Thermal Energy

• Measurement related to the quantity of molecules.

• the total of all the kinetic and potential energy of all the particles in a substance.

• The flow of thermal energy from one object to another.• Heat always flows from warmer to cooler objects.

•Heat is the result of molecules vibrating quickly.

•Heat is moving energy. Ice gets warmer while

hand gets cooler

Cup gets cooler while hand gets

warmer

Heat and Particle Movement Relationship

• Measure of kinetic energy of molecules

• Thermometer

• Fahrenheit

• Celsius

• Kelvin

Conduction: heat energy travels through solids by vibrating particles

The transfer of heat from one object to another by direct contact between objects or particles.

Examples:Your feet transfer (conduct) heat to a cold tile floor.

A spoon placed in hot soup becomes warmer as the spoon conducts heat away from the hot soup.

Convection: heat energy travels through gases and liquids because the particles move around (current)

• Heat transferred by the movement of molecules within a substance.

• Movement occurs from warmer areas to cooler areas.

• The movement of a substance that is caused by differences in temperature and density.

• Examples: wind boiling water

• Nature wants everything to balance!

Consider this - when you look at the road in the summertime on a hot day, you may notice that the air above the road looks “blurry” – this is convection taking place as the hot air directly over the road absorbs the heat from the road and rises. Although the explanation can be quite complex, convection can help explain why mirages are seen in the desert.

:heat energy travels through waves without a medium – solid, liquid, gas

Heat transferred through

space.

All objects emit (give out)

and absorb (take in) thermal

radiation (heat energy).However materials radiate and

absorb heat better than others.

EXAMPLE:

the sun’s rays causing a sunburn.

Thermal radiation is also known as infrared radiation.

Which color/surface absorbs thermal radiation the best?

Black Shiny gray Matt grey White

Which hand feels hot first?

Why?

Which color of teapot should you put your tea in? Why?

Radiation Conduction Convection

*Transferred in rays or waves

*Energy from the Sun warms the Earth

*Transfer of heat that happens when molecules bump into each other

*Objects must be touching

*Transfer of heat by the flow of material

*In warm air, the molecules move apart, so it is less dense and rises

*In cooler air, the molecules move closer together, so it is more dense and sinks

Example: Example: Example

Review

Which radiates heat better;

black material or silver material?

Which absorbs heat better;

black material or silver material?

Explain choice?

Review

http://open2.net/sciencetechnologynature/worldaroundus/kitchenchaos_embedded.html

Why is it colder in the night than in the day?

• The sun is the greatest heat source in the world.

• As the sun comes up, it warms the world.

• As the sun goes down, the heat is taken away and it cools off.

What will happen to this cold snowman throughout the day as the

sun warms it up?

The warmth of the sun

will cause the snowman

to melt.

What would happen to the temperature of the boiling water in this kettle if ice cubes were added?

The coolness of the ice cubes

would change the temperature

of the water from hot to

lukewarm.

How is the change in temperature of the snowman and the boiling water

related?The temperature of both the snowman and the

boiling water changed to a temperature that

was not really cold or really hot, but rather

somewhere in the middle.

• Conductors are materials that transfer heat easily.

• Conductors hold heat in faster than others

The molecules in a conductor are close

together. This allows the heat to move to all

parts of the pot and the stew in the pot.

Examples:

metals like copper and gold

• An insulator is a material that does not transfer heat easily.

• The molecules in an insulator are far apart. This helps prevent heat from flowing in or out.

• They do not let heat in quickly.

Insulators and conductors

allow us to somewhat control

the flow of heat or the

change in temperature of

objects.