HEAT ENERGY AND

TEMPERATURE

HEAT ENERGYHeat energy is due to the movement of

atoms or molecules.As atoms move faster they create more

energy = causing Heat!

THERMAL ENERGY

Depends upon the mass, temperature and phase of an object.

WHAT HAPPENS TO AN OBJECT WHEN IT IS HEATED? Expansion occurs: 1. Particles move faster 2. Particles collide and bounce 3. The substance EXPANDS

Volume Expansion: Liquids take up more space than solids when heated.

Linear Expansion: Solids get longer as they are heated.

CONDUCTOR A material through which Heat can be

easily transferred. Examples: Most metals

INSULATOR A material that is a poor conductor of

heat or energy. Gases, liquids make good insulators

Examples: Plastics (polypropylene), wood, wool, Insulation.

CONVECTION The transfer of heat energy by the

movements of fluids or air at different temperatures.

Examples: Heating a room, Ocean currents, wind

CONVECTION CURRENTS The flow of a fluid due to heated

expansion, followed by cooling and contraction. Occurs in Water only

Example: Gulf stream, Boiling Pot of pasta

CONDUCTION The transfer of energy as heat between

particles as they collide in a substance or The transfer of energy as heat by CONTACT or touch.

Heat always transfers from the hotter object to the colder one.

Examples: placing metal rod in a fire

RADIATION The transfer of heat energy by

electromagnetic waves (LIGHT). Examples: The sun warming the earth,

standing by a fire

TEMPERATURE Definition – The measure of the average

kinetic energy of the molecules in an object.

THERMOMETER A tool that measures temperature –

measures the amount of heat present.

TEMPERATURE SCALES Fahrenheit: Water freezes at 32°F

water Boils at 212°F Body Temp. 100°F

Conversion from F to CC = 5/9 x (F-32)

Celsius : Water freezes at 0°C Water Boils at 100°C Body Temp. 37°CConversion from F to CF = (9/5 x C) + 32

Kelvin Scale = used to measure very low or very high temperatures

Absolute Zero = Temperature at which molecules stop moving O K

HOW DOES A THERMOMETER MEASURE TEMPERATURE? Liquid in the thermometer (either mercury or alcohol) expands and

contracts due to the heat present. Why isn’t water used in thermometers?

WHEN OBJECTS COOL As objects cool down the molecules in

them move more slowly producing less kinetic energy (HEAT), so the objects CONTRACT.

USE OF EXPANSION AND CONTRACTION PROPERTIES IN EVERYDAY LIFE: Bimetallic Strip: 2 different metals

are fused together, one expands faster than the other when heated. As the strip is heated it curls or bends due to the metals.

Bimetallic strips are used in Thermostats to turn them off and on as the metals expand and contract due to heat.

THERMAL SWITCH Safety devices that turn off electricity if circuit gets too hot.

HEAT ENERGY INVOLVED IN CHEMICAL REACTIONS AND STATE CHANGES Heat energy can come from chemical

reactions. Exothermic Reaction – Heat is released -

Feels hot Endothermic Reaction – heat is

absorbed – feels cold