0.3 Examples of types of energy store conversions in systems

Energy can be transferred between energy stores in four principal ways

1. By heating - the transfer of thermal energy from a hotter material/object to a cooler material/object.

You can only have a net heat flower from a higher temperature to a lower temperature region.

 

2. By radiation of a wave - sound wave vibrations transfer energy and electromagnetic radiation.

There seven types of EM radiation including microwaves, infrared and visible light.

Infrared radiation is referred to as thermal radiation - its a means of net transfer of thermal energy from a higher to a lower temperature material.

 

3. Flow of electrically - energy is transferred by electrical charge (electrons) moving around an electrical circuit down a potential difference i.e. moving from a higher to a lower potential energy, releasing energy in the process e.g. in the form of heat or light.

See also Usefulness of electricity and energy transfer for lots of examples starting with electricity

 

4. Mechanically - anything  that is moved by a force acting on it involves a mechanical transfer of energy - anything rotating, pushed, squashed or pulled etc.

 

Reminder of the law of conservation of energy

No matter the nature of an energy store or an energy store transfer, the following law applies ...

Energy can be (i )stored, (ii) changed from one form to another and (iii) dissipated, but the total energy of a closed system is constant and you cannot create or destroy energy

There is no net change in total energy, no matter what energy transfers take place.

Dissipated usually means wasted energy like heat spreading out to increase the thermal energy store of the surroundings.

 

In the 19th century scientist began to realise that mechanical work generated heat, and so concluded that there was a connection between them e.g. heat is generated by friction when a mechanical device does work.

Work done in joules = force in newtons x distance through which force acts,

which means the same amount of work transfers the same amount of energy, but not all usefully.

Electrical heating elements transfer energy from an electrical energy store to the thermal energy store of the material being heated e.g. oil in a heater, water in a kettle.

Moving objects have kinetic energy. If you want to slow a moving object down you must reduce its kinetic energy store e.g. car brakes by operating a force. In doing so work must be done and heat from friction is released to increase the thermal energy store of the surroundings.

Whenever you get an increase in temperature of a system, energy must be transferred from one energy store to another.

 

A system is the physical components involved with the energy transfer conversion. e.g. your hand and winding up a clock, a car engine, your muscles being used to lift a weight, a photocell, an electrical appliance, objects colliding.

A closed system is a collection of objects you treat on their own and energy can be transferred between different energy stores of the system, but not between energy stores outside of the system - in other words no energy leaves or enters the defined closed system.

e.g. a hot drink standing on the table - the system includes the surroundings too, because thermal energy is readily transferred to the surrounding air - its an 'open' system..

However, if the hot drink is in a well insulated thermos flask, then this can be considered a closed system.

 

When a system changes it involves an energy transfer.

Energy might be transferred into or out of a system between the different components of a system or between different types of energy stores.

You can transfer energy mechanically when a force is applied to do work e.g. winding up a clock, dragging a heavy box across the floor.

You can transfer energy electrically when work is done by moving charge e.g. an electrical heater, electric motor.

When you raise the temperature of a material (e.g. from a flame, electrical supply, electromagnetic radiation) you increase the thermal energy store of that material.

When your vocal chords vibrate you are transferring kinetic energy into sound energy