Chapter 6. Energy and Its Transformations

Energy is the ability to cause change. Its SI unit is the joule (J) [8][9].

Forms of energy: kinetic, gravitational potential, elastic potential, thermal, chemical, nuclear, electrical and radiant (light).

Key formulas

Kinetic energy: KE = ½mv²

Gravitational potential energy: PE = mgh

Work: W = Fd (force times distance in the direction of force)

Power: P = W/t (SI unit: watt)

Conservation of energy. Energy cannot be created or destroyed, only transformed or transferred. In real systems some energy becomes less useful thermal energy, which is why no machine is 100% efficient [8].

Heat and temperature. Temperature measures the average kinetic energy of particles; heat is energy transferred because of a temperature difference. Transfer occurs by conduction, convection and radiation.

Thermodynamics. The first law is conservation of energy; the second law says that in an isolated system, entropy (disorder) tends not to decrease, so heat flows spontaneously from hot to cold [9].

Energy sources. Fossil fuels, nuclear, solar, wind, hydro, geothermal and biomass. Renewable sources replenish naturally; fossil fuels are finite and release carbon dioxide when burned [13].

Review: What is the kinetic energy of a 2 kg ball moving at 3 m/s? (Answer: ½ × 2 × 9 = 9 J.)