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. Type a value in the box next to a slider and
press Enter.
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).