Bringing together two sets of constraints

Focusing on the learners:

Distinguishing–eliciting–connecting. How to:

• distinguish between things that feel cold and things that are at a low temperature
• separate out the movement of energy from the movement of particles
• draw out pupils' reasoning about temperature and thermal energy

Teacher Tip: These are all related to findings about children's ideas from research. The teaching activities will provide some suggestions. So will colleagues, near and far.

Focusing on the physics:

Representing–noticing–recording. How to:

• separate temperature and thermal energy
• avoid slogans such as heat rises

Teacher Tip: Connecting what is experienced with what is written and drawn is essential to making sense of the connections between the theoretical world of physics and the lived-in world of the children. Don't forget to exemplify this action.

Feeling the effects of temperature and energy

You are watching a bonfire with a hot drink in one hand and a sparkler in the other. Somebody knocks into you. Which will warm your hand more so causing most pain, the spilt drink or the sparks from the sparkler?

The drink would probably be well under one hundred degrees Celsius whilst the sparks from the sparkler, being white hot metal, are several hundred degrees Celsius.

However the relatively small number of particles in the spark means that it has little energy in its thermal store compared to the drink. So, the spark on your hand is hardly felt whilst spilling the drink most definitely is! The drink warms your skin much more (shifting much more energy) and that is what you feel.

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.

Air does the rising

Wrong Track: Switch the gas heater on. Then heat rises out of the top of it.

Right Lines: When the gas heater is switched on, the air above it is warmed up and rises.

Convection

Thinking about the teaching

The idea of heat rising is very common in everyday speech and adds to the notion of heat being some kind of substance. In teaching about convection, it is therefore important to refer explicitly to the air being warmed up, reducing in density and rising through the colder surrounding air. That's why convection currents are a part of floating and sinking in the SPT: Forces topic.

There's a good chance you could improve your teaching if you were to:

Try these

• using the idea of a thermal store as the basis for exploring temperature
• explicitly describing where the energy is before and after a process

Teacher Tip: Work through the Physics Narrative to find these lines of thinking worked out and then look in the Teaching Approaches for some examples of activities.

Avoid these

• heat rises
• conflating power and energy
• mixing up descriptions about processes with those about snapshots, which define the beginning and end of the process

Teacher Tip: These difficulties are distilled from: the research findings; the practice of well-connected teachers with expertise; issues intrinsic to representing the physics well.