P1aL6 Energy and Heat

Key Words

Chemical energy - energy available from chemical reactions.

Concentrated - lots of energy in one place.

Energy transfer - moving energy from one place to another.

Heat energy - energy flowing from a hot object to a cold object.

Kinetic Energy - energy in moving particles or objects.

Particle model - explaining how heat moves in terms of movement of atoms and molecules.

Store of energy - how energy can be kept until it's needed.

Transformation - energy turned from one form to another.

Vibrate - atoms wiggling about, up and down and forwards and backwards.

Grade E

When energy is transferred or transformed, some is wasted.  When you run, energy is turned from chemical (in the food) to movement and a lot of heat.  The body gets rid of the heat by sweating. 

That heat ends up heating the surroundings.

If you shine a powerful torch, that light energy is wasted by heating up the surroundings too.

Grade C

When things get heated up the particles vibrate more.  We can use the particle model to explain how the vibrations are passed on to the surroundings.  For example, in the case of our runner's hot sweaty body, water molecules gain energy, vibrate more, and escape by evaporation.  On a cold day, they condense again rapidly having given up their energy to the surroundings.  You can see the steam coming off the runner.

In sources of energy, the stored energy is concentrated form.  Petrol has a lot of energy for every litre, enough to drive a car for 20 km.

When the energy is spread out, it is much less useful.  A bath full of cold water has much more energy than a saucepan of boiling water, but the energy is not concentrated enough to set off the chemical reactions needed in cooking.

Grade A

A refrigerator is used to concentrating the energy spread out in the contents to cooling fins at the back.  As the energy leaves the food, the food gets cold.  The heat goes to the fins, where it passes to the room by convection.  The fridge is a heat-pump.  Energy is needed to pass from cold to hot.  If the fridge stops, energy flows from the warm room to the cold inside.