GRADE 7
Name:
Do you remember what a conductor is? You heard this word when you learnt about
electricity. Conductors allow electricity to pass through them.
Heat conduction is very similar to the conduction of electricity. Materials that
conduct heat allow heat to pass through them.
Heat conduction is a type of energy transfer that
happens between two objects when they are in
direct contact with each other. The heat energy is
transferred from the hot object to the colder object
until their temperatures are the same. Consider
these examples:
Example 1: When you use a stainless steel spoon
to stir hot chocolate before it goes into the
cup, it is cool (room temperature). Once you
have stirred the hot chocolate, the spoon
becomes hot. This means the heat energy
was transferred from the hot water in
the hot chocolate to the cool spoon. This
transfer was from a liquid substance to a solid
substance.
Pots and pans are good
conductors of heat
Example 2: Conduction can happen between
solid substances as well. Think of a pot on a
stove plate. The pot gets hot because the stove plate is hot and is in contact with the
pot. As the stove plate heats up, the heat energy is transferred to the pot base and
eventually to the entire pot.
Materials are either good conductors of heat, or poor
conductors. We need both types because they have different
functions.
Good conductors allow thermal energy to flow through them,
meaning they transfer heat very quickly and easily. Most
metals are good conductors, but some metals like copper
and aluminium are excellent conductors. Pots, frying pans
and baking pans are made of metals because they are good
conductors of heat.
Poor conductors do not transfer heat energy very well. These
are materials like plastic and wood. We call these types of
materials, ‘insulators’. Insulators are very important because
© e-classroom 2014 Wood and
plastic
are poor
conductors
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Grade 7 Term 3 Natural Science: Energy and Change: Heat Transfer: Conduction
Heat transfer: Conduction
Activity 1:
Answer these questions in your class workbook.
1) Write down a definition for heat conduction and give one example.
2) What is a conductor?
3) What is an insulator?
Activity 2: Testing Conduction
Apparatus: A plastic cup, a polystyrene cup, a glass cup,
a steel or aluminium cup, a kettle and water, measuring
jug, drawing pins (x4), Petroleum Jelly, and a stop watch.
Method: Put a some Petroleum Jelly on the bottom of
each cup. Stick a drawing pin into the Petroleum Jelly.
Boil the kettle. Measure and pour 100ml of hot water
into the first cup. Start timing. Stop the stop-watch
when the drawing pin falls off the cup. Repeat exercise
with the other three cups.
cup
Results: Draw a table like this one in your class
workbook and record your observations.
Material cup is
made from
Time drawing
pin took to
fall off
petroleum
jelly
Good or poor
conduction
Answer these questions:
1) Why did we use Petroleum Jelly and a drawing pin in this task? Explain how you know when the heat has been conducted up the sides of the cup.
2) Put the cups in order from the best conductor to the worst conductor.
drawing pin
© e-classroom 2014 stopwatch
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GRADE 7
Grade 7 Term 3 Natural Science: Energy and Change: Heat Transfer: Conduction
they prevent heat loss. Think about pot handles – most are made
from wood or plastic so that you won’t burn your hand when
lifting the pot or the pot lid. Think about a flask – it has a layer
of plastic inside it where you pour the hot drink into. This
insulates the cup preventing that heat from escaping.
GRADE 7
Activity 1:
Answer these questions in your class workbook:
1) Write down a definition for heat conduction and give one example.
Heat conduction is the transfer of heat (or thermal) energy from one substance to another when they are in direct contact with each other.
2) What is a conductor?
A conductor is a substance that allows heat to be transferred through it, quickly and easily.
3) What is an insulator?
An insulator is a substance that does not allow heat to be transferred through it; it prevents heat loss and injury from being burnt.
Activity 2: Testing Conduction
Results:
Material cup is made of Time drawing pin took to Good or poor conduction
fall off
Plastic cup
Times will differ
Poor
Polystyrene cup
Poor
Glass cup
Good
Metal cup
Good
Answer these questions:
1) Why did we use Petroleum Jelly and a drawing pin in this task? Explain how we knew when the heat had been conducted up the sides of the cup.
The Petroleum Jelly secures the drawing pin to the outside of the cup. Heat energy is transferred up the sides of the cup, from the hottest part at the base where the hot water is, to the coolest part at the top. Petroleum Jelly melts when exposed to heat. When it melts, the drawing pin falls off the cup.
We know that the heat has been conducted up the sides of the cup when the Petroleum Jelly melts and the drawing pin falls off.
2) Put the cups in order from the best conductor to the worst conductor.
Metal cup, glass cup, plastic cup, polystyrene cup (Note, the size of the cup and density of the material may vary the results slightly).
© e-classroom 2014 www.e-classroom.co.za
Grade 7 Term 3 Natural Science: Energy and Change: Heat Transfer: Conduction
Answer sheet