Heat

Thermal ENERGY

What is HEAT?• Form of energy where it flows from one object to another.• Particles move about more and take up more room if heated – this is why things expand if heated.• It is also why substances change from:

solids liquids gases , when heated.

Sources of heat

1) Sun, it is the main source of heat.2) Fire, light bulbs and stoves3) Rubbing two objects together

Transferring

Heat is transferred from a hotter to a colder body. The hot body gets colder and the cold body gets hotter

• Example 1:• When you use a toaster, not only do you heat a bread but you also heat the air

around it. When you touch the warm toast, the thermal energy moves to your hand.

• Example 2:• 1)Fire transfers thermal energy to water and surrounding air.• 2)A hot tea is made.• 3)Some energy is transferred to the cup and the surrounding air.• 4)The tea is drunk.• 5)Some energy is transferred to the human body.

Heat and Temperature

• The temperature of an object tells us how HOT it is.• The greater the thermal energy, the higher the

temperature.• Measured in degrees Celsius - °C• Temperature is the measure of thermal energy.

Heating and Cooling

• If an object has become hotter, it means that it has gained heat energy.

• If an object cools down, it means it has lost energy.

Heating and Cooling cont…

• Heat energy always moves from:

HOT object COOLER object

e.g.Cup of water at 20 °C in a room at 30°C - gains heat energy and heats up – its temperature rises

Cup of water at 20 °C in a room at 10°C loses heat energy and cools down – its temperature will fall.

Measuring temperature

• Temperature is measured using a Thermometer.• It is a device for measuring thermal energy. • A thermometer is made of glass.• At one end there is a bulb which contains a liquid.• The liquid can be mercury or alcohol. When energy is transferred

to a liquid, the particles of the liquid moves faster and farther apart.• This movement makes the liquid expand inside the thermometer.

• Temperature at which the water freezes= 0 ºc• Temperature at which the water boils = 100 ºc• The human body’s temperature = 37 ºc

Calibration system for thermometers are:

• 1) Fahrenheit F• 2) Celsius or centigrade ºc

Thermal Conductors/ Thermal Insulators

• If a substance easily allows heat to move through it, we can say it is a good conductor of heat. e.g.: most metals (steel and aluminium)

• If a substance does not allow heat to pass through it easily, we can say it is an Insulator. E.g.: wood, plastic, glass , rubber ,cotton ,wool and fur.

• Why do many sauce pans have plastic handles?