chapter 2 notes!

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Chapter 2Exploring Diversity of Matter by Its Physical Properties

• How can the physical properties of materials help us determine their functions?

• How does the diversity of physical properties contribute to our daily lives?

• How can matter be classified by its physical properties?



2.1 Physical Properties of Matter

2.2 Density



At the end of this section, you should be able to answer the following questions:

How do physical properties determine

which material is used to make an object?

What are physical properties?


Lesson trigger

• The preserved mummy of King Tutankhamun was encased in an intricately carved, solid gold coffin.

• Gold can be easily beaten, moulded and engraved with complex details. Gold is also shiny and able to retain its original lustre.



• The physical properties of one material are different from that of another material.

• The physical properties of a material are qualities that can be detected by using our five senses or a measuring device.

Go to Link (Page 26)



• Materials can be classified into metals, glass, plastics, ceramics and fibres.

• Materials are classified according to their common physical properties.

• To determine if a material is suitable for making an object, we consider its physical properties.

Choosing the right material

Go to Link and Take Note (Page 27)



• In choosing the right material, we should ask some questions such as:

What purpose does this object serve?

Does this object need to

be strong?

Does the object need to

be flexible or rigid?

Should this object be able to conduct heat or electricity?

Should this object be able to withstand scratches?

Does this object need to be denser

than a specific substance?

Should this object have high or low boiling and melting points?

Go to Science Bites (Page 27)

Is the cost of this material too much for the purpose it is used for, even if it

has ideal properties?



Flexibility

Flexibility

• The flexibility of a material is its ability to:

• bend without breaking; and

• return to its original size and shape after bending.

Rubber is an example of a flexible material. Rubber is usually used in the manufacture of automobile tyres.

This flexible measuring tape is made from a type of plastic that can bend without breaking.



Hardness

• The hardness of a material is its ability to withstand scratches.

• A material can cut or scratch a material that is less hard than itself but not a material that is harder.

• Steel and ceramics are examples of hard materials.

Steel drills are used to bore holes through hard rock.




Melting point

• The melting point of a material is the temperature at which it changes in state from a solid to a liquid.

Ceramic has a very high melting point and can withstand temperatures of up to 1370°C!

Hence, ceramic tiles are used in space shuttles to provide thermal protection when the rockets are fired.

Ceramic has a very high melting point and can withstand temperatures of up to 1370°C!

Hence, ceramic tiles are used in space shuttles to provide thermal protection when the rockets are fired.


mercury

Mercury, compared to other metals, has a low melting point of –38.83 °C. Thus, it exists as a liquid at room temperature. Mercury is usually used in thermometers.

Mercury, compared to other metals, has a low melting point of –38.83 °C. Thus, it exists as a liquid at room temperature. Mercury is usually used in thermometers.

Find out what other materials have high melting points. In what ways can they be useful to us?



Boiling point

• The boiling point of a material is the temperature at which it changes in state form a liquid to a gas.

Go to Practical Book Link (Page 28)



Liquid nitrogen boils at a very low temperature of -196 oC. Objects freeze rapidly upon contact with liquid nitrogen.

Liquid nitrogen boils at a very low temperature of -196 oC. Objects freeze rapidly upon contact with liquid nitrogen.

Click here for a demonstration on how to make instant ice-cream using liquid nitrogen. Why is liquid nitrogen used to make ice cream?

Here, you can see hot liquid iron being poured into its cast. Since iron has a very high boiling point of 2750oC, it does not boil into a gas even when it glows red hot!

Here, you can see hot liquid iron being poured into its cast. Since iron has a very high boiling point of 2750oC, it does not boil into a gas even when it glows red hot!



Strength

• The strength of a material is its ability to support a heavy load without breaking or tearing.

The Golden-orb weaving spider produces dragline silk. It is stronger than steel and more elastic than nylon. It can be stretched up to four times its length without breaking!

Click here for a video of the Golden-orb weaving spider in action! Provide some examples of organisms that the Golden-orb weaving spider feeds on.



Electrical conductivity

• The electrical conductivity of a material is a measure of how readily electricity passes through it.

• Materials that allow electricity to pass through them easily are called electrical conductors.

• Materials that do not allow electricity to pass through them easily are called electrical insulators or poor electrical conductors.

electrical wire

PVC coating

Electrical wires are usually made of copper which allows electricity to pass through it easily. Polyvinyl chloride(PVC) coating on wires protects us from being electrocuted as it is an electrical insulator.

Electrical wires are usually made of copper which allows electricity to pass through it easily. Polyvinyl chloride(PVC) coating on wires protects us from being electrocuted as it is an electrical insulator.



Thermal conductivity

• The thermal conductivity or heat conductivity of a material is a measure of how readily heat passes through it.

• Materials that allow heat to pass through them easily are called heat conductors.

• Materials that do not allow heat to pass through them easily are called heat insulators or poor heat conductors.

Cooking pots and frying pans are usually made of heat conductors like metals. The handles are usually made of heat insulators like wood or plastic.

Cooking pots and frying pans are usually made of heat conductors like metals. The handles are usually made of heat insulators like wood or plastic.



Density

• The density of a material is the quantity of matter packed into a unit volume of the material.

• By comparing the densities of substances, we can predict whether one will float in the other.

Go to Workbook Link,Practical Book Link and Key Ideas (Page 29)





2.2 Density


2.2 Density

At the end of this section, you should be able to answer the following questions:

How does density affect the floating and

sinking of objects?

What is density?


• The Dead Sea is located between Israel and Jordan.

• The Dead Sea has about eight times more salt dissolved in 1 cm3 of water than other seas. It is much denser and contains a higher concentration of salt compared to other bodies of water in the world.

• The higher concentration of salt in the Dead Sea makes it much easier to float in this sea than other seas.

Lesson trigger

2.2 Density

Go to Think and Explore (Page 30)


• Let us take a fresh chicken egg for example. How do we measure the density of a fresh chicken egg?

• Density is the quantity of matter packed into a unit volume.

Density = MassVolume


• To measure the density of the egg, we need to first find its mass and volume.

2.2 Density


• Measurements are expressed in two parts — the numerical value and the unit.

21 metres

15 kilograms

The numerical value tells us how much there is of something.

The unit tells us the standard that we are comparing the value to. Measurements of different physical properties have different units.

Units of measurement

2.2 Density


• In order to establish common standards in measurement, scientists use the International System of Units, denoted by ‘SI’.

• Today, SI units are the most widely used system of units in Science.

Physical quantity SI unit Symbol

Length metre m

Mass kilogram kg

Temperature Kelvin K

Time second s

What is a feet, a pint, an ounce or a mile? Click here for a video to learn more about these older imperial units.

2.2 Density

Units of measurement


• A rod is suspended by a string tied at its centre.

• Let us see what happens when we hang two objects from the two ends of the rod.

When the rod is horizontal, we say that the two objects balance each other.

If objects A and B are switched around, they would still balance each other.

A AB B

What is it that makes the two objects balanced?


Mass

2.2 Density


• We know that something in Object A is exactly equal to something in Object B. That ‘something’ is the quantity of matter.

• The SI unit of mass is the kilogram (kg).

• Other units for mass are the gram (g), milligram (mg) and tonne (t).

• Mass is a measure of the quantity of matter in a body.

Go to Take Note (Page 32)

Mass

2.2 Density


Instruments for measuring mass

• We use balances to measure mass.

• The different types of balances are shown below.

Most four-beam pan balances can measure masses of up to 311 g.

Most triple-beam balances can measure masses of up to 610 g.

Most electronic balances can measure masses of up to 3,500 g.

2.2 Density


• The SI unit of length is the metre (m).

• Other measurements of length include:

• Length is the distance between two specified points.

thickness

depth

width

height

circumference

Length

2.2 Density



2.2 Density

Instruments for measuring length

Metre rule

• A metre rule is used to measure lengths of up to 1 m.


A soft and flexible measuring tape is often used by tailors.

2.2 Density

A retractable measuring tape is often used in construction or carpentry.


Measuring tape

• A measuring tape is used to measure lengths that are greater than 1 m or lengths that are curved.



Vernier calipers

• Vernier calipers are used to measure short lengths and diameters of objects of up to 10 cm.

• The smallest division on the vernier scale is 0.01 cm compared to 0.1 cm on the metre rule.

What does this say about vernier calipers compared

to a metre rule?

2.2 Density

• Hence, vernier calipers give a more accurate measurement than a metre rule.



Vernier calipers

2.2 Density

Outside jaws • Measure the external diameter or width of an object.

Main scale• Measures up to one decimal place.

Tail • Measures the depth of an object or hole.

Vernier scale• Measures up to two decimal places.

Inside jaws• Measure the internal diameter of an object.

Go to Practical Book Link (Page 35)


• The SI unit of mass is the cubic metre (m3).

• Other unit for mass are the cubic centimetre (cm3), litre (l) and millilitre (ml).

• Volume is the amount of space an object occupies.

Volume

How does the properties of different materials make them suitable to serve different functions? Click here for a game on building materials .

2.2 Density


Volume of liquids

• A measuring cylinder can be used to measure the volume of liquids.

• In narrow glass measuring cylinders, the liquid level is curved into a shaped called the meniscus from which the reading is taken.

How do we take a reading from the

meniscus?

Volume

2.2 Density


Volume of liquids

For most liquids such as water, the meniscus curves down towards the centre.

To avoid parallax error, place your eyes at the same level as the bottom of the meniscus.



Volume

2.2 Density


Volume of regular solids

l

ll

CubeVolume = l × l × l

CuboidVolume = l × b × h

b

l

h

Key: l = lengthb = breadthh = height r = radiusπ = 3.142

We can measure the volume of regularly shaped solids by using formulae involving measurements of different lengths.

Volume

2.2 Density


Volume of regular solids

Cone

r

r

h

Cylinder

h

r

Volume

2.2 Density

Volume =

Sphere

Volume =Volume =


Volume of irregular solids

• The volume of an irregular solid can be measured by the displacement of a liquid.

• In this method, we use a measuring cylinder to measure the volume of an irregular solid.

• The volume of the displaced liquid is equal to the volume of the solid.

Volume

2.2 Density


• Density, not weight, determines whether objects sink or float.

• When an object is placed in a medium, it will sink if is denser than the medium.

• However, if the object is less dense than the medium, it will float.



Floating and sinking2.2 Density

wooden block

paper clip

water


Your body is denser than water. So you will normally sink in water.

Your body is denser than water. So you will normally sink in water.

However, in the Dead Sea, most people will be able to float easily as their bodies are less dense than the seawater. This is because the water in the Dead Sea has a high density of about 1.24 kg/l due to its unusually high salt concentration.

However, in the Dead Sea, most people will be able to float easily as their bodies are less dense than the seawater. This is because the water in the Dead Sea has a high density of about 1.24 kg/l due to its unusually high salt concentration.

So what can you do to ensure you will

float in water?

Floating and sinking

2.2 Density


Substance Density (g/cm3) Substance Density (g/cm3)

Teak wood 0.85 Aluminium 2.7

Ice 0.92 Diamond 3.5

Cooking oil 0.95 Lead 11.3

Water 1.00 Mercury 13.6

Rubber 1.52 Gold 19.3

Sand 1.6 Platinum 21.4

• By comparing the densities of common substances in the table below, you can predict which will sink or float when the substances are combined.

Go to Workbook Link andPractical Book Link (Page 38)

Floating and sinking

2.2 Density


Materials

Plastics Ceramics Fibres

are classified into

Metals Glass

determine the choice of materials in the production of

everyday objects

(cont’d on next slide)

such as

Flexibility

Hardness

Melting point

Boiling point

Strength

Electrical conductivity

Thermal conductivity

Density

(cont’d on next slide)

Map It

Physical properties

differ by their


Length Volume Mass

can beMeasured

measured by measured by measured by

Metre rule, measuring tape, vernier calipers

Measuring cylinder and/or displacement

can

Beam balance, electronic balance

Density =

(SI unit: g/cm3)

is calculated by the formula

MassVolume

Whether a substance

floats or sinks

determines

Map It


Go to Get it Right (Page 40)

Go to Let’s Review (pages 40- 41)

Go to Science Today (Page 42)

Click here for a mini quiz on the physical properties of materials.

Chapter 2 Exploring Diversity of Matter by Its Physical Properties


• Polyurethanes are organic materials that expand to fill up a given space when mixed with certain substances. They have excellent insulating properties.

• Hence, they are typically used in spray foam insulation to protect buildings against heat loss or heat gain.

• Spray foam insulation saves energy costs as the need for heating systems or air-conditioning is reduced.

polyurethane spray foam

Click here for more info on building insulation.How does buildings lose heat and what are some ways to reduce heat loss?

Find Out More!

chapter 2 notes!

Documents

fresh chicken

practical

flexible measuring

measuring

melting point

boiling point

electrical

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