Energy Notes

Energy Stores

• Energy may be stored as:
  • Kinetic
  • Gravitational potential
  • Chemical
  • Elastic (strain)
  • Nuclear
  • Electrostatic
  • Internal (thermal)

Energy Transfer

• Energy is transferred between stores during events and processes.
• Examples of transfer include:
  • Forces (mechanical work done)
  • Electrical currents (electrical work done)
  • Heating
  • Electromagnetic, sound, and other waves

Principle of Conservation of Energy

• In any process of energy conversion, the total amount of energy before and after the conversion is constant.
• Energy is neither created nor destroyed.

Example of Energy Conservation

• Electrical energy (100 J) is supplied to a filament lamp.
• The lamp converts this into:
  • Waste thermal (heat) energy (85 J)
  • Light energy (15 J)
• The total energy after conversion (85 J + 15 J = 100 J) equals the initial electrical energy.

Kinetic Energy

• Unit: Joule (J)
• Formula: $E_k = {1 {2}} m v^2$
  • $E_k$ is kinetic energy.
  • $m$ is the mass (kg).
  • $v$ is the speed (m/s).

Gravitational Potential Energy

• Unit: Joule (J)
• Formula: $\Delta E_p = mgh$
  • $\Delta E_p$ is change in gravitational potentional energy.
  • $m$ is the mass (kg).
  • $g$ is the gravitational field strength (9.8 N/kg).
  • $h$ is the height (m).

Work

• Work is the means of transferring energy from one source to an object.
• Mechanical or electrical work done is equal to the energy transferred.

Work Formula

• Unit: Joule (J)
• Formula: $\Delta E = Fd$
  • $\Delta E$ is the energy change (J).
  • $F$ is the force (N).
  • $d$ is the distance (m).