effects of heat energy
DESCRIPTION
TRANSCRIPT
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!