Grade by Grade
E. Earth and Space Systems · Heat in the Environment

Where Does Heat Come From? Ways Heat Is Generated

E2.2 A1.1 A3.1About 45 minutes
Learning goals
  • I can describe several ways heat is generated: nuclear, chemical, mechanical (friction), electrical and from Earth's interior.
  • I can identify the energy change that produces heat in everyday devices and natural events.
  • I can explain that many energy changes produce some heat that is not wanted.
  • I can name jobs, including skilled trades, that work with heat.

Words to know

energy transformation
When energy changes from one form to another, for example electrical energy changing to thermal energy in a toaster.
nuclear fusion
When tiny particles at the centre of atoms join together, releasing huge amounts of energy. It powers the Sun.
nuclear fission
When the centre of a large atom, such as uranium, splits apart, releasing energy. Used in nuclear power stations.
combustion
Burning: a chemical reaction in which a fuel combines with oxygen and releases heat and light.
friction
A force that resists motion when two surfaces rub together. It turns some energy of motion into thermal energy.
geothermal energy
Heat from inside Earth.
cellular respiration
The chemical process in living cells that uses food and oxygen to release energy, including body heat.

Remember from Grade 5

In Grade 5 you learned that energy comes in many forms (light, sound, electrical, chemical, mechanical, thermal) and that energy changes form but is never created or destroyed. You also saw that many energy changes "lose" some energy as heat that spreads out.

Now you will look closely at the many ways heat is generated: where the thermal energy that warms us, cooks our food and shapes our planet actually comes from.

Heat is energy that changed form

Heat does not appear from nowhere. It is always made when another form of energy changes into thermal energy. Scientists group the main sources like this:

Looking down into a toaster whose heating wires glow bright orange, with two slices of bread beside it.
In a toaster, electrical energy changes into thermal energy. The wires get so hot they glow. AI-generated image
SourceEnergy changeExamples
Nuclearnuclear energy → thermal energy (and light)The Sun (nuclear fusion); nuclear power stations such as Ontario's Bruce and Darlington stations (nuclear fission)
Chemicalchemical energy → thermal energyBurning wood, natural gas or gasoline; your body releasing energy from food; a compost pile warming up; air-activated hand warmers
Mechanical (friction)energy of motion → thermal energyRubbing your hands together; bike brakes; sandpaper getting warm; a drill bit getting hot
Electricalelectrical energy → thermal energyToasters, kettles, hair dryers, electric baseboard heaters, old-style light bulbs
Earth's interiorEarth's stored internal heat (geothermal energy)Volcanoes, hot springs (like the ones at Banff, Alberta), hot rock deep underground
The main ways heat is generated.
THERMALENERGYNuclearthe SunChemicalburning, foodMechanicalfrictionElectricaltoaster coilsEarth's interiorhot springs
Five sources, one result. Every source of heat is another form of energy changing into thermal energy; heat never appears from nothing.

A closer look

Nuclear. The Sun is a giant ball of hot gas. Deep in its core, tiny particles join together (fusion), releasing enormous energy that reaches Earth as light and heat. Nuclear power stations split uranium atoms (fission). The heat boils water to make steam that spins turbines to make electricity.

Chemical. In combustion, a fuel combines with oxygen and releases heat and light. Inside your cells, cellular respiration releases energy from food more slowly, which keeps your body near 37 °C. In a compost pile, tiny living things (bacteria and fungi) break down plant material and release heat, so a large, active compost pile can feel warm inside, even on a cool fall day. Some hand warmers contain iron powder that reacts with oxygen in the air and gives off heat.

Mechanical. When surfaces rub, friction turns some energy of motion into thermal energy. This is why your hands get warm when you rub them and why brakes get hot. Squeezing air quickly in a bike pump also warms it.

Electrical. When electric current flows through a wire that resists it (like the coils in a toaster), the wire heats up and can glow.

Earth's interior. Earth is very hot inside. Some of this heat is left over from when Earth formed, and some is made as radioactive materials in rocks slowly break down. It reaches the surface in volcanoes, hot springs and geysers.

Uraniumatoms split(fission)HeatboilswaterSteamspins aturbineGeneratormakeselectricityInside a nuclear power stationnuclear energy → thermal energy → energy of motion → electrical energy
In a nuclear power station, the heat from splitting uranium atoms is used to boil water. The steam spins a turbine, and a generator turns that motion into electricity.

Wanted heat and unwanted heat

Sometimes heat is the goal (a furnace, a kettle). Often it is a side effect: a laptop gets warm, a car engine gets hot, a phone warms up while charging. That unwanted heat usually spreads into the surroundings and cannot easily be used again. Engineers work hard to reduce it, because it is wasted energy.

Worked example

Let's identify the energy change

For each, name the source of heat and the energy change: (a) a campfire, (b) a hair dryer, (c) your hands after rubbing them, (d) a hot spring, (e) a sunny sidewalk.

  1. (a) Wood burns: chemical energy → thermal energy and light.
  2. (b) Current flows through a heating coil: electrical energy → thermal energy (and motion energy in the fan).
  3. (c) Friction between your palms: energy of motion → thermal energy.
  4. (d) Water is heated by hot rock underground: Earth's internal (geothermal) heat.
  5. (e) Sunlight is absorbed by the sidewalk. The light came from nuclear fusion in the Sun.

(a) chemical, (b) electrical, (c) mechanical/friction, (d) Earth's interior, (e) nuclear (the Sun).

Just for fun

Funny but true: the middle of a big, busy compost pile can reach about 60 °C, hotter than a hot tub. Your banana peels are basically throwing a very warm party in there.

People who work with heat (A3.1)

Many careers, including skilled trades, use knowledge of how heat is generated:

  • Welders use the intense heat of an electric arc or a gas flame to melt and join metals.
  • Heating, ventilation and air-conditioning (HVAC) technicians install and repair furnaces, boilers and heat pumps.
  • Chefs and bakers control heat to cook food safely.
  • Firefighters understand how fires start, spread and can be put out.
  • Nuclear operators and engineers run the reactors that heat water to make much of Ontario's electricity.
Hands-on activity

Heat hunt: where is heat generated in your home? (A1.1)

You need: paper, a pencil and a grown-up to walk around with you.

Part 1: Rub test

  1. Put your palms on your cheeks. Notice how warm they feel.
  2. Rub your palms together quickly for 15 seconds. Put them on your cheeks again.
  3. Try rubbing for 30 seconds. What changes?

What to look for: your palms feel warmer after rubbing, and warmer still after rubbing longer. Friction changed energy of motion into thermal energy.

Part 2: Heat hunt

  1. Make a table with three columns: Object or place, Source of heat, Wanted or unwanted heat?
  2. Walk through your home and find at least 8 examples of heat being generated. Look at appliances, devices, people, pets and sunny windows. Check outside too (the Sun, a car that was just driven).
  3. For each, name the source: nuclear (the Sun), chemical, mechanical, electrical or Earth's interior.

Research question (A1.1): find out how your home is heated in winter (ask a grown-up or look at the furnace or heater). What energy change does it use?

Safety: look, don't touch. Never touch a stove, oven, toaster, kettle, iron, space heater, fireplace or car engine to test whether it is hot. Never put anything into a toaster or outlet. Stay with your grown-up.

Your turn

1

Name the five main ways heat is generated that you learned in this lesson.

2

What process produces the Sun's energy?

3

What energy change happens in a toaster?

4

Why do your hands get warm when you rub them together?

5

How does your body make heat?

6

Give one example of unwanted heat from a device.

7

What two things make Earth's interior hot?

More practice: warm-up

1

What kind of energy is stored in wood, gasoline and natural gas?

2

Burning is also called ______.

3

Name a natural place where heat from Earth's interior reaches the surface.

4

What metal is split in a nuclear power station?

5

Name one skilled trade that works with heat.

More practice: on your own

1

A mountain biker brakes hard down a long hill. Afterward the brake discs are hot. Explain where the heat came from.

2

Why can the inside of a large compost pile be warm even on a cool day?

3

Sort these as wanted or unwanted heat: an electric kettle, a game console, a furnace, a car engine.

4

How is a nuclear power station like a coal-burning power station, and how is it different?

5

Explain why the energy in sunlight that warms a sidewalk in Sudbury started as nuclear energy.

Challenge

1

An old-style light bulb turns only a small part of its electrical energy into light; most becomes heat. An LED bulb gives the same light with much less electricity. Why does this matter for energy use?

2

A runner's body temperature rises during a race. Use the idea of energy transformation to explain why.

3

Plan a fair test to find out whether rubbing your hands faster makes them warmer. What would you change, keep the same and measure?

Check your understanding

Quiz

1.

What energy change happens when a log burns?

2.

What powers the Sun?

3.

Rubbing two sticks together makes them warm because of...

4.

Which of these is heat from Earth's interior?

5.

A phone gets warm while charging. This heat is...

6.

How does your body produce heat?

For parents and teachers

Big idea (E2.2): heat is generated when other forms of energy (nuclear, chemical, mechanical, electrical, Earth's internal heat) change into thermal energy. The heat hunt is a small research task (A1.1), and the careers section connects to skilled trades (A3.1).

How to help: walk through the heat hunt together and talk about each device. Ask how your home is heated (natural gas furnace, electric baseboards, heat pump, wood stove, oil) and which energy change it uses.

Common difficulties:

  • Thinking the Sun is "burning" like a fire. The Sun's energy comes from nuclear fusion, not combustion.
  • Forgetting living things make heat. Bodies and compost piles release heat from chemical reactions.

Safety: during the heat hunt, children should look but never touch appliances, stoves, heaters or engines.