Energy, Work and Power: notes

Energy

• Conservation of energy: energy is never created or destroyed. It changes form.
• Kinetic energy: KE = ½mv². A 2 kg ball at 3 m/s has 9 J.
• Gravitational potential energy: PE = mgh. A 2 kg mass raised 5 m gains 100 J (g = 10 N/kg).
• Efficiency: useful energy out divided by total energy in, x 100%. 60 J useful from 200 J in is 30%.

Work and power

• Work done: force x distance moved in the direction of the force. 40 N over 3 m is 120 J.
• Power: work done divided by time. 120 J in 4 s is 30 W.

Energy sources

• Renewable: solar, wind, hydroelectric, geothermal. They are not used up.
• Non-renewable: coal, oil, gas, nuclear fuel. They run out.
• Fossil fuels: burning them releases carbon dioxide, which adds to global warming.