Starter Physics - Forms of Energy

Forms of Energy

There are many forms of energy. They can be converted from one to another.

starter physics free training course - energy table

Conservation of Energy

Energy can be changed from one form to another, but is never lost.
This means that the total of all energy (in any form) in a system must stay the same.
This is called the law of conservation of energy.
This is very useful if we want to make calculations when the energy changes form.
The SI unit of Energy is Joules (kg.m2/s2).

Motion Energy (Kinetic Energy)

Motion energy (kinetic energy) is the energy required to accelerate an object, or the energy of a moving object.
When we apply a force to an object, the work done (or energy expended) depends on the distance: Energy = Force x Distance = Fs
The energy of a moving object is E = ½ mv2

Potential Energy

Potential energy is stored energy that could be released.
For example: a coiled spring, or a rock held above the ground.
When the rock is released its energy is converted to motion energy, falling to the ground due to gravity.
The potential energy of the rock is E = mgh, and depends on the mass of the rock (m), the acceleration due to gravity (g), and the height above ground (h).

Thermal Energy

A hot object has more energy than a cold one.
Thermal energy is measured in Joules, just like other forms of energy.
The energy required to heat an object depends on the temperature change (ΔT), its mass (m) and the material.
E = mc(ΔT), where c is a constant related to the material.

Electrical Energy

Electrical energy is measured as the amount of charge, q, separated by a potential difference (a voltage, V): E = q.V
This is the potential energy that can be delivered by an electrical circuit.
A more common expression might be E = I.V.t, where I is electrical current, V is voltage and t is time.
So an electrical heater operating at 240 Volts and 10 Amps for 100secs would deliver 240000 Joules of energy (or 240kJoules).

Just remember this next time you boil a kettle.

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