1.9 Heat and temperature

Natural sciences

Grade 8

Energy: electricity, heat and light

Module 10

Heat and temperature

Heat is a type of energy – the energy of the movement of particles. Temperature is the measure of how fast the molecules are moving

How do we measure temperature?

We use a thermometer that consists of a glass tube filled with a liquid such as mercury, which expands when it is warmed.

What is absolute zero ?

The lowest temperature possible, at which it becomes impossible for molecules or atoms to move. This occurs at –273,15 ºC or at 0 on the Kelvin scale. This low temperature was measured in a Finnish laboratory.

Find out what the Kelvin scale is.

You probably know that temperature can be measured on a Celsius scale or on a Fahrenheit scale. Temperatures used to be measured in Fahrenheit, so you may still find appliances that are marked in Fahrenheit, but most appliances nowadays use the Celsius scale.

How do you convert Fahrenheit to Celsius?

Subtract 32 and then divide by 9 and multiply by 5

F to C therefore is (-32 ÷ 9 x 5)

For Celsius to Fahrenheit it is:

÷ 5 x 9 + 32

Activity:

To understand temperature conversions [lo 2.4]

Assignment 1:

Do you know the following?

1. The highest temperature ever recorded on earth is 720 million ºF. It was recorded during nuclear fusion, in the USA.

What would this be in ºC?

2. The highest air temperature has been measured in Libya, at 58 ºC.

What is this in ºF?

3. The lowest air temperature was recorded in Antarctica when the thernometer registered –190 ºF.

What is this in ºC?

Try: www.convert-me.com

Assessment of Temperature Conversions

Were you able to do the conversions?

[LO 2.4]

Heat Transfer

Activity:

To determine terms and concepts involved with the transfer of heat [lo 2.1, lo 2.3, lo 2.4]

Assignment 1:

Complete:

There are different terms for describing the transfer of heat:

• CONVECTION

• CONDUCTION

• RADIATION

Assessment of Terms

Were you able to identify the terms?

[LO 2.4]

Heat and Water

Water has a remarkable capacity for retaining heat.

Much energy is needed for the temperature of water to increase or decrease by 1 ºC.

Various factors influence heat retention by water:

• Water is a liquid.
• Water is transparent and light beams can penetrate to a depth of 20 m.
• A mass of water has waves and currents and vertical movement that can distribute heat.

If you compare the heat retention capacity of the land and the oceans, you will realise that there is a considerable difference.

Capacity for heat

We know that heat causes changes in temperature and that a unit of heat is measured in Joule as it is a type of energy.

Specific heat capacity is the amount of heat that is transferred (required or released) when the temperature of a substance changes by 1 ºC or 1 K.

Water is the most expensive substance to heat because great amounts of heat are required to raise the temperature of water by a few degrees. Water, on the other hand, also provides large amounts of heat when it cools down.

The effect of this is most marked in the oceans, as they are large masses of water. They are warmed very slowly, but also retain the heat for a long time.