Falling with air resistance: paper cake cases, a model parachute and the skydiver sim
Drop stacks of nested paper cake cases from 2.5 m and find their terminal velocity with a stopwatch or a motion sensor's distance–time trace, plot v² against the number of cases, time a model parachute with different canopies and loads, then predict and watch a skydiver's forces and speed–time graph as he falls, opens his canopy and lands.
Dynamics · covers the O-Level, IGCSE, GCSE topic
What the sim shows
Model: weight W = m g (g = 10 N/kg) down, air resistance D = k v² up (beyond the syllabus; k = ½ ρ C A, ρ = 1.2 kg/m³). The resultant W − D speeds the object up until D = W: terminal velocity v = √(m g ÷ k), so for one shape v² ∝ m. Cake cases 0.40 g each, drag factor chosen for a typical terminal velocity; dropped from 2.500 m, timed over the last 1.000 m by a stopwatch with a reaction-time spread, or by a motion sensor. Skydiver 80 kg: 55 m/s, then 5.0 m/s with the canopy (from memory), the canopy opening over 2.5 s. Idealised: one air density at every height, shapes that never change, no swaying.
- The stack of cake cases, or the model parachute: the part to watch
- Board with three metre rules, red tape at 1.000 m, motion sensor, release flaps, tall stand, landing cards, step platform, stool, data logger, stopwatch
Use it in your lessons
- Try it here: anyone can unlock 2 figures free, and a free account unlocks up to 5. Runs on a laptop, a Chromebook or a phone; nothing to install.
- Present it and share student links with the teacher plan, from US$5 a month, billed yearly.
- Put it on your own website or LMS for US$9, paid once, or every sim from US$29 a month.
Free guide: 12 practicals as sims, and how to run one in a lesson →
Need a version for your exact set-up? Have one made: US$49 a figure in an order of 5.
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