science form1 chapter 7
TRANSCRIPT
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