INVESTIGATING HEAT ENERGY

Heat is a form of energy that is measured in joules(J).

Heat and temperature are not the same.

Temperature is a measure of how hot or cold something is.

It is measured in degrees Celcius (0C) using a thermometer.

7.1 Heat and temperature

For example, each spark in a sparkler is a tiny piece of white hot metal, and its temperature may be as high as 8000C.

Boiling water is only 1000C. However, if a spark falls on your

hand you don’t even feel it. This is because each spark

contains only a small amount of heat energy.

Heat and temperature

When you heat an object, the particles in it move more rapidly and have more energy.

This is why the temperature is higher.

When the particles lose energy and move more slowly, the temperature is lower.

For example, slushies and cups of coffee.

Heat and particle theory

Heat energy can be transferred in three different ways:ConductionConvectionRadiation

7.2 Heat transfer

Conduction – this is how heat energy is transferred through solids.

For example, when a hot metal rod comes in contact with a hot flame, it becomes hot quickly. The heat is transferred along the rod by the process of conduction.

Metals are good conductors Plastics and glass are poor

conductors

Heat transfer (conduction)

Convection – this is how heat energy is transferred in liquids and gases.

For example, convection currents occur when water particles at the bottom of a beaker are heated, The hotter (less dense) water near the bottom rises, and the cooler water becomes more dense and sinks.

Can you think of other types of convection currents?

Heat transfer - Convection

Convection currents in a radiator - warm air rises and cool air sinks

Convection currents in the mantle drive tectonic plate movement

Convection currents in the atmosphere drive weather patterns

Radiation – this is how heat energy is transferred from the sun to the earth.

For example, when the sun heats the earth, heat is transferred by the process of radiation.

Can you think of other situations in which radiation might occur?

Heat transfer - Radiation

Xrays

Mobile phone radiation

Heat radiation

Medical Radiation

Cosmic radiation

Dark coloured surfaces are better absorbers of radiation than light-coloured surfaces.

This is because light-coloured surfaces reflect more radiation.

Absorbing and emitting Radiation

Solar panels have dark shiny surfaces to absorb more radiation.

Roof insulation has light-coloured surfaces to reflect more radiation.

All objects emit infrared radiation if they are at a higher temperature than their surroundings.

Rough surfaces also radiate heat more effectively due to their greater surface area.

Many animals will also sunbath to absorb radiation.

Absorbing and emitting Radiation

An object that is warmer than its surroundings will lose heat until it is the same temperature as its surroundings.

Similarly, an object that is cooler than its surroundings will gain heat from its surroundings.

Insulators are used to control the transfer of heat.

For example, Eskys and flasks

Controlling heat transfer

Turn to page 168 in your text book Complete 2 activities from the following

list:FirewalkingHow does a thermos work?Which is the coolest colour to wear?Does white coffee cool faster than black coffee?Why use a lid?Designing a house

7.3 Heat in everyday life

Energy: Review questions Complete the following questions1. Explain the difference between heat and

temperature. Give the units that each is measured in

2. Why do you not get burned by sparklers, even though they have a higher temperature than boiling water?

3. Give the three different ways in which heat can be transferred. Give an example of each.

4. Why are plastics used to make handles for saucepans, kettles and frying pans?

5. Why is radiation of heat important?6. Can you think of why absorbing panels of solar

water heaters are painted black?7. Name three ways in which insulators are used to

control the transfer of heat.