Chapter 7: HEAT

1) Heat is a form of energy. The SI unit is joule, J2) When heat energy is supplied to a substance,

the temperature of the substance will rise.3) Heat flows from a hotter to a colder place.

This process of heat transfer will stop when the temperature of the 2 places become the same.

4) Sources of heat:

7.1 Heat as a form of energy

Sources of heat

Burning can

produce heat

2 objects hitting

each other can produce

heat

Rubbing or

friction between 2 objects

can produce

heat

5) Useful of heat: a) drying b) ironing c) cooking d) keeping warm

Temperature1) Temperature is the measure of the degree of

hotness or coldness of an object.2) A thermometer is used to measure

temperature. The SI unit of temperature is the kelvin, (K). However, the commonly used unit is degree Celsius (0C).

3) Hot substances have high temperatures whereas cold substances have low temperatures.

4) The difference between heat and temperature:

Heat

A form of energy

Can do work

SI unit = Joule (J)

Temperature

A measure of the hotness or coldness of

an object

Cannot do work

SI unit = kelvin (K)

5) 3 types of thermometers:

Type of thermometer

Mercury in glass laboratory

thermometer

Clinical thermometer

Alcohol in glass thermometer

Range temperature

-10 0C and 110 0C

35 0C and 42 0C

-117 0C and 78 0C

Use

Measures temperature when doing experiments

Measures body temperature

Measures very low temperatures

Is heated

Particles absorb heat

Particles receive energy and move faster

The distance between the particles increase

The volume of the matter increases

The matter expands

Is cooled

Particles release heat

The particles lose energy and move more slowly

The distance between the particles decreases

The volume of the matter decreases

The matter contracts

Matter7.2 The effectof heat flow on matter

Expansion and Contraction (Solids)1) A solid expands when it is heated. It contract

when it is cooled.

2)The expansion of solid can be shown by a metal ball.3) Different metals expand at different rates:

Aluminium

Brass expansion increases Copper

Iron

Invar

4) Different metals expand unequally when heated to the same temperature. This can be explained by heating bimetallic strip.

Brass

Iron

Heated

* When heated, showing that brass expands more than iron

Heated

* When heated, showing that aluminium expands more than copper

Aluminium

Copper

Expansion and Contraction (Liquids)1) A liquid expands when it is heated. It contract

when it is cooled.

2) Different liquids expands and contract at difference rates

Benzene

Alcohol increases Water expand

Mercury

Expansion and Contraction (gases)1) Gases expands when it is heated and contract when cooled.

2) Different gases expands at the same rate.

Transfer of Heat1) Heat can be transferred from a hot to a cold place by the

process of :

a) Conductionb) Convectionc) Radiation

CONDUCTION1) Conduction is the transfer of heat energy between

neighboring molecules in a substance. It takes place from a region of higher temperature (hot) to a region of lower temperature (cold).

2) When one part of an object is heated, its get hot. The particles there gain heat energy making them vibrate stronger. They then collide and pass some heat energy to the neighbouring particles.

Iron rod

Heat transfer

CONVECTION1) Convection is the transfer of heat in fluids (liquids

and gases) carried out by moving particles.

2) Hot fluids become less dense and move upwards.

Cold fluids that are denser move down to replace the hot fluids.

3) A convection current is produced.

Convection in liquid

Convection

RADIATION1) Radiation is the transfer of heat without involving a

medium.

2) Radiation can take place through air space or a vacuum.

3) Radiation heat moves at the speed of light.

4) Radiation heat can be absorbed or reflected

Conduction

Solid

No

SlowHeat is transfer

from particle to

particle through

vibration

Convection

Fluid (liquid or gas)

No

Faster than conductionHeat is brought by the heated particles

that move upwards

Radiation

Solid, liquid or gas / no

medium

Yes

Very fastHeat moves in the form of waves in a straight

line

Comparison between conduction, convection and radiation

Medium

Take place in Vacuum

Speed

Way heat is transfer

Heat Flow in Natural Phenomena

1) LAND BREEZE 1) Land breeze blow during the night.

2) At night , the land loses heat faster than the sea.

3) The land become cooler than the sea.

4) The warm air above the surface of the sea (less dense) rises. The cool air above the land (denser) flow to the sea

2) SEA BREEZE1) Sea breeze blow during the day.

2) During the day, the land heats up faster than the sea.

3) The air on surface of the land become warm (less dense) and rises .

4) The cooler air over the sea (denser) flows in to take place of the warm air.

HEAT CONDUCTOR

1) Substance that conduct heat are called heat conductor.

2) Some substances conduct heat readily – (good heat conductor)

3) All metal such as iron, magnesium, aluminium and zinc are good conductors of heat.

Copper Aluminium Brass best conductor Zinc Tin Iron Lead

Uses of heat conductors

Cooking utensil ( kettles, pots, pans) aremade from metals. Food can be cooked quickly or water can be boiled quickly.

Mercury in the bulb expands and contracts easily.

1)2)

ThermometerCooking utensils

Electric iron3)

The bottom of an electric iron ismade up of metals so that it can heat up quickly

HEAT INSULATOR

1) Substance that conduct heat poorly are called insulators

2) Non-metal such as glass, wood, cork, air, water and wool are insulators.

3) Fluids (liquid, gas) are poor conductors of heat.

Uses of heat insulators.

1) Handles of kettle

Handles of kettles, irons and cooking utensils such as pots andfrying pan are made of woodor plastic

Application of the principle of convection in daily life

1) Ventilation of building

a) The hot air in the building will flow out through the ventilation holes at the top. The cold air enters

through the holes (windows/door) on the lower part.

2) Refrigerator

a) Cold air from the freezer compartment at the top moves down to the lower part of the refrigerators. The hot air is moved up.

3) The cooling system in a car (radiator of the car)

a) The water around the engine becomes hot when the engine moves. Hot water flows up through the radiator and gets cooled. The cold water moves down and flows back around the engine.

1) Matter exists in solids, liquids and gases. Matter can change from one state to another. Eg: Solid can be change to a liquid by heating. (heat absorb) A liquid state can be change to a solid by cooling. (heat release)

7.3 Effect of Heat on Matter

Freez

ing

Mel

ting

Evaporation/

boiling

Condensati

on

Sublimation

Sublimation

Liquid

GasSolid

Process

Condensation

Melting

Freezing

Evaporation/Boiling

Sublimation

Sublimation

Change in state

Gas-liquid

Solid-liquid

Liquid-solid

Liquid - gas

Solid-gas

Gas-solid

Absorb/ release heat

Release heat

Absorb heat

Release heat

Absorb heat

Absorb heat

Release heat

The change in the state of matter.

Melting (pg 112-113)Freezing (pg 113)Boiling (pg 114, 1st paragraph)Condensation (pg 114, 2nd paragraph)Evaporation (pg 115) – The process of changing a

liquid to a gas.

Sublimation (pg 116)

(Note in textbook)

CHANGE IN STATE OF MATTER DAILY LIFE

1) Wet clothes – when wet clothes dry in the sun, the water in the clothes evaporate.

2) Puddles of water - After a rain, there are puddles of water on the ground. When the sun come out, these puddles evaporate.

3) Ice cubes – Ice cube can be prepared by freezing water under low temperature.

4) Moth ball – Moth ball become smaller because of the process of sublimation.

5) Rainwater - Water vapours in clouds condense to form rainwater.

(Page 118-119-120- textbook)(Page 114- Science process skills)

7.4 : Application of expansion and contraction of matter

Good heat absorber

Dark and dull

surface

Bad heat absorber

White and shiny

surface

Good giving out (emits) heat

Bad giving out (emits) heat

7.5 : Absorbing and Giving Out Heat

Dark and dull

surface

White and

shiny surfac

e