Conservation of Energy – Pendulum Simulation
Conservation of Energy Simulation — Description & Class Activity
What the Simulation Shows
This interactive simulation demonstrates one of the most fundamental laws of physics: energy is never created or destroyed, only transferred between forms.
A ball rolls in a cosine-shaped bowl track. Students drag it to any height to set its starting gravitational potential energy (PE = mgh), then release it and watch the energy continuously transform as it swings.
Two modes:
No Friction — A perfect, idealised system. The ball swings indefinitely. At every point, PE + KE = constant. The Total Energy bar stays completely flat at 100%, proving conservation. This is the theoretical ideal studied in GCSE Physics.
With Friction — A realistic system. As the ball swings, friction converts mechanical energy into thermal energy (heat). The simulation correctly shows that energy still isn’t destroyed — instead E_total = KE + PE + Q remains constant, with the Thermal Energy bar growing as the ball gradually slows and the ball eventually coming to rest at the bottom. This is the real-world scenario.
What students can read in real time:
- Height
hin metres, shown with a dashed line as they drag - Kinetic Energy, Potential Energy, Thermal Energy and Total Energy — all in joules, with colour-coded bars
- A velocity arrow that grows at the bottom (maximum KE) and shrinks at the sides (maximum PE)
- Ball colour shifts from blue (high PE) to orange (high KE) as it moves
Class Activity — GCSE Physics (Energy Transfers)
Learning objectives: Students will be able to describe energy transfer between gravitational PE and KE; explain why the ball slows with friction; and understand that total energy is always conserved.
Duration: 20–30 minutes
Part 1 — Predict before you see (5 min)
Before touching the simulation, ask students to answer in their books:
“A ball is released from a height of 1.2 m on a frictionless track. Where will its kinetic energy be greatest? Where will it be zero? What is its total energy in joules if mass = 1 kg?”
Expected answer: KE greatest at the bottom; zero at the top of each swing; Total E = mgh = 1 × 9.81 × 1.2 = 11.77 J
Part 2 — No Friction investigation (8 min)
Students open the simulation in No Friction mode and:
- Drag the ball to exactly the edge (Max h = 1.5 m). Record Total Energy shown.
- Release. Pause mentally at three points — top of left swing, bottom, top of right swing — and record KE and PE values from the panel.
- Complete the table:
| Position | KE (J) | PE (J) | Total (J) |
|---|---|---|---|
| Left edge (start) | |||
| Bottom of swing | |||
| Right edge |
- Discussion question: “Why does the Total Energy bar never change? What does this tell us about energy?”
Part 3 — With Friction investigation (8 min)
Switch to With Friction mode, drag to the same height and release. Students observe and answer:
- What happens to the height of each swing over time?
- What happens to the Thermal Energy bar as the ball slows?
- Does the Total Energy bar change? Why / why not?
- Where does the “lost” kinetic energy actually go?
Key teaching point to draw out: “Energy hasn’t disappeared — it has transferred to the surroundings as heat. This is why we say energy is always conserved, even though the ball stops.”
Part 4 — Exam-style question (5 min, written)
“A 1 kg ball is released from rest at a height of 1.0 m on a curved track. Using g = 9.81 m/s²: (a) Calculate the ball’s gravitational potential energy at the start. [2 marks] (b) State the ball’s kinetic energy when it reaches the bottom of the track, assuming no friction. [1 mark] (c) In a real track with friction, the ball only reaches 0.8 m on the other side. Calculate the energy transferred to thermal energy. [3 marks]”
Answers:
- (a) PE = 1 × 9.81 × 1.0 = 9.81 J
- (b) KE = 9.81 J (all PE converts to KE)
- (c) PE at 0.8 m = 1 × 9.81 × 0.8 = 7.85 J → Thermal = 9.81 − 7.85 = 1.96 J