
Times: t = √(2 × 0.180 ÷ 9.8) = 0.192 s; t = √(2 × 0.134 ÷ 9.8) = 0.165 s.

Answer: Visual 0.192 s; sound 0.165 s, so this person reacted faster to sound

Evaluating the method

• Catching improves with practice; Improvement Give practice drops first, or alternate the conditions
• The person can guess when the ruler will drop; Improvement Vary the time before each drop; no countdown
• Results differ a lot between people; Improvement Use the same person for both conditions; test many people and compare means
• Ruler read only to 0.5 cm; Improvement Use a computer reaction timer (records in ms)
• Repeat results spread out (not precise); Improvement More repeats; identify and remove anomalies

Repeatable results are similar when you repeat the test; reproducible results are similar when another group repeats it.

Common mistakes

• Calling the ruler catch a reflex. It involves the conscious brain.
• Treating time as proportional to distance. Use the graph or equation.
• Forgetting to convert cm to m before using the equation.
• Drawing a line graph for a categoric variable. Use a bar chart.

Revision questions

Try these, then check your answers below each one.

Question 1. A ruler-drop test is shown. Before the drop, the 0 cm mark was level with the top of the person’s thumb. Use the diagram to find how far the ruler fell before it was caught.

Answer: 14 cm

Working: The top of the thumb is at the 14 cm mark, so the ruler fell 14 cm.

Question 2. A student investigates whether listening to music affects reaction time using the ruler-drop test. What is the dependent variable? (Choose from: Whether music is playing, The distance the ruler falls (reaction time), The length of the ruler, The hand used.)

Answer: The distance the ruler falls (reaction time)

Working: The distance fallen is measured and converted to a reaction time. Music is the independent variable; the hand and ruler are control variables.

Question 3. True or false? The ruler should be dropped at random times, without a warning or countdown.

Answer: True

Working: Random timing stops the person predicting the drop, so the test measures true reaction time.

Related lessons

• Previous lesson: B10.3 Reflex Actions
• Next lesson: B11.1 Principles of Hormonal Control
• In this chapter: B10.1 Principles of Homeostasis
• In this chapter: B10.2 The Structure and Function of the Human Nervous System

Continue in the full course

This lesson is section B10 RP (AGCSC1004) of our free GCSE Combined Science course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Combined Science course.