Everything on the GCSE Physics Key Energy Equations poster is written out below, section by section. Use it to search the sheet, copy parts into your own notes, or check a fact quickly.
Kinetic energy (KE)
KE = ½ m v² - kinetic energy (J) = ½ × mass (kg) × speed² (m/s)²
Example: An 800 kg car travels at 10 m/s. KE = ½ × 800 × 10² = 40,000 J (40 kJ).
Gravitational potential energy (GPE)
GPE = m g h - gravitational potential energy (J) = mass (kg) × gravitational field strength (N/kg) × height (m)
On Earth, g = 9.8 N/kg.
Example: A 70 kg climber is 15 m above the ground. GPE = 70 × 9.8 × 15 = 10,290 J (10.3 kJ).
Elastic potential energy (EPE)
EPE = ½ k e² - elastic potential energy (J) = ½ × spring constant (N/m) × extension/compression² (m)²
Example: A spring with k = 100 N/m is stretched by 0.15 m. EPE = ½ × 100 × 0.15² = 1.125 J.
Specific heat capacity
ΔE = m c ΔΘ - energy transferred (J) = mass (kg) × specific heat capacity (J/kg°C) × temperature change (°C)
Example: Heating 0.5 kg of water, where c = 4200 J/kg°C, by 20°C. ΔE = 0.5 × 4200 × 20 = 42,000 J.
Work done
W = F s - work done (J) = force (N) × distance moved in direction of force (m)
1 joule = 1 newton-metre.
Example: A box is pushed with a force of 30 N over a distance of 4 m. Work done = 30 × 4 = 120 J.
Efficiency
Efficiency = useful energy output ÷ total energy input (× 100 for a percentage)
Equivalently: Efficiency = useful power output ÷ total power input (× 100 for a percentage)
Efficiency is always between 0 and 1 (or 0% and 100%).
Example: A machine is given 2000 J of energy; useful output is 600 J. Efficiency = 600 ÷ 2000 = 0.30 (30%).