CHAPTER 2; SECTION 2Heat transfer

THINK ABOUT IT…

If you add ice to lemonade on a hot summer’s day why does the ice melt? Choose the best answer:A. The coldness from the ice moved into the lemonade

B. The heat from the lemonade moved into the ice

C. The coldness and heat moved back and forth until the lemonade cooled off

The correct answer is B. The heat from the lemonade moved into the ice.

Heat energy is transferred from one place to another through the process of heat flow.

This thermal energy will only move from a warmer object to a cooler object, never the other way around.

Heat went into the ice from the lemonade, cooling the lemonade and melting the ice

HEAT CAN BE TRANSFERRED IN 3 WAYS:

RADIATION

The flow of energy through space and matter.

Examples include visible light, radio waves, and radiant heat.

Can be in the form of particles or waves.

EXAMPLES OF RADIATION (HEAT)

CONVECTION

The transfer of heat by a liquid or gas (such as air).

Can only occur in liquids and gases (relatively big spaces between the molecules)

A convection current is where hot air rises and cold air sinks.

WHY DOES HEAT RISE?

Molecules that are heated move around faster, causing them to spread apart (the AIR expands, not the molecules)

This causes the air to be less dense (and less heavy), so it rises

When air rises, it will cool off and become more dense (the air condenses), so it will fall down again.

EXAMPLES OF CONVECTION

CONDUCTION

The direct transfer of heat from one substance to another substance that is touching it.

Molecules can pass heat energy to adjacent molecules, heating them as well

Conduction works better it certain substances, like metals

EXAMPLES OF CONDUCTION

ALL 3 TYPES WORK TOGETHER:

HEATING IN THE TROPOSPHERE

How does each type of heat transfer heat the Earth?

See page 51 in book