Heat is not a substance
Teaching Guidance
for 11-14
Talking about heating
Wrong Track: When the pan of water is put on the cooker, heat travels through the bottom of the pan and into the water.
Right Lines: When the pan of water is placed on the cooker, heating or warming increases the temperature of the water.
Heat as a state of motion
Thinking about the learning
The underlying problem here is that the wrong track
thinking shown here conjures up an image of heat as being like some kind of substance that passes from the cooker into the water. This is not such an unusual idea. Before 1840 scientists believed exactly the same thing and referred to the heat substance
as caloric.
For example: When a sailor slides down one of the ropes from the top rigging of a sailing ship, his hands are warmed up as he squeezes caloric from the rope.
Nowadays we would simply say that heating is caused by the frictional force between hands and rope.
Of course heat is not a substance, it simply reflects the state of motion of the particles. If some water is heated up, the particles move around more. The image to get over to pupils is one of this heating or warming process.
Thinking about the teaching
Some teachers ban the use of the word heat
in their teaching and insist that pupils refer to the heating or warming process. Following the ideas introduced throughout the previous episodes, we would advise that there is no need to refer to heat at all. Take, as an example, the case of a person warming their hands around a hot mug of soup.
Unhelpful way of thinking: Heat passes from the soup through the mug and into your hands.
Helpful way of thinking: Energy is shifted from the thermal store of the soup to the thermal store of your hands. This happens through the process of conduction which involves the warming by particles pathway.
The word heat
is very commonly used in everyday speech. For example, we might say shut that door and keep the heat in!
In all such cases, you might challenge the pupils to explain what they mean by heat: It's just the state of movement of the particles.
