Choose an example at the top: 🏀 where does the bounce go? · ⚙️ an electric motor lifting a load · 📊 build a Sankey diagram to
scale · ⛽ how far does a car go on a tank of fuel?
Pick a preset (class demo, slide examples, exit questions) or set the values yourself. Set a value with ▼ ▲ or type it in the box.
Set each value with ▼ and ▲ (hold to go faster; the ↑ ↓ keys or the mouse wheel in the box also work, Shift = ×10), or type a value in the box. ↺ puts it back to its start value. Outside the classroom range the box turns amber ⚠: fine to explore, but the lab can't do this.
Move the pointer over any graph (or tap it): a dashed line shows the values where it cuts each curve, or the values of the nearest data point.
Press ▶ Start (not needed for the Sankey builder). ◂ / ▸ (or the ← → keys) step through the motion and pause.
The middle column shows the free-body diagram and the energy as bars or a Sankey diagram (widths to scale: useful output
straight on, wasted outputs bend away).
Sankey builder: the diagram is drawn on squared paper — count the squares. One output is found by conservation of energy.
● Record saves a trial; the Data tab plots, for example, bounce height after against before (gradient = fraction of energy kept)
or useful energy against input energy (gradient = efficiency).
Work through the Tasks tab. Write explanations on your worksheet.
The physics
efficiency = useful output ÷ total input (energies or powers)
Efficiency is never above 100 % (conservation of energy). The wasted energy is usually thermal energy dissipated to the surroundings.
Sankey diagram rules: input from the left (100 %), arrow widths to scale, input = sum of all outputs, useful output straight on, wasted
outputs bend away, every arrow labelled with name, value and unit.
Bouncing ball: energy kept = mghafter/mghbefore = hafter/hbefore.
Energy density = energy released per kilogram of fuel (MJ kg⁻¹): E = energy density × mass.
Model: g = 9.81 N kg⁻¹; no air resistance on the ball (the energy is lost in the bounce: thermal energy and sound); the contact
time is ignored. The motor lifts its load at a steady speed v = ηPin/W. The car drives at a steady speed: driving force = resistive
forces = Puseful/v. Energy densities from the slide 17 table (uranium: fission).
Newton's laws
The badge above the scene says which law applies at this moment: 1st law — at rest or moving at a constant velocity, the resultant force is zero (ΣF = 0); 2nd law — accelerating, ΣF = ma. The table under the free-body diagram adds up the forces (ΣF) and compares them with m a (▾ folds it). Tick 3rd-law pairs to see every force with its partner: the same size and type, in the opposite direction, acting on the other body (the Earth, the floor, the string, the fluid…).