Launch practical
About 30 minutes
- Set up the bench with the 8 items of apparatus.
- Take the readings yourself, into the results table you draw first.
- Process your results and plot the graph.
- 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 17 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.
How to read it. Eye level with the pointer. Each small mark is 1 mm (0.1 cm): read where its tip crosses the scale.
What it shows
F = k e
Hooke’s law: up to the limit of proportionality, the extension of a spring is directly proportional to the force on it. The spring constant k is the force needed per metre of extension, so a stiffer spring has a bigger k.
The graph to expect. A straight line through the origin while extension is directly proportional to force. Beyond the limit of proportionality the line curves upwards: each extra newton stretches the spring more.
On the AQA 2027 Physics Equations Sheet. Extension is new length minus original length. E = ½ k e² is on the sheet.
Apparatus
| Item | What it is for | Resolution |
|---|---|---|
| Clamp stand with two bosses and clamps | Holds the spring and the metre rule. | — |
| Spring | The object being stretched. | — |
| Metre rule | Measures the position of the pointer. | 1 mm |
| Pointer (splint or wire) | Marks the bottom of the spring against the scale. | — |
| 100 g mass hanger | Carries the masses; counts as the first 100 g. | — |
| 100 g slotted masses (×7) | Each adds 0.98 N of weight. | — |
| G-clamp or heavy weight | Stops the stand toppling. | — |
| Eye protection | In case the spring snaps or springs off the hook. | — |
Method
In our own words, as the Lab runs it. Your school's method sheet may differ in detail.
Which version are you doing?
Boards set this practical slightly differently. Your course setting picks one; you can change it before you start.
Why: The bench and readings are the same; the exam questions follow your board.
Secure the clamp standSafety
Clamp the base of the stand to the bench with the G-clamp, or put a heavy weight on it.
Why: About 800 g will hang from the clamp arm. A secured stand cannot topple.
Hang the spring
Hang the spring from the clamp so it hangs freely.
Why: The spring must stretch vertically without touching the stand or ruler.
Fix the pointer
Fix the pointer to the bottom of the spring, horizontal and pointing at the scale, as close to the ruler as it can be without touching it.
Why: The pointer marks the same point on the spring every time, close to the scale.
Clamp the metre rule
Clamp the metre rule vertically beside the spring, zero at the top.
Why: A vertical rule measures the stretch directly.
Check the rule is vertical
Stand a set square on the base of the stand against the edge of the rule.
Why: A tilted rule makes every reading slightly too large.
Line up zero with the pointer
Slide the rule in its clamp until the pointer sits exactly on the 0 mark.
Why: Each reading is then the extension itself, with no zero error from a pointer resting between marks.
Put on eye protectionSafety
Wear safety glasses for the whole experiment.
Why: A spring can snap or jump off its hook when loaded.
Take the readings
Read the pointer against the ruler at eye level with no masses on. Add one 100 g mass at a time up to 800 g, waiting for the spring to settle and reading the pointer each time. Extension = each reading − the first reading; force = the weight of the masses.
Repeats: Readings are taken as the masses are added and again as they are removed. A mean of the two reduces the effect of random errors, but cannot remove a systematic error such as parallax or a zero error.
Make safe and clear upSafety
Take the masses off one at a time, keeping feet clear. Unclamp the spring and the metre rule and put them away. Take off eye protection once nothing is hanging.
While you take readings
Read again while unloading
After the last mass, decide whether to remove the masses one at a time and read the pointer each time.
Do: Read again while unloading.
Why: Loading and unloading give two readings at each force, so you can work out a mean; and if the spring returns to its original length it has not passed its elastic limit.
Read at eye level
Choose where to look from when you read the pointer against the rule.
Do: Crouch so your eye is level with the pointer.
Why: Looking from above, the pointer lines up with a mark lower down the scale (parallax), so readings come out too large.
Wait for the spring to stop bouncing
After adding each mass, decide when to read: wait until the pointer is still, or read straight away.
Do: Wait until the pointer is still.
Why: A bouncing pointer is between positions; a reading taken too soon is wrong by part of the bounce.
Hazards and control measures
| Hazard | What could happen | Control measure |
|---|---|---|
| Clamp stand toppling with masses hanging from it | Injury to hands or feet | Clamp the base to the bench with a G-clamp or weight it with a heavy mass; do not overhang the bench edge. |
| Masses falling from the hanger | Bruised or broken toes | Add masses gently, keep feet clear of the area under the masses (put a tray or soft landing underneath) and stand rather than sit. |
| Spring snapping or flying off the hook when overstretched | Eye injury | Wear eye protection; do not load the spring beyond the masses provided. |
Variables
- Independent: you change
- Force (weight) on the spring in N
- Dependent: you measure
- Extension of the spring in cm
- Control: you keep the same
- The spring. Use the same spring for every reading.
- Point on the spring that is measured. Always read the same pointer, fixed to the bottom of the spring.
Results from a specimen run
| Force in N | Pointer reading when loading in cm | Pointer reading when unloading in cm | Mean pointer reading in cm | Extension in cm |
|---|---|---|---|---|
| 0.00 | 0.0 | 0.0 | 0.00 | 0.00 |
| 0.98 | 3.7 | 3.8 | 3.75 | 3.75 |
| 1.96 | 7.6 | 7.5 | 7.55 | 7.55 |
| 2.94 | 11.3 | 11.4 | 11.35 | 11.35 |
| 3.92 | 15.1 | 15.1 | 15.10 | 15.10 |
| 4.90 | 19.0 | 18.9 | 18.95 | 18.95 |
| 5.88 | 22.7 | 22.7 | 22.70 | 22.70 |
| 6.86 | 26.5 | 26.5 | 26.50 | 26.50 |
| 7.84 | 30.3 | — | 30.30 | 30.30 |
- Used for the line
- Past the straight part, or left out
Processing the data
- Extension
- 19.0 cm
- Shape of the graph
- A straight line through the origin for every load: extension is directly proportional to force.
- Gradient (extension per newton)
- 3.87 cm/N
- Limit of proportionality
- Every load: it never reached its limit of proportionality
- Spring constant
- 25.9 N/m
| Quantity | Specimen run | Accepted |
|---|---|---|
| Spring constant (the spring’s true value) | 25.9 N/m | 25.9 N/m |
Across 120 simulated careful groups, spring constant (k) came out between 23.5 and 26.4 N/m (median 24.7). That is the simulation's model, not a promise of what a real class gets.
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: Leave it as it is
No effect on your data, but the stand could topple: flagged in the safety review.
The fix: Secure the clamp stand. About 800 g will hang from the clamp arm. A secured stand cannot topple.
Method: Leave the rule where it is
The unloaded pointer sits between marks. You subtract that first reading from every other one, so any error in it shifts every extension by the same amount (a zero error).
The fix: Line up zero with the pointer. Each reading is then the extension itself, with no zero error from a pointer resting between marks.
Method: Skip
No effect on your data, but your eyes are unprotected: flagged in the safety review.
The fix: Put on eye protection. A spring can snap or jump off its hook when loaded.
Pointer reading with no masses: Typed 1 cm
The fix: You are 1 cm out. Find the numbered centimetre line just above the pointer, then count the millimetre marks down from it.
Pointer reading with no masses: Typed 0.5 cm
The fix: Count the small marks again: the longer mark halfway between two numbers is 5 mm (0.5 cm).
Exam answer: Leaving out: The same point on the spring is measured every time (a fixed reference point)
The fix: The pointer marks the same point on the spring for every reading.
Exam answer: Leaving out: The pointer can be close to (touching) the scale, so parallax is reduced
The fix: A pointer can reach right across to the scale, which reduces parallax error.
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 1Variables · Knowledge[2 marks]
You investigated how the extension of a spring depends on the force applied to it.
The spring hung from a clamp stand with a pointer fixed to its bottom end. You added 100 g masses one at a time and read the position of the pointer on a vertical metre rule.
Give two control variables in this investigation.
Worked answer and how the marks are given
A full-mark answer
The original length of the spring.
The diameter of the spring.Mark scheme
Any 2 from:
- The (original) length of the spring
- The diameter of the spring (or thickness of its wire)
- The material the spring is made from
- The spring itself / its spring constant (use the same spring)
- The number of coils (turns) on the spring
- Question 2Spring constant · Applying knowledge[4 marks]
You plotted extension in cm on the y-axis against force in N on the x-axis.
On the straight part of your graph, one of your readings was a force of 7.84 N with an extension of 30.3 cm.
Calculate the spring constant of the spring.
Give the unit.
Spring constant =
Worked answer and how the marks are given
A full-mark answer
e = 30.3 cm = 0.303 m
7.84 = k × 0.303
k = 7.84 ÷ 0.303
k = 25.9 N/mMark scheme
- Extension in metres: 30.3 cm = 0.303 m (method)
- Substitution: 7.84 = k × 0.303, or k = 7.84 ÷ 0.303 (method)
- k = 25.9
- Unit: N/m (unit)
- Allow answers from 25.36 to 26.39 N/m (the marker's tolerance; correct rounding of the student's own working is also accepted).
- Allow the unit written as n/m, nm-1, n m-1, newtons per metre, newton per metre.
- The student must write the unit for the unit mark.
- A correct answer with no working scores full marks.
Where marks are usually lost
- Answer 0.259 N/m (gains 2 marks). You used the extension in centimetres, so you keep the marks for your method but not for converting. In F = k e the extension must be in metres: 30.3 cm = 0.303 m, so your answer is 100 times too small. k = 7.84 ÷ 0.303 = 25.9 N/m.
- Answer 0.0386 N/m (gains 1 mark). You converted the extension correctly but divided the wrong way round. k = F ÷ e = 7.84 ÷ 0.303 = 25.9 N/m.
- Missing: Extension in metres: 30.3 cm = 0.303 m. F = k e needs the extension in metres: 30.3 cm ÷ 100 = 0.303 m.
- Question 3Describing the method · Knowledge[6 marks]
Apparatus: clamp stand, boss and clamp, spring, metre rule, pointer, 100 g mass hanger and 100 g slotted masses.
Describe a method a student could use to investigate how the extension of a spring depends on the force applied to it.
Worked answer and how the marks are given
A full-mark answer
1. Clamp the stand to the bench and hang the spring from the clamp.
2. Clamp a metre rule vertically next to the spring and fix a pointer to the bottom of the spring.
3. With no masses on the spring, read the position of the pointer at eye level. This is the original length.
4. Hang a 100 g mass (0.98 N) on the spring and wait until the spring stops moving.
5. Read the new position of the pointer at eye level.
6. Calculate the extension: extension = new length − original length.
7. Repeat, adding one 100 g mass at a time, up to 800 g.
8. Plot a graph of extension (y-axis) against force (x-axis). The straight part shows extension is directly proportional to force; the spring constant is 1 ÷ its gradient.
9. Wear eye protection in case the spring snaps.Mark scheme
Indicative content:
- Hang the spring from a clamp on a clamp stand
- Fix a metre rule vertically beside the spring
- Measure the original (unstretched) length: the position of the pointer (the bottom of the spring) with no masses
- Use a pointer on the bottom of the spring as the reference point
- Add masses (weights) to the spring
- Add them one at a time in equal steps (e.g. 100 g, about 1 N)
- Measure the new length (position of the pointer) after each mass
- Extension = new length − original length
- Repeat for a range of masses (e.g. up to 800 g)
- Read the scale at eye level, and wait for the spring to stop moving
- Plot a graph of extension against force (straight line through the origin; spring constant = 1 ÷ gradient)
- Safety: eye protection, secure the stand, keep feet clear of falling masses
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 |
|---|---|---|---|
| Parallax when reading the pointer | Systematic | Reading from above or below eye level shifts every reading the same way, so k comes out wrong. | Read with your eye level with the pointer, using a set square to line it up. |
| Reading before the spring stops bouncing | Random | Scatters the points either side of the line. | Wait for the pointer to stop moving before each reading. |
| Zero error in the unloaded reading | Systematic | Shifts every extension by the same amount, so the line misses the origin; the gradient (k) is unchanged. | Line the zero of the rule up with the unloaded pointer, or subtract the unloaded reading every time. |
| Slotted masses not exactly 100 g | Random | A small error, about ±1.5 %, in each force. | Check each mass on a balance and use the measured value. |
Repeatable. Repeat the readings while unloading the spring: if the loading and unloading extensions agree to within the precision of the rule, the results are repeatable.
Reproducible. If another student, or a different group using the same type of spring, finds the same spring constant, the results are reproducible.
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 6 | This page | — |
| Edexcel | 15.6 | Similar, with differences | Also asks for work done, the area under the force-extension graph or ½kx². |
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.