• Heat is thermal energy that is transferred from one object to another when the objects are at different temperatures.

Heat and Thermal Energy

2

• The amount of heat that is transferred when two objects are brought into contact depends on the difference in temperature between the objects.

• When heat is transferred, thermal energy always moves from warmer to cooler objects.

Transfer of Heat

2

• Heat never flows from a cooler object to a warmer object.

Heat

• This process of heat transfer can occur in three ways:

—conduction, radiation, or convection.

• Transfer of heat by direct contact is called conduction.

Conduction

• Conduction occurs when the particles in a material collide with neighboring particles.

• Imagine holding an ice cube in your hand.

Conduction

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• The faster-moving molecules in your warm hand bump against the slower-moving molecules in the cold ice.

Heat

• Heat flows from your warmer hand to the colder ice, and the slow-moving molecules in the ice move faster.

Conduction

2

Heat

• Conduction usually occurs most easily in solids and liquids, where atoms and molecules are close together.

Conduction

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• Then atoms and molecules need to move only a short distance before they bump into one another and transfer energy.

Aim: Thermal Energy

DO NOW:

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• What 2 things define the state of matter?
• When the temperature of an object is increased, what happens to the molecules?
• When heat is transferred, thermal energy always moves from....
• Heat transfer occurs by what 3 ways?
• Gas to Solid = ?
• Solid to Gas = ?

• Heat is transferred from the Sun to Earth by radiation.

Radiation

2

• Heat transfer by radiation occurs when energy is transferred by electromagnetic waves.

• The Sun is not the only source of radiation.

• All objects emit electromagnetic radiation, although warm objects emit more radiation than cool objects.

• The warmth you feel when you sit next to a fireplace is due to heat transferred by radiation from the fire to your skin.

• In a gas or liquid, molecules can move much more easily than they can in a solid.

Convection

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• As a result, the more energetic molecules can travel from one place to another, and carry their energy along with them.

• This transfer of thermal energy by the movement of molecules from one part of a material to another is called convection.

• As a pot of water is heated, heat is transferred by convection.

• First, thermal energy is transferred to the water molecules at the bottom of the pot from the stove.

• These water molecules move faster as their thermal energy increases.

• Because the molecules are farther apart in the warm water, this water is less dense than the cooler water.

Transferring Heat by Convection

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• As a result, the warm water rises and is replaced at the bottom of the pot by cooler water.

• The cooler water is heated, rises, and the cycle is repeated until all the water in the pot is at the same temperature.

• Natural convection occurs when a warmer, less dense fluid is pushed away by a cooler, denser fluid.

Natural Convection

2

• Wind movement near a lake or ocean can result from natural convection.

• Air is heated by the land and becomes less dense.

• Denser cool air rushes in, pushing the warm air up.

• The cooler air then is heated by the land and the cycle is repeated.

• Forced convection occurs when an outside force pushes a fluid, such as air or water, to make it move and transfer heat.

Forced Convection

Aim: Thermal Energy

DO NOW:

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What 2 states does conduction occur?

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What 2 states does convection occur?

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