Physics · 1.1 Measurement techniques · Paper 6 practical
Simple Pendulum. Time it.
Determine the acceleration of free fall g, or investigate how length l affects period T. Follows the Cambridge IGCSE 0625 ATP procedure — count 20 oscillations, plot T² against l, gradient = 4π²/g.
0625 Topic 1.1 — Measurement techniques
0625 Topic 1.7 — Energy (KE ↔ PE)
Paper 6 — Alternative to Practical
00.00 s
Oscillations 0 / 20
Tip: in setup mode you can drag the bob directly to set the angle. Shortcuts Space release/pause · T start timing · R reset.
Variables — change to reset experiment
60
9.81
100
10
⚠ Angle > 15° — the small-angle approximation T = 2π√(l/g) breaks down.
The measured period will exceed the theoretical period — useful to verify the approximation limit.
Live readouts
Current angle θ
+10.0°
Angular velocity ω
0.00 rad/s
Theoretical T = 2π√(l/g)
1.554 s
Measured T (last trial)
— s
Kinetic energy (KE)
0.00 mJ
Potential energy (PE)
0.00 mJ
KE + PE is conserved — the bob trades them as it swings (Topic 1.7).
Trial data — vary l, measure T
Press Start timing 20 oscillations at three or more different lengths to plot T² vs l.
T² vs l — gradient → g
📋 Method (Cambridge ATP procedure)
- Measure the length l from the bottom of the split cork to the centre of gravity of the bob using a metre rule (resolution ± 1 mm).
- Displace the pendulum by a small angle (θ < 15°) and release it smoothly to prevent elliptical motion.
- Start the stopwatch as the bob passes the central equilibrium position (the fiducial marker).
- Count 20 complete oscillations (N = 20). One oscillation = a full "forth-and-back" cycle.
- Stop the watch on the 20th count. Record the total time t.
- Calculate the period T = t / 20.
- Repeat for five different lengths, keeping the mass of the bob and the initial release angle constant.
Analytical control: plot T² (y-axis) against l (x-axis). The line is straight through the origin with gradient 4π²/g. Therefore g = 4π² ÷ gradient.
⚠ Sources of error & precautions
- Reaction time when starting and stopping the stopwatch — mitigate by timing 20 oscillations and dividing, not timing one.
- Parallax when reading the metre rule — view the scale perpendicular (90°) to the markings.
- Length measurement — measure to the centre of gravity of the bob, not the top of the string or the side of the bob.
- Air resistance — small effect; use a heavy bob and a small angle to minimise.
- Elliptical swing — release the bob smoothly along the swing plane; do not push sideways.
- Pivot slip — clamp the split cork tightly to the retort stand so it does not move during the swing.
🧪 Apparatus list
- Pendulum bob (heavy metal, e.g. brass)
- Length of inextensible string (~1.2 m)
- Split cork to clamp the string
- Retort stand with boss and clamp
- Metre rule (resolution ± 1 mm)
- Digital stopwatch (resolution ± 0.01 s)
- Fiducial marker (a small card behind the equilibrium position)
🎯 Syllabus reference (Cambridge IGCSE 0625)
- 1.1 Measurement techniques — use a metre rule for length; use a digital stopwatch for time intervals; measure short time intervals using multiple oscillations to reduce the percentage uncertainty due to reaction time.
- 1.7.1 Energy — describe energy being stored as gravitational potential and kinetic; recall that energy is transferred between stores without loss (in the absence of friction).
- Paper 6 — plan an experiment; record results in a table with quantity and unit in the header; plot a graph with sensible scales and a line of best fit; calculate a gradient using a large triangle on the line; draw a conclusion supported by the data.
Ask the lab assistant
Stuck on method, calculation, or sources of error? Ask in plain English — your current variables and last measurement will be attached automatically.