Forces and energy (grade 6) · lesson

Three ways heat moves

💡 Heat moves by conduction through touch, by convection in moving fluids, and by radiation across space.

Thermal energy always moves from warmer things to cooler things. Cold does not move. Heat does.

Conduction is heat moving through touch, from particle to particle. A metal spoon in hot soup gets hot this way.

Convection happens in liquids and gases. Warm fluid rises and cool fluid sinks, which makes a current. Radiation is energy carried by light and other waves. It needs no matter, so sunlight can cross empty space.

🧠 Let's work it out

Ask: what is between the hot thing and the cool thing?
If they touch, think conduction.
If a liquid or gas is moving, think convection.
If there is nothing in between, like space, it must be radiation.

What do you think comes next?

conduction: heat moving through things that touch
convection: heat carried by a moving liquid or gas
radiation: energy carried by light and other waves, even through empty space

🔗 PhET simulation: Energy Forms and Changes · PhET Interactive Simulations ↗

Conductors and insulators

💡 Conductors let heat pass quickly, and insulators slow it down.

Metals are good conductors. Heat moves through them fast. That is why a metal pot gets hot all over.

Foam, wool, wood, and plastic are insulators. Heat moves through them slowly. That is why pot handles are often wood or plastic.

You can test materials. Put the same ice cube in cups made of different materials. The ice that lasts longest is in the best insulator.

🧠 Let's work it out

Ice melted in 25 minutes in metal and 90 minutes in foam.

The ice lasted longest in foam.
So foam let the least heat in.

What do you think comes next?

conductor: a material that lets heat pass through easily
insulator: a material that slows the flow of heat

Designing to keep things hot or cold

💡 To keep something hot or cold, block every path heat can take: conduction, convection, and radiation.

Heat can leave soup through the walls of its container. It can also leave with warm air and steam that rise out the top.

A good design blocks each path. Thick insulating walls slow conduction. A tight lid stops warm air from escaping.

Some bottles have two walls with a vacuum between them. A vacuum is empty space with almost no matter. Conduction and convection both need matter to carry heat, so heat cannot cross the empty gap that way.

🧠 Let's work it out

Judge a design by the paths it blocks.
A metal can with a lid blocks moving air but conducts heat.
An open foam cup slows conduction but lets warm air out.

What do you think comes next?

vacuum: a space with almost no matter in it

Energy, mass, and temperature change

💡 How much an object warms up depends on how much energy it gets, how much matter it has, and what it is made of.

Heat flows from a warm object to a cool one until they are the same temperature. The final temperature ends up somewhere in between.

The same energy spread over more matter warms it less. A small cup of water heats up faster than a big pot.

More energy for the same mass means a bigger temperature rise. Also, different materials need different amounts of energy. Water needs much more energy than sand to warm by the same amount.

🧠 Let's work it out

Change one thing at a time.
Same mass, more energy: it gets warmer.
Same energy, more mass: it warms less.
Same mass and same energy, but sand warms more than water: the kind of matter made the difference.

What do you think comes next?

mass: how much matter something has

🔗 Khan Academy: Thermal energy and heat · Khan Academy ↗