What is Heat?Heat is the transfer of thermal energy from

one object to another object, when the objects have different temperatures.

Thermal Energy

Energy always flows from a warmer object to an object with a lower, colder temperature.

Energy from the sun reaches Earth’s surface and heats objects such as roads, rocks, and water.

Molecules in Motion!• Temperature = the

average kinetic energy of moving molecules

• Heat energy = the energy transferred from one object to another

• Internal energy = total energy of an object

Solar Energy

Energy from the sun is radiated into space: absorbed by the Earth’s crust and transferred throughout our atmosphere!

Radiant Energy

The sun’s heat is transferred into the atmosphere in 3 different ways:

Radiation Conduction Convection

Radiation:

Energy from the sun is transferred in the form of electromagnetic rays or waves.

Radiant energy from the sun warms your face.

Three Ways to Transfer Heat

f Convection - heat energy flow through a current (in fluids)

f Radiation - by infrared waves: a medium is NOT needed!

f Conduction - when a warm substance touches a colder one

Heat is conducted from the pan to the steak.

Heat energy flows through the air by convection.

Heat is radiated to the campers from the fire.

Heat Transfer and Climatef Heat from the sun

reaches the earth by radiation.

f The earth’s surface warms the air by conduction.

f Convection currents in the air and water cause weather patterns.

Conduction:Transfer of energy that

occurs when molecules bump into one another.

(Molecules are always in motion but molecules with higher temperatures move faster then those in objects with slower, cooler temperatures)

Conduction - Convection

Convection:

Circulates heat throughout the atmosphere through the flow of materials

When the atmosphere becomes warmer, cooler, denser air sinks and warmer, less dense air rises forming a convection current.

Earth’s: Internal ConvectionSuper heated magma rises to the surface of

our planet, while the cooler, denser magma sinks to be continuously reheated.

Tell if the following is radiation, conduction or convection:

Walking along a hot beach, the sand heats up your feet and they feel as if they are burning.

While riding in a convertible you feel the sun on your face

Floor one of an apartment complex has a lower air conditioning bill than floor seven.

Heat and Matterf A change in heat energy is needed for any phase change.

f During a phase change, the substance’s internal energy changes, but the temperature does not.

f The boiling point of a substance is the temperature where it changes from a liquid to a gas.

f The melting point of a substance is the temperature where it changes from a solid to a liquid.

Temperature as a function of Time

-50

0

50

100

0 2 4 6 8 10

Thermal Expansionf Solids, liquids, and

gases all expand (get bigger) when they get hotter.

f As molecules get more heat energy, they move faster, and push each other farther apart.

f When substances lose heat energy, they contract (get smaller). Bridges and sidewalks have built-in expansion joints to

prevent them from deforming or cracking due to thermal expansion or contraction.