An interactive learning module covering work done, gravitational potential energy, kinetic energy, conservation of energy, and power — complete with live simulations.
In physics, work is done when a force causes an object to move a distance in the direction of the force. Work done is a measure of energy transfer — whenever work is done on an object, energy is transferred to or from it.
W = F × d
Work Done (J) = Force (N) × Distance (m)
1 Joule = 1 Newton × 1 metre
Example: A box is pushed with a force of 50 N for a distance of 10 m. Calculate the work done.
W = 50 N × 10 m = 500 J
Gravitational Potential Energy is the energy an object possesses because of its position in a gravitational field. The higher an object is lifted and the greater its mass, the more GPE it stores.
GPE = m × g × h
GPE (J) = mass (kg) × g (N/kg) × height (m)
On Earth, g ≈ 9.8 N/kg
Example: A 2 kg book is lifted to a shelf 1.5 m high (g = 9.8 N/kg).
GPE = 2 × 9.8 × 1.5 = 29.4 J
Kinetic Energy is the energy an object possesses due to its motion. It depends on the mass of the object and the square of its velocity — doubling the speed quadruples the kinetic energy.
KE = ½ × m × v²
KE (J) = 0.5 × mass (kg) × velocity² (m/s)²
Example: A 1000 kg car travels at 20 m/s. Calculate its KE.
KE = 0.5 × 1000 × 20² = 0.5 × 1000 × 400 = 200,000 J (200 kJ)
The principle of conservation of energy states that energy cannot be created or destroyed — it can only be transferred from one store to another or dissipated. When an object falls, GPE converts to KE; when work is done against friction, energy is transferred to thermal energy stores.
Example: A 0.5 kg ball is dropped from 10 m.
Initial GPE = 0.5 × 9.8 × 10 = 49 J
At the bottom (no air resistance): all GPE → KE = 49 J
49 = ½ × 0.5 × v² ⇒ v² = 196 ⇒ v = 14 m/s
Watch GPE and KE swap back and forth while total energy stays constant. Click and drag the bob to set its starting position, then release to swing!
Power is the rate at which work is done or energy is transferred. A more powerful machine can do the same amount of work in less time.
P = W / t or P = E / t
Power (W) = Work Done (J) / Time (s)
1 Watt = 1 Joule per second
Example: A crane lifts a 500 N load through 10 m in 20 s.
Work Done = 500 × 10 = 5000 J
Power = 5000 / 20 = 250 W
Two cranes lift the same load the same height — but Crane B has twice the power. Watch the difference!
1. If a force of 25 N moves an object 4 m, how much work is done?
2. A 5 kg object is lifted 2 m. What is its GPE? (g = 9.8 N/kg)
3. A 2 kg ball moves at 3 m/s. What is its KE?
4. Power is defined as:
5. If 600 J of work is done in 30 seconds, what is the power?
6. A 4 kg object falls from 5 m. What is its speed just before hitting the ground? (g = 9.8 m/s², no air resistance)
7. If a car doubles its speed, its kinetic energy:
8. Machine A (200 W) and Machine B (400 W) both do 4000 J of work. How long does each take?