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

Conduction: Heat Through Touch

E2.4 A1.2 A1.4About 50 minutes
Learning goals
  • I can explain conduction using the particle theory.
  • I can sort materials into good conductors and good insulators of heat.
  • I can explain why metal feels colder than wood at the same temperature.
  • I can describe natural processes that depend on conduction.

Words to know

conduction
The transfer of heat through direct contact, as faster-moving particles bump into slower ones and pass on energy.
conductor
A material that lets heat pass through it easily, such as copper, aluminum or iron.
insulator
A material that slows the flow of heat, such as air, wool, wood, plastic, foam or snow.
permafrost
Ground that stays frozen for at least two years in a row. It is common in Canada's North.
blubber
A thick layer of fat under the skin of whales and seals that slows the loss of body heat.

The cold floor mystery

On a winter morning you step out of bed onto a tile floor, and then onto a rug. The tile feels icy. The rug feels warm. But they have been in the same room all night, so they are the same temperature. Why do they feel so different? The answer is conduction.

A bedroom floor where shiny grey tiles meet a thick wool rug with slippers on it.
The tile and the rug are the same temperature. The tile feels colder because it is a better conductor and pulls heat from your feet faster. AI-generated image

How conduction works

Heat can move in three ways: conduction, convection and radiation. This lesson is about the first one.

Conduction is heat transfer by direct contact. Think of a metal spoon in hot soup:

  1. The soup's fast-moving particles bump into the particles at the bottom of the spoon.
  2. Those spoon particles start to vibrate faster.
  3. They bump into their neighbours, which vibrate faster too, and so on up the handle.

The particles themselves stay in place. Only the energy moves along, like a message passed down a line of people. Conduction happens best in solids, where particles are packed closely together. It also happens in liquids and gases, but much more slowly.

heathot endcool endenergy passes particle to particle
Conduction along a metal rod. Particles near the heat vibrate the most. They pass energy to their neighbours, so heat moves along the rod toward the cool end. The particles stay in place.
Good conductors of heatGood insulators (poor conductors)
copper (pots, pipes)air (especially trapped in small pockets)
aluminum (baking sheets, foil)wool, fleece, down feathers, fur
iron and steel (frying pans, radiators)wood, cork
silverplastic, rubber
stone and tile (moderately good)foam, fibreglass insulation, snow
Metals are the best conductors. Materials that trap air are among the best insulators.

Solving the cold floor mystery

Your feet are warmer than the floor. Heat flows from your feet to whatever you stand on.

  • Tile is a fairly good conductor. It carries heat away from your feet quickly, so your feet feel cold.
  • A rug is an insulator with lots of trapped air. It carries heat away slowly, so your feet feel warm.

Your skin senses how fast heat is leaving, not the temperature of the floor. That is also why a metal railing feels much colder than a wooden bench on the same winter day.

footfootTile: a conductorcarries heat away FASTRug: an insulatorcarries heat away slowlyfeels coldfeels warmBoth floors are at the same room temperature.
The arrows show heat leaving your foot. Tile conducts heat away quickly, so it feels cold; the rug's trapped air slows conduction, so it feels warm, even though both are the same temperature.

Conduction in nature

  • Earth's inner heat travels slowly outward through the solid rock of the crust by conduction. Deep mines get hotter the deeper you go.
  • Warming the air: on a sunny day, the ground warms up and heats the thin layer of air touching it by conduction. (Then convection carries that warm air upward, as you will see next lesson.)
  • Snow as a blanket: fresh snow is full of trapped air, so it is a good insulator. A deep snowpack keeps the soil below from freezing as hard, which protects plant roots. Mice and voles live in tunnels under the snow, where it stays much warmer than the frigid air above.
  • Permafrost: in Canada's North, the ground stays frozen for years. Heat conducted down from warmer air in summer thaws only the top layer. As the climate warms, more heat is conducted into the ground and permafrost is thawing in many places, which can damage roads and buildings.
  • Lake ice: ice and snow on a lake slow the loss of heat from the water below, so the lake does not freeze solid.
  • Animals: fur, feathers and blubber are insulators that slow conduction of body heat to the cold air or water. Seals and whales keep warm in icy water with thick blubber. Birds fluff up their feathers to trap more air.
Worked example

Let's explain: the metal railing and the wooden bench

On a −10 °C day, a metal railing and a wooden bench in a park are both at −10 °C. Which feels colder to your bare hand, and why?

  1. Your hand (warmer) touches something colder, so heat flows out of your hand by conduction.
  2. Metal is a good conductor: it carries heat away from your hand quickly.
  3. Wood is an insulator: it carries heat away slowly.
  4. Your skin feels the rate of heat loss, so faster loss feels colder.

The metal railing feels colder, even though both are the same temperature, because metal conducts heat away from your hand faster. (Never touch frozen metal with a wet hand or your tongue: it can stick to your skin.)

Just for fun

Why are metal spoons always invited to parties?

They're great conductors: they keep the energy moving!

Hands-on activity

Conductor race: which spoon gets hot first? (A1.2)

You need: a large mug, hot tap water, a metal spoon, a plastic spoon and a wooden spoon of about the same length, a little butter (or margarine), 3 small dried beans or frozen peas, a clock, and a grown-up.

  1. Put a tiny dab of butter near the top end of each spoon's handle. Stick one bean or pea onto each dab.
  2. Predict: which bean will slide off first? Last?
  3. A grown-up fills the mug with hot tap water.
  4. Stand all three spoons in the mug at the same time, with the beans at the same height above the water. Start timing.
  5. Record when each bean slides off (stop at 10 minutes).

Fair test: keep the same water, the same height of beans and the same amount of butter. Change only the material of the spoon.

What to look for: the bean on the metal spoon usually falls first, because metal is a good conductor. The plastic and wooden spoons may not get warm enough at all in 10 minutes.

Safety (A1.4): only a grown-up pours hot water; use hot tap water, never boiling water. Do not touch the metal spoon after it has been in the water; let it cool. Keep beans and peas away from young children (choking hazard). Wipe up spills.

Your turn

1

What is conduction?

2

During conduction along a spoon, do the particles travel up the handle? Explain.

3

In which state of matter does conduction happen best? Why?

4

Name three good conductors of heat.

5

Name three good insulators.

6

Why does a tile floor feel colder than a rug in the same room?

7

How does snow help plants survive winter?

More practice: warm-up

1

Is aluminum foil a conductor or an insulator of heat?

2

Why are many pot handles made of plastic or wood?

3

What do whales and seals have that slows heat loss in cold water?

4

Why do birds fluff up their feathers on cold days?

5

What is permafrost?

More practice: on your own

1

Explain why a cast-iron frying pan is good for cooking, using the word conductor.

2

Why should you never touch a frozen metal pole with your tongue in winter?

3

A deep mine in northern Ontario gets warmer the deeper the miners go. Which type of heat transfer brings Earth's inner heat up through the rock?

4

In the spoon race, Jamal used hot water for the metal spoon and warm water for the wooden spoon. Is this a fair test? Explain.

5

Why can thawing permafrost damage roads and buildings in the North?

Challenge

1

A winter jacket filled with down is very warm when dry but much less warm when it gets soaking wet. Use conduction to explain why.

2

A pot has a copper bottom and a steel body. Why might cookware makers put copper on the bottom?

3

Design a better spoon-race test: how could you measure exactly how fast each spoon warms up, instead of using butter and beans?

Check your understanding

Quiz

1.

Conduction is heat transfer...

2.

Which material is the best conductor of heat?

3.

Why does a metal railing feel colder than a wooden bench at the same temperature?

4.

Why is snow a good insulator?

5.

During conduction, the particles of a solid...

6.

What helps seals stay warm in icy water?

For parents and teachers

Big idea (E2.4): conduction is heat transfer by direct contact; energy passes from particle to particle while the particles stay in place. Metals conduct well; trapped air, wool, foam and snow insulate. Natural processes include Earth's heat moving through rock, snow insulating soil, permafrost and animal insulation. The spoon race is a fair test (A1.2) with heat safety (A1.4).

How to help: compare how different surfaces feel in the same room (a metal doorknob, a wooden table, a wool blanket) and talk about why. In winter, point out how snow-covered gardens survive.

Common difficulties:

  • Thinking metal is colder than wood at the same temperature. It only feels colder.
  • Thinking particles travel during conduction. Only energy moves.

Safety: an adult pours the hot tap water (never boiling). Metal spoons can get hot. Beans and peas are a choking hazard for young children. Remind children never to put their tongue on frozen metal.