Effects of Heat EnergyPages 118 to 125

Think, pair, share Why you think that

there are gaps in between the railway track?

Objectives 1 State the forces of expansion and contraction in

solids State examples and applications of heat energy in

solids

Heat Energy Objects heated – Size increase, EXPANSION Objects cooled – Size decrease, CONTRACTION Expansion and contraction occurs in all 3 states of

matter – solid, liquid and gas

Effect of heat energy - Solid Expansion and contraction of solids are

so small Different metals expand and contract at

different times and by different amounts Examples

Railway tracks will expand on hot days if no gap very dangerous, train can derail and endanger passengers

Bridges have fitted rollers to allow for expansion and contraction, allow bridge to slide over them smoothly when expanded

Overhead cables and telephone lines expand during hot and contract and become taut on cold days. Hang loosely.

Effect of heat energy - Solid Examples

Concrete surfaces such as road and paths expand when heated, small gaps found every few meters in the concrete roads and paths

Pipes carrying water or steam are looped at intervals to allow for expansion. If not the pipes will burst

Applications of heat energy - Solid Rivets are used to join two steel

plates together. Hot rivet is driven through the hole in the plates. One end of the rivet is hammered to form a new rivet head. When cool, the rivet will contract and held the two plates tightly together

http://www.bbc.co.uk/schools/ks3bitesize/science/chemistry/particle_model_5.shtml

Applications of heat energy - Solid Bimetallic strips made up of two different metal, steel/iron

and brass Hotter bend downwards, colder bend upwards Both metals expand and contract by different amounts. Brass expands and contracts more than steel

Applications of heat energy - Solid Bimetallic strips is use in

thermostats in refrigerators, ovens, irons and heaters

Regulate the temperature of these appliances

It is also used in fire alarms, when the strip gets hot, it bends and completes an electrical circuit. A bell in the circuit rings to warn of a fire

Review Questions Do Checkpoint Question 1 pg 120 Do Inquiry time Question 1 pg 121 Do Checkpoint Question 2 pg 122

Objectives 2 State the forces of expansion and contraction in

liquids State examples and applications of heat energy in

liquids

Effect of heat energy - Liquid Almost all liquids

expand when heated and contract when cooled

Drink factories need to allow space when filling up their bottles or cans

No allowance will caused the bottles or cans to burst

Application of heat energy - Liquid Liquid in glass thermometer Mercury or alcohol

thermometers Thermometer is filled with

mercury or alcohol in the bulb

When in contact with cold substances mercury/alcohol will contract and the mercury/alcohol thread will drop

When in contact with hot substances mercury/alcohol will expand and causing the mercury/alcohol thread to rise

Unique quality of water Water expand when it is

being cooled from 4˚C to 0˚C

Starts to contract when heated from 0˚C to 4˚C

It reaches its minimum volume and maximum density at 4˚C

Objectives 3 State the forces of expansion and contraction in gases State examples and applications of heat energy in

gases

Effect of heat energy - Gases Gases expand when

heated and contract when cooled

Gases expand and contract much more than solids and liquids of the same volume for the same change in temperature

Effect of heat energy - Gases Example, we should

not pump car tyres to the maximum pressure on hot days – may burst

Application of heat energy - Gases Hot balloon uses the

expansion of gases Filled with heated air As volume of air increases

(expansion), the density of air decreases

Warm air less dense this it rises and carries the balloon upwards

Application of heat energy - Gases Baking bread or cake,

baking powder is added Carbon dioxide gas is

released from the baking powder expands

Causing the dough to rise

Review Questions Do Checkpoint Question 2 pg 120 Do Checkpoint Question 3 pg 122

Objectives 4 Explain using a particulate model for expansion and

contraction

Expansion and Contraction When substances expand

or contract, the particles stay the same size

Only the spaces between the particles changes

The particles in the solid vibrate more when it is heated thus take up more room - EXPANSION

Similar to liquid and gases when heated

Expansion and Contraction The particles in solid will

vibrate less when it is cold thus take up less space – CONTRACTION

Similar to liquid and gases when cooled

Review Questions (page 125) Do it now!