7. ⢠Heat can be transferred by anything which is matter
⢠And that includes air
⢠Liquid
⢠And solids
8. Conductors and insulators
1. Conductors allow energy to flow through
2. Insulators block energy from flowing through
3. All matter can be conductor or insulator of heat.
Including air and water.
9. 1. Anything that allows the transfer of energy is a
conductor.
2. Anything that blocks the transfer of energy is a
insulator. It holds the heat. Or it reflects the heat.
Conductors and insulators work for:
1. Heat
2. Electricity
3. sound
Good conductor
of heat
Poor conductor
of heat
metals Air
Plastic
Glass
Rubber
10.
11.
12. ⢠Wool jackets have air pockets and the trapped air traps
heat as it is a poor conductor of heat
⢠A frying pan is made of metal which is a good conductor
of heat so it heats up food fast
⢠The handle is made of a poor conductor of heat so you
wont get burnt
13. Concepts:
1. Heat always travels from hotter to colder
2. Heat wants to be distributed evenly
3. Heat transfer acts on two partners:
4. means the hotter object gets cooler and the cooler
object gets hotter
5. Heat can be transferred by solids, liquids and gasses
6. Heat can be transferred well by conductors, poorly
by insulators
18. What is the meaning of no definite volume?
Can be compressed
⢠No definite volume:
⢠Volume of gas equals volume of container
⢠Compressed syringe, volume of gas = Volume of syringe
⢠Same for pumping tire.
19. What is the meaning of no definite volume?
No definite volume
Volume of gas equals volume of container
â expands to fills up the volume of the container
20. What is the meaning of no definite shape?
No definite shape:
Shape of gas/ gas of liquid follows shape of container
21. Plasticine is a solid so it has definite shape.
But its shape can be changed as it can be moulded
32. ⢠At melting point,
⢠The solid starts to melt into liquid
⢠any increase in heat energy in the system goes into turning the
substance from solid to liquid.
⢠The temperature remains the same.
⢠There is a mixture of solid and liquid, until melting has completed
⢠only when all the substance is liquid, then the temperature starts
to rise
⢠The same applies to boiling temperature.
33. ⢠Temperature of Melting Point EQUALS temperature of
Freezing Point
⢠Temperature of Boiling Point EQUALS temperature of
Condensation Point
⢠Add heat and it will tip to melting
⢠Remove heat and it will tip to
freezing
34. Melting point
⢠Tipping point where the
substance starts to become
solid to liquid
Boiling point
⢠Point where the substance
starts to become liquid to gas
In terms of temperature,
⢠Temperature of Melting point =
temperature of freezing point
⢠Temperature of boiling point =
temperature condensation
temperature
35. ⢠At the 100 degrees Celsius, water
starts to boil
⢠Even if you continue heating, the
water stays at 100 degrees
Celsius
⢠All the heat goes into changing
water from liquid to gas
⢠Until all the water has been
turned to gas
⢠Same for melting
36. ⢠Why do bubbles form when boiling?
⢠When boiling, heat is spread throughout the
water
⢠There will be points in water where water starts
to become water vapor
⢠As boiling continues, more water vapour forms
in these points and increases the pressure and
volume of the bubbles
⢠As the bubbles get bigger they contain more air
(vapour) which makes them float to the surface
of the water
37. ⢠How do you change the boiling point of water?
⢠You add salt, which is a substance with boiling point higher
than 100 degrees Celsius â the new boiling point is the average
of the two substances boiling point
⢠You increase pressure, so the gasses are forced to compress to
liquid for the same temperature â affects the in-definite
volume property of gasses
⢠Application: pressure cooker: higher temperature can be
achieved so the food cooks faster
38. How to change the melting/freezing point of water?
Same. Add salt or other substance with melting/freezing
point greater than zero degree Celsius
Application:
Add salt to road, prevent it from freezing during winter
40. ⢠Although evaporation and boiling
⢠Both involve same change in state of water
⢠From liquid to gas,
⢠They are very differentâŚ.
⢠Evaporation happens at the surface of the
liquid
⢠It does not require heating
⢠It does not happen only at boiling point
41.
42.
43.
44.
45. Water can exist as liquid or gas between 0 to 100 degrees
Because evaporation happens in between 0 to 100 degrees
You donât need to boil water to produce water vapour which is
a gas.
What is the difference between water vapour and steam?
46. Factors affecting rate of evaporation
1. Temperature
2. Surface area
3. Wind
4. humidity
47. Temperature
Higher temperature makes the
water molecules vibrate more
become gas
Humidity
Humidity measures how packed is
the air with water vapour
Too packed, add more vapour,
water vapour starts condensing
Wind
More wind, more water molecules
are blown away from the surface
Surface area
More surface area, more area for
temperature and wind to evaporate
water
50. Condensation happens in two ways
1.Water vapor condenses around room temperature
depending on temperature and humidity.
2.Steam condenses at any temperature below boiling point
3.The temperature where water vapour vapour condenses is
lower than the temperature steam condenses.
51.
52. Solar stills
⢠Make use of solar energy to heat up water
⢠Salty water evaporates leaving behind salt
⢠Water vapour hits cools surface, condenses
⢠Water droplets slide down sloped ceiling
⢠Clean water is collected at the end of the slope
53.
54. Condensation happens when
1. Heat loss cause change in state (gas to liquid)
2. Hotter water vapour (or steam) meets a colder surface (or
air),
3. heat transferred to colder surface (or air),
4. water vapour (or steam) loses heat
5. and condenses into droplets formed on the colder surface.
6. Identify who are the cold partner and who are the hot
partner
55. Condensation
Must have temperature difference then will have either condensation or evaporation
Inside or outside water droplets
Inside = inside colder
Outside =outside colder
56. Summary of heat transfer and change of state
⢠When a hotter and colder object
⢠Comes into contact
⢠There is Heat transfer
⢠from hotter to colder object
⢠Hotter cool down
⢠condensation to water droplets
⢠Cooler heat up
⢠evaporation to water vapour
57. Can you have heat transfer if both objects have the same
temperature?
No.
61. precipitation collection
evaporation
condensation
Names of processes
heatscools
Gain/loss of heat
liquid
liquid
gas
liquid
Change in states
Water droplets
rain
Water vapor
Water
droplets
clouds
Names of water in different states
Ocean
Forest
rivers
Start here
End here
62. Summary:
1.The sun heats up the surface of the earth
2.Causing water from the oceans evaporate, and also transpiration
from plants
3.Forms water vapor, which rises to the atmosphere
4.In the atmosphere, water vapor cools and condenses to form
clouds
5.The water droplets in the clouds gather to form larger water
droplets
6.When the water droplets are too large, they start to fall as
precipitation back to earth
7.The water precipitated is collected by oceans, surface runoff and
some infiltrates the ground
64. ⢠Why is the water cycle so
important?
⢠You need to distribute the
water over the land.
⢠You cant have all the
water stuck in the
oceans!
65.
66. Why is clean water an important-and-limited resource?
1.We use water to grow crops, drink water, bathe, etc.
2.How does clean water get dirty (water pollution)?
3. How does clean water get used up?
4. Why is there so little of clean water?
5. why canât we drink ocean water?
67. Can you drink water from the oceans?
⢠No. you will die of too much salt (dehydrated) because sea water is
extremely salty.
Can you drink water off the floor? Can you drink water from a river where
people are bathing and defecating?
⢠No. you will get sick (and may die) because there are germs in the water.
Natural sources of clean water:
1. Mountain ice cap
2. Rivers â melted ice cap
3. Lakes (rivers flow into lakes)
4. Ground water (when rain seeps into ground)
68. Water and poorer nations
⢠There is no proper water supply system in poor nations
⢠No pipes for sewage (dirty water) and clean water
⢠People defecate into the river, use it for bathing and for
cooking
⢠Hence germs can spread through water and many people
fall ill from water borne diseases.
69. Water resources and politics
⢠Many countries depend on rivers water supply to grow
crops
⢠A river starts from mountain, has upstream and
downstream
⢠If the river is blocked upstream, water supply is cut
downstream
⢠May be due to building hydroelectric dams
70. Water pollution can occur in developed countries
1. Factories pollute the air â the polluted air produces acid
rain.
⢠Acid rain spoils buildings and falls back into water
resources like rivers
2. Factories pollute the water by dumping chemical waste
directly into rivers.
⢠Water becomes un-usable.
71. Reduce, reuse, recycle
1. âReduceâ
⢠Showering vs bathtub.
⢠Not letting the tap run.
2. âRecycleâ
⢠Newater
3. âReuseâ
⢠Using water from washing rice to water plants
72. Singaporeâs (clean) water resources:
1. Water catchment areas - reservoirs
2. Buy water from Malaysia
⢠Reservoirs are dependent on rainfall.
3. Newater
⢠Newater means we can turn dirty (un-usuable) water (which
is plenty) into clean, usuable water.
⢠It does not depend on rainfall.
⢠Singapore has used Newater to help other countries solve
their water problems.
