ENERGY

Energy is the capacity of a body to perform transformations and do work.
In prehistoric times, muscular energy was the only source of energy that people had.

- Forms of energy.
· Potential: the height of an object above the ground.
· Kinetic: the energy of physical movement.
· Mechanical: the sum of potential and kinetic energy.
· Sound: the energy of sound waves.
· Electrical: electrical current.
· Nuclear: the energy in the nucleus of an atom.
· Luminous: asociated with lights.
· Thermal: asciated with the movement of particles in matter.
· Chemical: results from the formation or decomposition of substances.
· Electromagnetic: occurs when electrical currents create magnetic fields.

- Units of measurement for energy.
International System: joules (J).
When energy takes the form of heat, we express it as calories (cal).
1 cal = 4.18 J

-Power.
Power (P), expressed in watts, is a measurement of how quickly work is done.
The power of a machine is the amount of work (W), expressed in joules, that it can do in a certain amount of time (t), expressed in seconds (s).
Energy conversion efficiency (%) = output/input · 100