Energy & Work (OCR AS Physics): Revision Note

Energy & Work

• Energy is the capacity to do work, therefore:

Transfer of energy = Work Done

• This principle can be used to form mathematic equations for each type of energy

• The type of transfer of energy depends on the scenario

• The most common types of energy that are transformed between each other are:

Kinetic

• Kinetic is the work done by any object which is in motion

E_k = ½ mv²

• Where:

  • m = mass (kg)

  • v = speed of velocity (m s^-1)

Gravitational Potential

• Gravitational potential is the work done against gravity when an object is lifted

E_p = mgΔh

• Where:

  • m = mass (kg)

  • g = acceleration due to gravity (m s^-2)

  • Δh = change in height (m)

Thermal

• Thermal (heat) is the work done on or by a system to transfer heat

E = mcΔT

• Where:

  • m = mass (kg)

  • c = specific heat capacity (J kg^-1 K^-1)

  • ΔT = change in temperature (K or °C)

Elastic Potential

• Elastic potential energy is the work done in stretching or compressing an object

E = ½ Fx = ½kx²

• Where:

  • F = stretching or compressing force (N)

  • x = extension (or compression) (m)

  • k = force constant (N m^-1)

Nuclear

• Nuclear is the work done by nuclei during the processes of fusion and fission

E = Δmc²

• Where:

  • Δm = mass defect (kg)

  • c = speed of light