Energy
Energy is the capacity (or capability) to do work.
Energy is used or consumed when work is done.
The SI unit for energy is joule - J, where
1 J = 1 Nm
which is the same unit as for work.
Imperial Units of Energy
- 1 J = 0.738 ft lb
- 1 ft lb = 1.356 Nm (J)
Energy forms
There can be several forms of energy, including
- mechanical energy
- heat or thermal energy
- electrical energy
- chemical energy
- nuclear energy
- light energy
Energy Efficiency
Energy efficiency is the ratio between useful energy output and input energy, and can be expressed as
μ = Eo / Ei (1)
where
μ = energy efficiency
Eo = useful energy output
Ei = energy input
It is common to state efficiency as a percentage by multiplying (1) with 100.
Example - Energy Efficiency
A lift moves a mass 10 m up by exerting a force of 100 N. The input energy to the lift is 1500 J. The energy efficiency of the lift can be calculated as
μ = 100 (N) 10 (m) / 1500 (J)
= 0.67 or
= 67 %
Related Topics
• Mechanics
Forces, acceleration, displacement, vectors, motion, momentum, energy of objects and more.
• Thermodynamics
Work, heat and energy systems.
Related Documents
1st Law of Thermodynamics
The First Law of Thermodynamics simply states that energy can be neither created nor destroyed (conservation of energy). Thus power generation processes and energy sources actually involve conversion of energy from one form to another, rather than creation of energy from nothing.
Bernoulli Equation
Conservation of energy in a non-viscous, incompressible fluid at steady flow.
Energy and Hydraulic Grade Line
The hydraulic grade line and the energy line are graphical presentations of the Bernoulli equation.
Energy Transfer Equation
Fluid energy transfer.
Flywheels - Kinetic Energy
The kinetic energy stored in flywheels - the moment of inertia.
Food - Energy Content
Energy in carbohydrates, fats and proteins.
Heat, Work and Energy
Heat vs. work vs. energy.
Mechanical Energy Equation vs. Bernoulli Equation
The Mechanical Energy Equation compared to the Extended Bernoulli Equation.
Potential Energy - Hydropower
Elevation and potential energy in hydropower.
Power
Power is the rate at which work is done or energy converted.
Salt Hydrates - Melting points and Latent Melting Energy
Melting points and latent energy of salt hydrates.
Work done by Force
Work done by a force acting on an object.