Heat Transfer

Heat Transfer

• Heat always moves from a warmer place to a cooler place.

• Hot objects in a cooler room will cool to room temperature.

• Cold objects in a warmer room will heat up to room temperature

What are the different methods of

heat transfer?

• Heat transfers in three ways:

–Conduction

–Convection

–Radiation

Conduction The process that moves heat energy from one object to

another when they are touching physically.

It occurs on solid, liquid, and gas.

How Conduction happens

When you heat a metal strip at one end, the heat
travels to the other end.

As you heat the metal, the particles vibrate, these
vibrations make the adjacent particles vibrate, and so on
and so on, the vibrations are passed along the metal and
so is the heat. Materials that have this ability are called
thermal conductors

Conductors and insulators

Metals: The outer electrons of
metal atoms are free to move.

When the metal is
heated, this ‘sea of
electrons’ gain k_____
energy and transfer it
throughout the metal.

Insulators, such as w___ and p____, do not
have this ‘sea of electrons’ which is why they
do not conduct heat as well as metals.

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Thermal conductors are materials in which thermal energy moves quickly.

Ex. Metal, copper, silver

Why does metal feel colder than wood, if they
are both at the same temperature?

Metal is a conductor, wood is an insulator. Metal
conducts the heat away from your hands. Wood
does not conduct the heat away from your hands as
well as the metal, so the wood feels warmer than
the metal.

Thermal Insulators are material in which
thermal energy moves slowly.

Ex. Rubber, plastic, clothes

Convection
The transfer of thermal energy by the movement of

particles from one part of materials to another. It

occurs in liquids and gases (fluid), but not in solids.

This Photo by Unknown Author is licensed under CC BY-NC-ND

How Convection works

What happens to the particles in a liquid or a
gas when you heat them?

The particles spread out and

become less dense.

This effects fluid movement.

What is a fluid?A liquid or gas.

Fluid movement

Cooler, more d____, fluids
sink through w_____, less
dense fluids.

In effect, warmer liquids and
gases r___ up.

Cooler liquids and gases s___.

Why is it windy at the seaside?

Cold air sinks

Where is the

freezer

compartment

put in a fridge?

Freezer

compartment

It is put at the

top, because
cool air sinks,
so it cools the

food on the
way down.

It is warmer

at the

bottom, so
this warmer
air rises and
a convection

current is

set up.

Radiation
Transfer of thermal energy from one object to another by

electromagnetic waves.

The transfer of thermal energy can be through matter or through space (no matter exist). The transfers are not in contact. Electromagnetic waves carry thermal energy between objects.

How Radiation works

How does heat energy get
from the Sun to the Earth?
There are no particles
between the Sun and the
Earth so it CANNOT
travel by conduction or
by convection.

?

RADIATION

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