Launch practical
About 60 minutes
- Set up the bench with the 6 items of apparatus.
- Take the readings yourself, into the results table you draw first.
- Process your results.
- Answer exam questions on your own results, which you mark against the mark scheme.
Runs in your browser: a 3D bench with 2D close-ups of each instrument for exact readings. Nothing to install and no account.
What you measure, and how
One run takes 10 readings. You take every one yourself, the way you would in class.
- On the 3D bench (Fig. 1) you set out the apparatus and read each instrument where it stands.
- In the 2D close-up (Fig. 2) the same instrument is drawn large, from the same run, for an exact reading. It is also how the practical runs on a device that cannot show 3D.
- In your table you write what you read, to the instrument’s resolution, and the notebook checks it against the instrument.
Your eye does the reading. Each volume starts with your eye off level, so the scale lines up with the wrong mark. You move your eye, on the bench or in the close-up, until it is level. Nothing is right by default.
What it shows
t = √(2d / g)
You see the ruler move (receptor: the eye), a nerve impulse travels along a sensory neurone to the brain, which decides to catch, then along a motor neurone to the muscles of your thumb and finger (effectors). Meanwhile the ruler falls from rest, d = ½gt², so the distance it falls before you catch it measures your reaction time. With d in cm, g = 980 cm/s².
Key equation for the exam: No equation to learn: convert the catch distance to a time with the table or equation given..
No equation to learn. A shorter catch distance means a shorter reaction time.
Apparatus
| Item | What it is for | Resolution |
|---|---|---|
| Metre rule | Dropped and caught: the distance it falls measures your reaction time. | 1 mm (read to 0.5 cm at the thumb) |
| Chair and table | Sit upright with your forearm resting on the table. | — |
| Safety goggles | For the person dropping the ruler. | — |
| Conversion table | Converts the distance fallen to a reaction time. | — |
| Results table and pencil | Record every catch as you go. | — |
| Your catching hand and a partner | Your partner holds the rule at the top and drops it with no warning. You catch it with your thumb and first finger. | — |
Method
In our own words, as the Lab runs it. Your school's method sheet may differ in detail.
Your factor
Choose the one factor you will change. Everything else stays the same.
Do: Practice: does reaction time get shorter over 10 attempts in a row? (the AQA handbook’s investigation).
Why: A fair test changes one variable (the independent variable) and measures its effect on reaction time.
Agree how you will workSafety
Your partner agrees to take part and knows they can stop at any time. Write results under a code, not a name, and do not rank people.
Why: This investigation uses people (AT 4: the safe and ethical use of humans). Nobody should feel uncomfortable about a slow result.
Put goggles on the person who drops the rulerSafety
The person who drops the ruler wears safety goggles.
Why: A dropped metre rule can bounce off the floor and up into the face of the person dropping it.
Rest your arm
Sit upright. Rest the forearm of your catching arm flat on the table, with your hand over the edge.
Do: Forearm flat on the table, hand over the edge.
Why: A supported arm cannot move up or down, so only your fingers do the catching.
Choose the gap between thumb and finger
Hold your thumb and first finger open, 2 cm apart, either side of the ruler. Use the same gap every time.
Do: A 2 cm gap every time.
Why: Your fingers take time to close. The same small gap means the closing time is small and the same each time.
Choose where the ruler starts
Your partner holds the metre rule vertically, 0 cm at the bottom, between your thumb and finger, and lifts it until the 0 cm mark is level with the top of your thumb. Check it before every drop.
Do: Line the zero up with the top of the thumb before every drop.
Why: The reading is how far the ruler fell only if the zero starts level with the top of your thumb.
Choose whether to practise before you start
Use your weaker hand and start recording from your very first catch.
Do: No practice: record every catch from the first one.
Why: You are investigating practice, so the record has to start before any practice (AQA handbook).
Take the readings
10 drops, each read to the nearest 0.5 cm at the top of the thumb and converted to a reaction time.
Repeats: AQA’s handbook records 10 attempts per person. For a factor with two conditions, do at least five drops in each and use the means. A mean reduces the effect of random errors and lets you spot an anomaly; it does not remove a systematic error such as reading the bottom of the thumb.
Make safe and clear upSafety
Stand the metre rule back in the rack (never leave it on the floor). Take off the goggles and return them. Give your results a code instead of a name before you share them with the class. Push the chairs back under the table.
While you take readings
When the ruler is dropped
Your partner waits a different, random time before each drop and gives no warning.
Do: No warning, after a random wait.
Why: If you know when it will drop, you can time your catch instead of reacting to what you see.
Where to read the ruler
Read the mark level with the top of your thumb.
Do: The mark level with the top of the thumb.
Why: The zero started level with the top of your thumb, so the mark there now is how far the ruler fell.
Hazards and control measures
| Hazard | What could happen | Control measure |
|---|---|---|
| A dropped metre rule | Eye injury to the person dropping it if it bounces off the floor | The person dropping wears safety goggles; hold the ruler over the table, not over a gap. |
| Testing people | Discomfort or embarrassment about slow results | Take part only with consent and stop at any time; record results under a code, never rank people by name. |
| A caffeinated drink (caffeine factor only; virtual in this lab) | Raised heart rate, anxiety or poor sleep; a reaction in someone with a heart condition or an allergy | Teacher and parental permission; check medical conditions and allergies first; one can of cola at most; drink it outside the laboratory, never in it. |
| Sitting on a chair at the edge of the table | Falling off the chair while reaching for the ruler | Sit upright and back on the chair; catch with your fingers only, do not lunge for a missed ruler. |
Variables
- Independent: you change
- The factor you chose
- Dependent: you measure
- Reaction time in s
- Control: you keep the same
- Starting position of the ruler. The 0 cm mark level with the top of the thumb every time.
- Gap between thumb and finger. 2 cm every time.
- Arm position. Forearm flat on the table, hand over the edge.
- Same catcher and same dropper. The same pair throughout, so the drops are given the same way.
- No warning. Dropped after a random wait, without a countdown.
- Same hand. The weaker hand throughout, unless the hand is your factor.
- Same conditions for the catcher. Same time of day; no caffeine or energy drinks beforehand; no distractions (unless that is your factor).
- Caffeine: the drink and the wait. The same drink and volume (one 330 cm³ can of cola), and the same 20 minutes between drinking and testing.
Results from a specimen run
| Attempt | Ruler reading in cm | Reaction time in s |
|---|---|---|
| 1 | 23.5 | 0.219 |
| 2 | 21.0 | 0.207 |
| 3 | 20.5 | 0.205 |
| 4 | 19.0 | 0.197 |
| 5 | 21.0 | 0.207 |
| 6 | 20.5 | 0.205 |
| 7 | 20.0 | 0.202 |
| 8 | 0.199 | |
| 9 | 21.5 | 0.209 |
| 10 | 15.5 | 0.178 |
| Attempts | Mean ruler reading in cm | Mean reaction time in ms |
|---|---|---|
| Attempts 1–5 | 21.00 | 207 |
| Attempts 6–10 | 19.40 | 199 |
Anomaly spotted: Attempt 8, retaken.
Processing the data
- Convert a reading to a time
- 0.207 s
- Mean ruler reading
- 19.4 cm
- Mean reaction time (Higher)
- 199 ms
- Show your results
- Line graph: reaction time against attempt number
| Quantity | Specimen run | Accepted |
|---|---|---|
| Mean reaction time for attempts 6–10 (your own reaction time, careful technique) | 199 ms | 197 ms |
Common mistakes and the fix
Mistakes to check in this practical, and what to do instead. In a write-up or an exam answer, the mark goes to naming the step and saying what it does to the readings.
Method: Do without them
Safety only: no effect on the readings, but a ruler that bounces up off the floor could hit the dropper in the eye.
The fix: Put goggles on the person who drops the ruler. A dropped metre rule can bounce off the floor and up into the face of the person dropping it.
Method: Hold your hand up in the air, elbow on the table
Your hand drifts and your arm moves as you catch: the catches scatter about 1.5 times as much and are about 1 cm longer.
The fix: Rest your arm. A supported arm cannot move up or down, so only your fingers do the catching.
Method: Open as wide as is comfortable
Your fingers travel further to close: every catch is about 1–2 cm longer (a systematic error), and the gap varies from drop to drop.
The fix: Choose the gap between thumb and finger. Your fingers take time to close. The same small gap means the closing time is small and the same each time.
Attempt 1: Typed 21.5 cm
The fix: That is the mark level with the bottom of your thumb. Read the mark level with the top of your thumb.
Attempt 1: Typed 23 cm
The fix: Nearly: one 0.5 cm step too low. Check your eye is level with the top of your thumb, then record the half-centimetre mark it is nearest to: it is past half way from 23.0 cm.
Exam answer: Leaving out: Attempt number (the number of attempts / amount of practice)
The fix: Name what you changed: the attempt number (how much practice you had had).
Exam answer: Leaving out: Links the factor to reaction time with a direction (e.g. “reaction time is shorter with …” / “… makes reaction time longer”)
The fix: Name your factor and say how you expect it to change the reaction time: shorter or longer.
Worked exam-style questions
Written for Study Hack in the style of exam questions, on the specimen run above. They are not taken from any exam board's papers. Try each one before you open the worked answer.
- Question 1Independent variable · Applying knowledge[1 mark]
You investigated whether practice changes reaction time. You did ten ruler drops in a row with your weaker hand.
What was the independent variable in your investigation?
Worked answer and how the marks are given
A full-mark answer
The attempt number (how many attempts you had had: practice).
Mark scheme
- Attempt number (the number of attempts / amount of practice) Do not accept “reaction time”, “distance”.
Where marks are usually lost
- Missing: Attempt number (the number of attempts / amount of practice). Name what you changed: the attempt number (how much practice you had had).
- Question 2Mean without the anomaly · Applying knowledge[2 marks]
Look again at Table 2.
Calculate the mean ruler reading.
Do not use the anomalous result.
Mean = cm
Worked answer and how the marks are given
A full-mark answer
mean = (20.5 + 20.0 + 21.5 + 15.5) ÷ 4
= 77.5 ÷ 4
= 19.38 cmMark scheme
- (20.5 + 20.0 + 21.5 + 15.5) ÷ 4 (the anomaly left out) (method)
- 19.38 (cm) (allow 19.4)
- Allow answers from 19.32 to 19.43 cm (the marker's tolerance; correct rounding of the student's own working is also accepted).
- Allow the unit written as centimetres, centimeters, centimetre, cms.
- A correct answer with no working scores full marks.
Where marks are usually lost
- Answer 16.1 cm (no marks). You included the anomalous reading. Leave drop 8 out and divide by 4: 19.38 cm.
- Answer 20.1 cm (no marks). You added all five readings but divided by 4. Leave the anomaly out of the total too.
- Answer 15.5 cm (gains 1 mark). You left the anomaly out of the total but divided by 5. Divide by the number of readings you added: 4.
- Question 3Planning: coffee and reaction time · Knowledge[6 marks]
A student wants to find out if drinking coffee affects reaction time.
They have: a metre rule, a partner, cups of coffee, a conversion table and a timer.
Plan an investigation to find out whether drinking coffee affects reaction time. Include how you would make your results valid.
Worked answer and how the marks are given
A full-mark answer
1. Use the ruler-drop test: a partner holds a metre rule with the zero level with the top of the catcher’s thumb, the thumb and finger a set gap apart and the forearm resting on the table.
2. The partner drops the ruler without warning, at random times, and the catcher catches it. Record the reading at the top of the thumb.
3. Do this 5 times and calculate the mean distance; convert it to a reaction time with the conversion table.
4. The catcher drinks a fixed volume of the same coffee (for example 200 cm³).
5. Wait the same time after drinking (for example 20 minutes), then repeat the 5 drops and calculate the new mean.
6. Compare the means with and without coffee.
7. Keep the same hand, the same person dropping, the same gap and the same time of day. Test several students of the same age, who have had no other caffeine that day.Mark scheme
Indicative content:
- Ruler-drop test: a partner holds the ruler (zero) level with the top of the thumb, drops it, the catcher catches it between finger and thumb
- Detail: zero at the thumb / no warning / record the distance at the top of the thumb / convert to time
- Repeat (at least 3 times) and calculate a mean
- Test without coffee and after drinking coffee (or different volumes) and compare
- Same volume / concentration / type of coffee
- Same time between drinking and testing
- Other controls: same hand, same dropper, same gap, same arm position, same time of day
- Several people of the same age / sex / with no other caffeine
Levels of response Level Marks What the answer does 3 5–6 A coherent method that would give valid results: all the important steps are there, in a sensible order. 2 3–4 A method that might not give valid results: most of the important steps are there, but some are missing or out of order. 1 1–2 A method that would not give valid results: some relevant steps are given, but they are not linked into a workable method. In Study Hack a six-mark answer is not given an automatic level: you tick the points your answer makes, then choose the level that fits it.
- No relevant content: 0 marks.
Evaluate
| Source of error | Type | Effect | Improvement |
|---|---|---|---|
| Zero not level with the top of the thumb at the start | Systematic | Every reading is out by the same 1–2.5 cm, so every reaction time is too short or too long. | Line the 0 cm mark up with the top of the thumb before every drop. |
| Reading at the bottom of the thumb | Systematic | Every reading is 2.0 cm too small, so every reaction time is too short. | Read the mark level with the top of the thumb. |
| Warning the catcher before the drop | Systematic | The catcher times the catch: every time is too short, and anticipation catches are more likely. | Drop without warning, after a different random wait each time. |
| Thumb and finger opened wide | Systematic | The fingers take longer to close, so every catch is about 1–2 cm too long. | Keep the same 2 cm gap between thumb and finger every time. |
| Arm not supported | Random | The hand moves up and down between and during catches, so the readings scatter more. | Rest the forearm flat on the table with the hand over the edge. |
| Getting quicker with practice during the record | Systematic | The first, unpractised catches are longer. If they all fall in one condition, that condition looks slower than it is. | Alternate the conditions (A B B A …), or have practice catches first when practice is not the factor. |
| Natural variation from one catch to the next | Random | No two catches are the same, so a difference between conditions may be due to chance. | Do more drops in each condition and compare the means with the spread. |
| Only one person tested | Random | One person’s results may not be typical, so the conclusion cannot be applied to everyone. | Test more people (of the same age), then pool the class’s means. |
Repeatable. Your own drops in the same condition, with the same method, give similar readings.
Reproducible. Another pair in your class, or a different method such as a computer reaction test, finds the same difference.
Other exam boards
How this practical lines up with other GCSE boards' required or core practicals. Codes only; check your own specification for the exact activity.
| Board | Practical | Match | What is different |
|---|---|---|---|
| AQA | Required practical 7 | This page | — |
| Edexcel | — | Not on its list | — |
Print it
- Blank write-up: the nine-step lab book with the correct table headings, ready to print for a real lesson.
- Specimen lab book: this page's run written up in full, with its exam answers ticked against the mark scheme.
- Printable method card: the practical on one index card. Practise with the cards in Study Hack.
- Practical workbook: a full simulated data set to process on paper, with exam questions and answers.
- Teacher and technician pack: apparatus lists, technician notes and marking points.