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Inside Collection (Course): Natural Sciences Grade 8
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
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
Assignment 1:
Complete:
There are different terms for describing the transfer of heat:
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:
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.
Assignment 2:
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!
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:
2.3 interprets information;
2.4 applies knowledge.
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?
What is absolute zero?
Celsius scale
Kelvin scale:
How is Fahrenheit converted to Celsius?
Converting Celsius to Fahrenheit is done by:
TRANSFER OF HEAT
Activity
Assignment 1:
HEAT AND WATER
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.
Interesting applications of thermal principles result in the following phenomena around us:
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!
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Last edited by Siyavula Uploaders on Mar 9, 2009 2:13 pm -0500.