Energy Transfers

• • Everything we do involves a transfer of energy.

There are seven stores of energy:

1. THERMAL– all objects have energy in their thermal energy store. The hotter an object is, the higher its temperature and consequently a higher thermal energy store.

2. MAGNETIC– magnets that attract or repel store each other have energy in their magnetic energy store. (Remember: magnets which attract come together whereas repelling magnets do not touch each other unless forced).

3. CHEMICAL– this is energy that can be released by chemical reactions occurring. Examples: food, batteries and fuels.

4. ELECTROSTATIC– two electric charges which attract or repel each other have energy in their electrostatic energy stores. (like magnetic energy stores but with charges instead).

5. GRAVITATIONAL POTENTIAL– anything that can fall (is high up) is in a gravitational field. It has energy in its gravitational potential energy store. The higher it is, the more stored energy it has.

6. KINETIC– kinetic means moving. Anything which moves has energy in its kinetic energy store.

7. ELASTIC POTENTIAL– anything that can be stretched (elastic bands, springs) has energy in its elastic energy store.

• • Between energy stores, energy can be transferred.
  • When something happens to an object the store of energy in the object you are transferring to increases and decreases in the object you are transferring energy from.

Examples:

1. Dropping a ball. It moves through a gravitational field so energy transfers FROM its gravitational energy store TO its kinetic energy store.

2. Burning a fuel. Energy transferred FROM its chemical energy store TO thermal energy of surroundings.

3. Switching on a basic electric circuit (battery, motor, switch). Energy transferred FROM chemical energy store in battery TO kinetic energy store in the motor. As the motor turns the parts rub together which generates heat. So, energy transfer FROM kinetic energy TO thermal energy store.

4. Stretched spring. When the spring is released, the stored elastic energy transfers TO kinetic energy store.

5. Food. Has energy stored in chemical energy stores. As food goes through your body, it is changed during chemical processes in the body (metabolised). This transfers energy to the body for useful things such as walking and maintaining body temperature.

4 main ways of transferring energy:

1. Mechanically– applying a force to make an object move.

2. Heating – energy transferred from hotter object to cooler objects.

3. Electrically– electric charges moving around a circuit due to a potential difference.

4. Light and sound– light and sound waves carrying energy from one place to another.

• When a force moves an object, energy is transferred. If a force moves an object a distance, energy is transferred. The force need a supply of energy. Then, energy transferred by moving the object (kinetic energy stores).
• To work out how much energy has been transferred:

Energy transferred (in Joules, J) = Force (in Newtons, N) X Distance (in Metres, m)