What is HEAT?
Form of energy and measured in JOULES
Particles move about more and take up more room if heated – this is why things expand if heated
It is also why substances change from: solids liquids gases when heated
1. HEAT ENERGYHEAT ENERGY
What is HEAT?
Form of energy and measured in
JOULES
Particles move about more and take up
more room if heated – this is why things
expand if heated
It is also why substances change from:
solids liquids gases
when heated
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2. Heat and TemperatureHeat and Temperature
The temperature of an object tells us how
HOT it is
Measured in degrees Celsius - °C
It is NOT the same as heat energy although
the two quantities are related.
e.g. a beaker of water at 60 °C is hotter
than a bath of water at 40 °C BUT the
bath contains more joules of heat energy
3. Heating and CoolingHeating and Cooling
If an object has become hotter,
it means that it has gained heat energy.
If an object cools down, it means it has
lost energy
4. Heating and Cooling cont…Heating and Cooling cont…
Heat energy always moves from:
HOT object COOLER object
e.g.Cup of water at 20 °C in a room at 30°C -
gains heat energy and heats up – its temperature
rises
Cup of water at 20 °C in a room at 10°C
loses heat energy and cools down – its
temperature will fall.
6. Temperature ScalesTemperature Scales
Three different ones get used
Fahrenheit- the one we use
Celsius- metric standard
Kelvin- starts at absolute zero but
same degree size as Celsius
7. HistoryHistory
Daniel Gabriel Fahrenheit
Chose two reference points
Coldest (mixture of salt, water, ice) 0F
Body temperature 96 (slightly in error = 98.6)
First to utilize mercury
Anders Celius
His two reference points: boiling point of water and
the freezing point of water
Lord Kelvin
Zero point is absolute zero (-273.15o
C) and 0o
C is
273.15 K
9. Sample ProblemsSample Problems
1.Water freezes at 32°F, what is this in
Celsius?
2. Water boils at 100°C. What is this in
Fahrenheit? In Kelvin?
3. Methanol boils at 75°C, what is this in
Fahrenheit?, in Kelvin?
11. ConductionConduction
Heat is transferred through a material by
being passed from one particle to the next
Particles at the warm end move faster and
this then causes the next particles to move
faster and so on.
In this way heat in an object travels from:
the HOT end the cold end
12. Conduction cont…Conduction cont…
Occurs by the particles hitting each other
and so energy is transferred.
Can happen in solids, liquids and gases,
Happens best in solids-particles very close
together
Conduction does not occur very quickly in
liquids or gases
13. ConductorsConductors
Materials that conduct heat quickly are
called conductors
All metals are good conductors of heat
Copper is a very good conductor of heat
Pans for cooking are usually made with a
copper or aluminium bottom and plastic
handles
14. Insulators/poor conductorsInsulators/poor conductors
Materials that conduct heat slowly or poorly are
called insulators
Glass, wood, plastic and rubber are poor
conductors (good insulators)
Nearly all liquids including water are poor
conductors (good insulators)
Gases, including air are poor conductors,e.g., wool
feels warm because it traps a lot of air
A fridge has insulation material round it to keep it
cold – reduces amount of heat conducted to inside
from the warmer room
15. ConvectionConvection
Takes place in material where particles can
move around inside the material, i.e. liquid or
gas
The heat is carried by the particles themselves
moving Convection
currents
Occur because an area with warm particles
expands and becomes less dense than the
cooler areas nearby. The warm area rises.
Cooler particles fall into the space left by the
warm particles and convection current is set up
16. Convection CurrentsConvection Currents
Hot liquids and gases expand and rise
while the cooler liquid or gas falls
1. Hot air rises
2. Goes across
3. Then down
4. And across
17. Convection cont…Convection cont…
The sun can cause large convection
currents - WINDS
During daytime the land warms up more
than the sea. The warm air rises over the
land and cool air falls over the sea. So we
feel a sea breeze.
Rising convection currents can be uses by
glider pilots to keep their planes in the air
and by birds to stay aloft.
18. RadiationRadiation
Transfer of heat directly form the source to the
object by a wave, travelling as rays.
Heat radiation is also known as
All objects that are hotter than their surroundings
give out heat as infra-red radiation
Heat transfer by radiation does not need particles
to occur and is the only way energy can be
transferred across empty space
INFRA-RED
RADIATION
19. EmittersEmitters
Hotter objects emit (give out) heat
Different surfaces emit heat at different speeds
A dull black surfaces loses energy more
quickly – it is a good radiator
A bright shiny or white surface is a poor
radiator
Marathon runners need to keep warm at the end
of races, covering in shiny blankets reduces
radiation and therefore heat loss.
21. AbsorbersAbsorbers
Cooler objects absorb (take in) heat
Substances absorb heat at different speeds
Dull, black surfaces absorb heat quickly
Bright, shiny surfaces absorb heat slowly
In hot countries, people wear bright white
clothes and paint their houses white to reduce
absorption of energy from the sun.
Petrol storage tanks sprayed silver to reflect
sun’s rays