Q: What does IP Physics Plasticine: 7 Experiments that Turn Soft Clay into Hard-Won Marks cover? A: Malleable, cheap and exam-friendly, plasticine is the stealth MVP of IP and H2 Physics practical work.
TL;DR Plasticine's super-power is that it can be reshaped in seconds, sticks to things on impact and sinks slowly in syrup. Those three traits unlock at least seven physics ideas-from density checks to perfectly inelastic collisions-that frequently appear in IP weighted assessments and H2 practical papers. This article lays out the exact mini-labs, common slip-ups and a 5-day micro-practice plan so you can turn a $2 block of clay into solid grades.
Exam-Scope Disclaimer
Stokes' Law is not listed as required knowledge in the current IP Physics or H2 Physics syllabuses. Examiners may, however, supply unfamiliar relationships (including Stokes'drag) in an open-ended design or data-handling question and ask you to derive or apply them using provided graphs or first-principles ideas. Memorising the Stokes'Law equation is therefore optional - keep sub-section 2.2 as an enrichment task, or skip it entirely if you prefer to focus strictly on examinable content.
1 Why every H2 lab issues a lump of plasticine
Malleable & re-usable - one block can be rolled into spheres, flattened into pucks or packed onto carts in seconds.
Safe & classroom-friendly - no shards, no bounce, no toxic dust.
Density ≈1.4g⋅cm−3
-heavy enough to sink in water yet light enough to reach terminal velocity in a 1 m-tall syrup column.
Sticky on impact - guarantees a perfectly inelastic collision every time, a requirement in many momentum tasks.
IP exam setters exploit those virtues because they let students focus on data handling and uncertainty, not tricky apparatus.
2 Seven physics ideas a clay lump can prove
2.1 Density without Archimedes
Roll five different-mass spheres, measure mass (digital balance) and diameter (vernier calliper). A log-log mass-vs-diameter³ plot gives the density as the gradient. Students spot linearisation and propagate percentage uncertainties in one go.
2.2 Stokes' law in a jam jar
Drop the spheres through glycerine or honey, time the last 10 cm fall. Plot radius² against terminal velocity; gradient yields the fluid viscosity via vt=92η(ρsphere−ρfluid)gr2. A single kitchen jar turns into an H2-level viscometer.
2.3 Perfectly inelastic collisions on a bench-top
Load a rolling dynamics cart with a motion sensor, fire a plasticine bullet from a spring launcher. The bullet sticks; momentum is conserved but kinetic energy drops-students calculate the lost KE and discuss energy pathways.
2.4 Centre of mass & counter-intuitive balance
Shift tiny lumps along a ruler until it balances on a pencil; plot distance-of-lump vs centre-of-mass position to verify the lever rule. A neat visual for stability questions.
2.5 Elastic vs plastic deformation
Clamp a strip of plasticine and hang masses; strain rises but never returns-an instant demo of plastic region beyond Hooke's law. Compare to a steel spring on the same rig.
2.6 Rolling friction & energy dissipation
Roll an iron ball into a plasticine target on a smooth track; measure the embed depth to estimate the work done by rolling friction. AAPT's experiment shows how multiple concepts intertwine.
2.7 Pressure imprint mapping
Press a loaded test-tube onto a plasticine pad; the contact area reveals pressure distribution-great for qualitative questions on pressure = force/area.
3−5 plasticine spheres, radii 3mm−7mm, measured with a vernier calliper.
Electronic balance ±0.01g.
Cooking oil (≈0.065Pas at 25∘C).
Digital thermometer ±0.1∘C clipped midway down the column.
Stopwatch capable of 0.01s or phone camera 120 fps for video timing.
Step-by-step method (justified)
Calibrate & condition: Warm the oil bath to 25±0.5∘C and stir gently to ensure uniform temperature (controls viscosity).
Measure sphere mass & diameter three times each; compute mean radius and density to ±1%.
Release protocol: Hold the sphere with tweezers at centreline to avoid wall effects, then let go without imparting spin.
Timing window: Start timer 5 cm below the oil surface (allows acceleration phase to finish) and stop 25 cm lower. Distance is marked with masking tape for consistency.
Repeat for each radius thrice; discard trials where the sphere touches the wall or creates visible wake (possible Re>1).
Clean-up: Retrieve spheres with perforated spoon; wash glassware with detergent, dry, store. Follow glassware safety to prevent breakage.
Uncertainty & error analysis
Random: reaction-time error (~0.2 s) divides by long timing distance, so percent uncertainty ≈0.2s/4s≅5%. Reduce by video analysis.
Systematic: ignoring buoyancy term overestimates η by ≈10%. Always subtract ρoil from ρsphere.
Wall effect: keep cylinder diameter ≥ 10 x sphere diameter to keep correction <1%.
Temperature drift: viscosity of vegetable oils changes ≈2−3%K−1; record bath temperature every two trials.
Apply propagation of uncertainty formally (GUM) when reporting η.
Typical data & sample calculation
For a 5.00mm radius sphere (mass = 0.52g) falling 0.25m in 3.60s at 25∘C:
Literature viscosity for canola oil at 25∘C≈0.067Pa⋅s - within 4% of accepted value.
Validity checks & improvement ideas
Check linearity: plot v against r2; R2>0.99 confirms Stokes regime.
Lower Re further: use smaller spheres or colder oil if curvature appears.
Automate timing with Light-Gate + Data-logger to cut human reaction error to < 1%.
Compare liquids: run the same spheres in water and glycerine to highlight viscosity contrast and reinforce concept transfer.
4 Common mistakes & lightning fixes
Slip-up
Why it hurts
Fix in 10 s
Forgetting buoyancy term in Stokes analysis
Over-estimates viscosity by \(~10 \%\)
Write \(\rho_\text{sphere}-\rho_\text{fluid}\) first, highlight in colour
Calling collision “elastic” because carts rebound slightly
Loses theory marks
Stick an extra sliver of clay to guarantee zero rebound
Measuring sphere diameter with a ruler
\(\pu{\pm 1 mm}\) error dominates
Use a vernier; take three perpendicular readings
Rounding mid-calculation
Data scatter inflates
Keep one extra s.f. until final line
5 5-Day micro-practice sprint
Day
15-min mission
Concept locked
1
Roll 3 spheres, plot \(\text{mass}\) vs \(\text{diameter}^3\)
Density & linearisation
2
Drop one sphere in honey, record video at \(120\) fps
Terminal velocity
3
Glue clay to air-track glider, do a sticky collision
Momentum conservation
4
Balance a ruler with clay lumps, sketch CoM shift
Centre of gravity
5
Quiz yourself: list every uncertainty source seen
PDO reflex
Tick each box, snap a photo, post to class chat-peer accountability matters.
6 Quick FAQ
Q Why does IP love “plasticine questions”? Because the same blob lets exam writers weave density, kinematics and mechanics into one neat package, mirroring the cross-topic flavour of A-Level practicals.
Q Won't the clay absorb oil and change mass? Mass change over a 30s run is <0.1% - well inside typical measurement uncertainty.
Q Is Blu-Tack a valid substitute? Blu-Tack is visco-elastic; rebound spoils perfectly inelastic assumptions. Stick to plasticine.
