These are some common misunderstandings about fire. They acknowledge that children have made reasonable sense of the ideas based on their experience and should be validated as such. Keep them in mind while teaching – and address them as they come up.
Materials like wood or paper disappear
In combustion, students frequently believe materials like wood or paper are just used up and disappear. In their view, air (oxygen in the air) has little to do with burning. In fact, the wood or paper react with oxygen to form compounds such as water and carbon dioxide, but these compounds are colourless gases so cannot be seen. The energy and mass from the original materials are conserved – they’ve changed, not disappeared.
Charcoal (carbon) appears from the burning rather than the material
In burning carbon-based materials such as wood, students believe that charcoal (carbon) appears from the burning rather than the material. After the fire has been burning for a while, most of the hydrocarbons have been released (burned) so that all that is left is charcoal, which is almost pure carbon with some minerals.
Fire is alive
Students often view fire as alive rather than the visible evidence of an energy change in a chemical reaction. We support this by using words like “feeding the fire’” “watch it die”, “watch it grow”. One way of remembering the scientific definition of living things is to remember MRS C GREN. The letters stand for things that are relevant to living things – Movement, Respiration, Sensitivity, Circulation, Growth, Reproduction, Excretion, Nutrition. (Fire fits all parts of this description except fire does not have a circulation system – moving substances to and from cells.)
Chemical change is something being added
Students often see chemical changes as something being added (for example, carbon dioxide and water being added in the process) rather than the chemical change being interactive (for example, volatile gases interacting with oxygen to produce different products – not added products – such as carbon dioxide and water).
Heat is a substance or a measure of hotness
Students often see heat as a substance or as a measure of hotness, rather than the flow of energy from a warm object to a cooler one.
- Heat could be perceived as a substance because students believe something has been added to a material.
- Heat is perceived as a measure of hotness because we often use heat as an everyday word to mean something warm or hot – “This has a great deal of heat in it.”
Heat is not energy
Students will often not regard heat as energy. They perceive heat more as a measure of hotness or a substance (see above), rather than the result of the movement of tiny particles called atoms, molecules or ions in solids, liquids and gases.
Heat only travels upwards
Students often say that heat only travels upwards. This is probably because they often hear the phrase “heat rises”. It does go up through convection currents, but can travel anywhere through conduction and radiation as well. See Heat energy.
Heat and temperature mean the same thing
To students, heat and temperature often mean the same thing.
- Heat is the transfer of energy between two objects or substances of different temperatures (the flow going from the hotter object to the cooler one).
- Temperature is the measure of particle movement or kinetic energy of the object, which determines the degree of how hot or cold an object is.
Temperatures of objects depend on their size
Students often think temperatures of objects depend on their size. Temperature does not depend on the amount of material there is. Both a very small and very large object could be the same temperature (have similar particle movement in them), but the large object would have much more heat energy than the small object. This is because the large object has a lot more matter and therefore has a lot more tiny particles moving or vibrating than the smaller object.
Smoke is part of the wood released when the wood burns
Students often think smoke is part of the wood that is somehow released when the wood burns, rather than unburnt particles of carbon and gases produced by the burning process.
Smoke is harmless
Some students have the concept that smoke is harmless. It’s actually very dangerous – 75% of people who die in fires die from the smoke, not the flames. This is due both to the toxic gases and particles in smoke that are inhaled and to the invisibility of smoke that stops people from seeing their way out of a fire.
Furniture will protect you from a fire
Children have been found hiding under beds during a fire, believing the bed will protect them. All furniture, including beds, is fuel for fires that help increase the speed and intensity of a fire.