CHAPTER 6: THERMAL ENERGY

Section 1—TEMPERATURE AND HEAT

What is temperature?

The temperature of an object is related to the average kinetic energy of the atoms or molecules.

These particles move quickly when hotThese particles move slowly when cold↑ KE = ↑ TEMPERATUREThe SI unit for temperature is the Kelvin (K)

REMEMBER…

Kinetic energy is energy in the form of motion. KE depends on the mass and the velocity of an object.

MASS—how much matter is in an objectVELOCITY—speed and direction of an object

MATTER

All matter is made of tiny particles—atoms and molecules.

Atoms make up molecules and are held together by chemical bonds.

In all materials---solids, liquids, or gases, these particles are in constant motion.

THERMAL ENERGY

The sum of the kinetic and potential energy of all molecules in an object is the thermal energy of the object.

↑ SPEED of the molecules = ↑ KE

↑ DISTANCE (separation) = ↑ PE

The transfer of THERMAL ENERGY

Heat always flows from warmer to cooler objects.

Examples— A cup of hot chocolate/your cold hands Warm air/cold stick of butter

A COLD STICK OF BUTTER

Because the air in the room is a higher temperature than the butter, molecules in the air have more KE than the butter molecules.

Energy is transferred from faster-moving molecules in the air to slower-moving butter molecules.

The transfer of THERMAL ENERGY (continued)

The butter molecules then begin to move faster and the temperature of the butter increases.

↑ temperature = ↑ thermal energy (KE) (KE + PE)

HEAT

HEAT is THERMAL ENERGY that flows from something at a higher temperature to something at a lower temperature.

Example—CHAIRThermal energy from a person’s body flowed to the chair and increased the temperature of the chair.

HEAT

Heat is a form of energy, so it is measured in joules—the same unit that energy is measured in .

Heat always flows from warmer to cooler materials.

SPECIFIC HEAT

The amount of heat that is needed to raise the temperature of 1 kg of some material by 1°C or 1 K is called the specific heat of the material.

Specific heat is measured in joules per kilogram Kelvin or J/kgK.

SPECIFIC HEATWATER VS. SAND

WATER = ↑ SPECIFIC HEATSAND = ↓ SPECIFIC HEAT

Compared to 1 kg of sand, the amount of heat that is needed to raise the temperature of 1 kg of water by 1 °C is about 6 times greater.

So…the ocean water at the beach would have to absorb 6 times as much heat as the sand to be at the same temperature.

WATER AS A COOLANT

Because water can absorb heat without a large change in temperature, it is useful as a coolant.

A coolant is a substance that is used to absorb heat.

CHAPTER 6: THERMAL ENERGY

Section 2—Transferring Thermal Energy

CONDUCTION

Thermal energy travels as heat from a material at a higher temperature to a material at a lower temperature.

The transfer of thermal energy from matter by the direct contact of particles is called CONDUCTION.

CONDUCTION

CONDUCTION (continued)

Examples—making a snowball; drinking a cup of hot chocolate

(DIRECT CONTACT)***CONDUCTION occurs because all matter is

made up of atoms and molecules that are in constant motion.

CONDUCTION (continued)

Heat can be transferred by conduction from one material to another (SOUP TO SPOON) or through one material (FROM ONE END OF THE SPOON TO THE OTHER END).

CONDUCTION (continued)

Although, CONDUCTION can occur in solids, liquids, and gases---solids usually conduct heat much more effectively

CONDUCTION (continued)

Why do you think most cooking pots are made of metal, but the handles usually are not?

Silver, copper, and aluminum are among the best heat conductors.

Wood, plastic, glass, and fiberglass are poor conductors of heat.

CONVECTION

One way liquids and gases differ from solids is that they can flow. Any material that can flow allows fluids to transfer heat in another way—CONVECTION.

CONVECTION (continued)

CONVECTION is the transfer of energy in a fluid by the movement of the heated particles.

Example—Earth’s atmosphere is made of various gases and is a fluid. The atmosphere is warmer at the equator than at the poles.

CONVECTION (continued)

Also, the atmosphere is warmer at Earth’s surface than higher altitudes.

These temperature differences create convection currents that carry heat to cooler regions.

RADIATION

Earth gets heat from the Sun, but how does that heat travel through space?

***Almost no matter exists in the space between Earth and the Sun, so heat cannot be transferred by CONDUCTION OR CONVECTION. Instead, the Sun’s heat reaches the Earth by RADIATION.

RADIATION is the transfer of energy by electromagnetic waves.

Energy that is transferred by radiation is often called RADIANT ENERGY.

TRANSFERRING THERMAL ENERGY

RADIATION VS. COLORS OF MATERIALS

Light-colored clothing---reflects more radiant energy

Dark-colored clothing---absorbs more radiant energy

INSULATORS

A material that does not allow heat to flow through it easily is called an INSULATOR.

Materials such as wood, plastic, and fiberglass are good insulators and therefore, are poor conductors of heat.

INSULATORS (continued)

Gases, such as air, are usually better insulators than solids or liquids.

A material that is a good conductor of heat, such as a metal, is a poor insulator.

Air = good insulator, poor conductor

BUILDING INSULATION

Building insulation is usually made of fluffy material, such as fiberglass, that contains pockets of trapped air. Reduces flow of heat between building and the

air outside Helps furnaces and air conditioners work more

effectively, saving energy

INSULATING MATERIALS

INSULATING MATERIALS

CHAPTER 6: THERMAL ENERGY

Section 3—Using Heat

All heating systems require some source of energy.

What is the simplest and oldest heating system?

Wood or coal burned in a stove Advantage—cheap Disadvantage—heat transfer to others

rooms is slow

FORCED-AIR SYSTEM

Most common--PHS

Fuel is burned in a furnace and heats air; fan blows warm air through ducts in each room

CONVECTION CURRENT

RADIATOR

Closed metal container that contains hot water or steam.

Fuel is burned in a central furnace and heats a tank of water; pipes carry the hot water to radiators that are located in each room.

ELECTRIC BASEBOARD

No central furnace Cost more than electric

heat pump Walls/floors not able to

include pipes/ducts

SOLAR HEATING

The energy from the Sun is called solar energy.

Advantage—free, endless supplyDisadvantage—depends on

location/weather

PASSIVE SOLAR HEATING

No mechanical devices House/building faces

the South (lots of windows on the South sunny side)

Cheap

ACTIVE SOLAR HEATING

Uses devices called solar collectors; heat air or water and then circulate it through the house

Expensive

ACTIVE—SOLAR PANELS

SOLAR HEAT (ACTIVE AND PASSIVE)