1.9 Heat and temperature

Assignment 2:

1. Explain why coastal towns have a moderate temperature in comparison with inland towns.

2. When does tea cool down faster? When you add cold milk and then leave it to cool or when you leave it to cool before adding cold milk? Explain.

3. Why does the water at the beach feel pleasantly warm when a cool day follows after several warm days?

4. Which factors play a part in the building up of heat capacity in water?

Assessment Explanations offered for Phenomena

Were you able to identify the symbols correctly? [LO 2.1; LO 2.3; LO 2.4]

Interesting applications of thermal principles have interesting results in the world around us.

Assignment 3:

Discuss each of the following:

Insulation of homes against heat.

Solar ovens.

Why the disk of a plough cooks food quickly.

Make your own solar cooking dish by shaping a sheet of cardboard to look like the disk of a plough and covering it with foil.

Position it at an angle that will ensure maximum sunlight, spear a sausage with a stick and hold it in position to see whether you can cook it with the use of solar power only!

Assessment

LO 2: Constructing Science Knowledge:

The learner will know and be able to interpret and apply scientific, technological and environmental knowledge.

This is evident when the learner:

• recalls meaningful information;

2.3 interprets information;

2.4 applies knowledge.

Memorandum

Activity1

Assignment 1:

HEAT AND TEMPERATURE

Heat is a type of energy – the energy of the movement of particles.

Temperature is the measure of how fast molecules move.

How is temperature measured?

• A thermometer is used. It is a glass tube that contains a fluid, e.g. 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 was measured in a Finnish laboratory.
• You probably know that temperature can be measured on a Celsius scale or on a Fahrenheit scale.
• Some appliances measure in Fahrenheit, while others measure in Celsius.

Celsius scale

• ON this scale, the lowest established point is freezing point, at 0 ºC
• The highest established point is that of boiling water, i.e. steam, at 100 ºC

Kelvin scale:

• For the Kelvin scale, zero is at absolute zero.
• 0 K = -273ºC
• Add 273 to change from Kelvin to Celsius,
• Boiling water 100 ºC is 373 K

How is Fahrenheit converted to Celsius?

• Subtract 32+, divide by 9 and multiply by 5
• F to C therefore is (-32÷9x5)

Converting Celsius to Fahrenheit is done by:

• F = C ÷ 5 x 9 + 32

TRANSFER OF HEAT

Activity

Assignment 1:

• CONVECTION: Movement of heat through air, e.g. air currents, e.g. fan heaters, warm winds.
• CONDUCTION: Distribution of heat through solid objects, e.g. warm rocks.
• RADIATION: Distribution of heat from heat-producing objects, e.g. the sun, a heater.

HEAT AND WATER

• Water has exceptional heat retention qualities.
• Much energy is required for the temperature of a mass of water to be increased or decreased by 1 ºC.
• The relevant factors involve the following:
• Water is a liquid;
• Water is transparent and light beams can penetrate up to 20 m into water;
• Any mass of water has waves and currents and vertical motion that can distribute heat.
• If you compare the heat retention capacity of the land and the ocean, you will realise that there is a considerable difference.

THERMAL CAPACITY (HEAT CAPACITY)

Assignment 2:

We have mentioned that heat causes a change in the temperature and that the unit for measuring this heat is Joule, because it is a type of energy that is involved.

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

• Water is the most expensive substance to heat because large amounts of heat are required to increase the temperature by a few degrees only.
• Water, on the other hand, yields large amounts of heat when it is cooled down.
• The effect of this is most evident over the oceans, which are large water masses.
• Water is heated very slowly, but retains heat for a long time.

Interesting applications of thermal principles result in the following phenomena around us:

• Discuss the following:
• Insulating houses against heat: houses lose 25 % of their heat through roofs and 25 % through the floor
• Solar ovens: a polystyrene cooker lined with foil provides a wonderful alternative for areas where there is no electricity
• Why the disk of a plough cooks food quickly

For the Learner

Make your own solar cooking dish by shaping a sheet of cardboard to look like the disk of a plough and covering it with foil.

Position it at an angle that will ensure maximum sunlight, spear a sausage with a stick and hold it in position to see whether you can warm it with the use of solar power only!