Energy

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Energy is the capacity or capability to do work and energy is used when work are done.

The unit for energy is joule - J, where

1 J = 1 Nm

which is the same unit as for work.

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 = E_o / E_i         (1)

where

μ = energy efficiency

E_o = useful energy output

E_i = 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 with 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 %

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Related Topics

• Mechanics - Kinematics, forces, vectors, motion, momentum, energy and the dynamics of objects
• Thermodynamics - The effects of work, heat and energy on a system

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 - non-viscous, incompressible fluid in steady flow
• Energy Transfer Equation - Fluid energy transfer
• Energy and Hydraulic Grade Line - The hydraulic grade and the energy line are graphical presentations of the Bernoulli equation
• Equation of Mechanical Energy - The equation of mechanical energy in terms of Energy per Unit Mass, Energy per Unit Volume and Energy per Unit Weight involving head
• Flywheel Kinetic Energy - Kinetic energy and moment of inertia of a flywheel
• Heat, Work and Energy - Tutorial to heat, work and energy - essentials as specific heat and specific heat capacity
• Potential Energy - Elevation and potential energy
• Power - Power is a measure of the rate at which work is done or energy converted
• Work - The amount of work done is the product of the applied force and the distance