Energy Stores and Systems

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Energy is Transferred Between Energy Stores.

Energy gets transferred between objects and when the energy is transferred it is stored in one of the objects energy stores.

There are 8 energy stores.

Thermal (heat) energy stores

Kinetic (movement) energy stores

Gravitational Potential energy stores

Elastic Potential energy stores

Chemical energy stores

Magnetic energy stores

Electrostatic energy stores

Nuclear energy stores

There are four ways that energy is transferred.

Mechanically (by a force doing work)

Electrically (by moving charges)

Heating

Radiation (light or sound)

When a System Changes, Energy is Transferred.

A system is just a fancy word for an object (e.g. air in a piston) or a group of objects (e.g. 2 colliding vehicles) that you are interested in.

When a system changes, energy is transferred. It can be transferred into or away from the system, between different objects in the system or between different types of energy stores.

Closed systems are a system where matter nor energy can enter or leave. The net change in the total energy of a system is always zero.

Energy can be Transferred by Heating...

Take the example of boiling water in a kettle. The water is the system. Energy is transferred to the water from the kettles heating element by heating, into the waters thermal energy store causing the temperature to rise.

You could also think of the kettles heating element and the water together as a two object system. Energy is transferred electrically to the thermal energy store of the kettles heating element which then transfers energy by heating to the waters thermal energy store.

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It can also be Transferred by doing work...

Work done is just another way of saying energy transferred they are the same thing

Work can be done when current flows (work is one against resistance in a circuit) or by a force moving an object

The initial force exerted by a person to throw a ball up does work. It causes an energy transfer from the chemical energy store of the persons arm to the kinetic energy store of the ball and arm.

A ball dropped from a height is accelerated by gravity. The gravitational force does work. It causes energy to be transferred from the balls ravitational potential energy store to its kinetic energy store.