P4 1st Term Ch1 Slides

Properties of Water

水的特性

New General Studies New Curriculum P4.2

 About 3.5% of all

Earth’s water is fresh
water ), such as
water falling from the
skies and moving into
streams, rivers, lakes,
and groundwater

The Earth is a watery place!

 About 71% of the

Earth’s surface is
water-covered.

 The oceans hold

about 96.5%of all
Earth's water and is
saline water鹽水.

Water is never still ---

The Water Cycle

Learning objectives

1.What are the properties of water?

2.What are the features of the surface tension of

water?

3.Does water exert pressure?

4.What are the three states of water?

5.How does water change from one state to another?

6.What factors affect the evaporation rate of water?

Sense organs:

Properties of Water:

It (has / has no) colour.

It ( has / has no ) smell.

It ( has / has no ) taste.

Properties of Water

Prediction

Water flows (upwards / downwards).

Properties of Water

Water flows (upwards / downwards).

(due to gravity)

Think about it!

Which areas in Macao are more likely to flood during heavy rains? Why?
Explain based on the properties of water.

The Inner Habour

Toi San

San Kio

Flooding in low-relief areas

As water flows

downwards, these

low-relief areas are

more likely to flood

during heavy rain.

Properties of Water

Prediction

Some things / Nothing can float on water.

Some things / Nothing can float on water.

Does shape affect floating?

Do you think the shapes of objects affect whether
they can float on water? Why or why not?

Ball shape

Bowl shape

Does shape affect floating?

Materials:

Water

Two pieces of plasticine with

the same size and weight

A transparent

water tank

Procedures:

Step 1: Fill the tank with water.

Step 2: Shape the two pieces of

plasticine into a ball shape and a bowl

shape respectively.

Step 3: Put the two pieces of

plasticine on the water and observe

what happens.

The ball-shaped plasticine ( floats / sinks ).

Results

The bowl-shaped plasticine ( floats / sinks ).

The two pieces of plasticine are (the same / different) in weight.

Their shapes are (the same / different) .

The ( ) of an object affect whether it can float on water.

shape

Water does not have colour, (

) or ( ).

It flows ( ) and (

)can float on it.

smell

taste

downwards

some things

Properties of Water

Make a guess!

Will it spill out if we slowly
add water drop by drop?

What will happen if we place a
paper clip on the water surface?

The paper clip sinks / floats.

Why does the paper clip float on

the water?

An internal force pulls the

surface of water to make it act

like a stretched film

Surface
tension
表面張力

The surface tension of water

supports the paper clip, making it

stay on the water surface

Surface tension

Surface tension - An internal force
that pulls the surface of water to
make it act like a stretched film

Adding detergent into the water

After adding a few drops of detergent,

the surface tension of water

(increases / decreases ).

The water is unable to support the

weight of the paper clips, so the paper

clip ( sinks / floats ).

Everyday examples of surface tension

Dew on leaves

Water strider

Drips from taps

Why are drops spherical?

Surface tension of water (can

/ cannot) make some

objects, such as paper clips,

stay on water surface.

Surface Tension表面張力

What do you feel? Why?

The glove is (loose / tight)

against the skin in water

because of (surface tension

/ water pressure).

Water pressure水壓

The force that water produces when it
presses against an area.

Relationship between water pressure

and the depth of water

Hypothesis

Water pressure (increases / decreases) as the
depth of water increases.

Experiment of water pressure

Relationship between water pressure

and the depth of water

Results

The water from hole ( ) reached
the least far from the bottle.

The water from hole ( ) reached
the farthest from the bottle.

Analysis

The farther the water reached, the (lower / higher)
the water pressure.

Water pressure (increases

/ decreases) as the depth

of water increases.

Water pressure

States of Water

Three states of water

Solid

Has a fixed shape

Cannot flow

Liquid

Does not have a fixed shape

Can flow

Gas

Does not have a fixed shape

Can flow

We cannot see water vapour.
The white smoke we see is the
water droplets condense from
water vapour.

Invisible water vapour from a hot spring

Invisible water vapour from a volcano

1

2

Gas – water vapour

Fog

Is fog gas?

(Fog is produced when water vapour is cooled and condensed
into water droplets in the air. Therefore, fog is liquid.)

Steam

Is steam gas?

(Water vapour is gas. However, steam
is produced when water vapour is
cooled and condensed into water
droplets in the air. Therefore, steam is
liquid when visible.)

Steam may or may not be considered as gas!
Ranges from pure liquid(0) *visible* to pure vapour(1) *invisible* !

Water Vapour is always considered as gas!

The uses of water in different states

Solid

Liquid

Gas

Keeping food fresh

Drinking
Cooking

Liquid
Hydropower
generation

Irrigation
Manufacturing

Surfing

Solid

Ice hockey

Ice skating

Snowboarding

Gas
Sauna

Sterilisation

Ironing

The three states of water

are ( ), ( ) and

( ).

Three states of water

Changes of state of water

melting

evaporation

freezing

condensation

Water changes from one state to

another as temperature rises or drops.

The changes of state of water

are reversible!

Changes of states of

water in daily life

The child draws on the ground using water. After a
while, the picture changes. What change of state of

water is it related to?

The water on the ground evaporates into water vapour,

so the picture on the ground slowly disappears.

evaporation

What change of state of water is the

following phenomenon related to?

It’s so tasty!

1

There are fewer ice
cubes. The taste
becomes weaker. Its
colour also becomes
lighter.

2

Ice melts at room temperature. There are more water in the drink so it tastes weaker.

melting

When people cook, their glasses fog up. What change

of state of water is it related to?

When the hot water vapour comes into contact with the cold lenses, it

condenses and turns into small water droplets.

condensation

Fruit juice turns into an ice lolly in the freezer.
What change of state of water is it related to?

Water in the fruit juice
freezes into ice, turning

juice into an ice lolly.

freezing

Water droplets appear on the lid of a thermal mug.

What change of state of water is it related to?

1. Water in the thermal mug evaporates
into water vapour.

2. The water vapour condenses into water
droplets when it comes into contact with the
cooler lid.

evaporation

condensation

Water droplets appear on a cold soft drink

can. What change of state of water is it

related to?

Water vapour in the air condenses into water droplets

when it is cooled by the surface of the cold can.

condensation

How do people get salt

from sea water?

Conclusion

What factors affect the

evaporation rate of water?

Which clothes is hung in a place with a higher temperature?

High temperature

Water molecules gain more energy at higher temperatures, so they
can escape from the water surface more easily, thus increasing the
evaporation rate.

What factors affect the

evaporation rate of water?

Which clothes is hung in a place with better ventilation?

Good Ventilation

In place with good ventilation, wind blows away water molecules
from the water surface, thus speeding up evaporation.

What factors affect the

evaporation rate of water?

Which method of hanging clothes increases the surface area of water exposing to the air?

Large Surface Area

The larger the surface area of water exposing to the air, the larger
the area for water molecules to escape from the water surface,
resulting in higher evaporation rate.

Why does ice
float on water?

Water has an unusual property. When water is cooled, its volume decreases till it reaches 4 °C.
When it is cooled below this temperature, its volume increases till it reaches 0 °C.
At 0°C, liquid water changes into ice.
Ice floats on liquid water because it expanded and is less dense than liquid water.

Water reaches 0 °C
and turned to ice

Water cooling below
4°C

Water cooling above
4°C

A piece of ice is placed in a glass of water.
Which picture best shows the position of the
ice in the water?

A closed glass bottle filled with water was left in the freezer overnight.
In the morning the glass was found broken!
Why did freezing the water cause the bottle to break?

The water

expanded

when it’s below 4 °C and there was

not enough room

in the bottle for the water to freeze so it

broke.