Understanding Heat Transfer, Conduction, Convection and

Radiation

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.

Question

• If a cup of coffee and a red popsickle were left on the table in this room what would happen to them? Why?

• The cup of coffee will cool until it reaches room temperature. The popsickle will melt and then the liquid will warm to room temperature.

Heat Transfer Methods

• Heat transfers in three ways:

– Conduction

– Convection

– Radiation

Conduction

• Conduction is when heat moves between objects that are touching.

• Example: Cooking an egg on the stove. – The heat from the burner makes the pan hot. Soon,

the thermal energy moves through the hot pan to the cold egg. The egg gains thermal energy from the pan. Eventually, the egg and the pan are the same temperature.

• Can you think of another example?

Conduction

• A pan is used for cooking because it is made of metal, such as iron or copper.

• Thermal energy moves easily through most metals.

• An object that thermal energy can move through easily is called a conductor.

Which of the following items are good conductors?

Convection• Convection is when heat moves between

objects that ARE NOT touching.

• The thermal energy is carried from one object to the other by a gas.

• Example: Cooking chicken in the oven,– You put the chicken in a hot oven. The gasses that

heat up the oven are moving all around the chicken, causing the thermal energy to transfer to the chicken and cooking it. The chicken never directly touches the coils that heat the oven, but the gas from the coils does.

Convection• Can you think of some other examples?

– Cooking food in the microwave– Air conditioner and heat in your house

Radiation• Radiation is the transfer of thermal energy by

electromagnetic waves.

• What does that mean? It means that radiation does not require matter (solid, liquid, or gas) to transfer thermal energy.

• Example: the sun– You can feel the heat from the sun’s rays. You are

not touching the sun and no gases are touching the sun and then you.

The third method of heat transfer

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

Radiation• What are some other examples of radiation?

– A fire– A light bulb

• For radiation to be felt as heat, it must first be absorbed by a material

• This is why your clothes feel hot after being in the sun or after sitting in front of a fire.

1. Which of the following is not a method of heat transfer?

A. Radiation

B. Insulation

C. Conduction

D. Convection

2. How does heat energy reach the Earth from the Sun?

A. Radiation

B. Conduction

C. Convection

D. Insulation

3. An example of convection is________.

A. Heating up pizza in the ovenB. Your skin getting warm in the sunC. Cooking eggs on the stove

D. None of the above

4. An example of conduction is _________.

A. Your skin getting warm in the sunB. Cooking eggs on the stove

C. Heating up pizza in the oven

D. None of the above

• Conduction—when thermal energy moves between objects that are touching.

• Convection—when thermal energy moves between objects that are not touching by liquids or gases

• Radiation—the transfer of thermal energy by electromagnetic waves through empty space, such as the sun.

• Conductor—An object that thermal energy can move through easily