Chapter 2: Exploring Diversity of Matter by its Physical Properties (Summary Sheet)

Part A · Physical Properties

1 What a Physical Property Is

A physical property is anything about a material that you can observe or measure without changing it into a new substance.
Two kinds: the ones you observe (colour, state, whether it is transparent, whether it feels cold) and the ones you measure and give a number to (conductivity, melting point, density, hardness).
Only the measured ones can be compared properly, because a number and a unit can be checked; “quite hard” cannot.
Properties are what let you decide which material suits a job — the choice is made from data, not from habit.

2 The Properties You Must Know

Property	What it tells you	How it is measured
Electrical conductivity	How easily electric current flows through the material	Put the material in a circuit with a cell and a lamp or buzzer — good conductors light it, insulators do not
Thermal conductivity	How easily thermal energy flows through the material	Heat one end of a rod and watch how fast wax or butter melts along it
Melting point	The temperature at which the material changes from solid to liquid	Heat it slowly with a thermometer in it, in °C
Boiling point	The temperature at which the material changes from liquid to gas	Heat it and read the steady temperature while it boils, in °C
Strength	How large a force the material can take before it breaks, stretches or tears	Hang increasing masses from it until it gives way
Hardness	How well the material resists being scratched	Scratch one material with another; the Mohs scale goes from talc (1) to diamond (10)
Flexibility	How easily the material bends without breaking	Bend it and see whether it returns to its shape or snaps
Density	How much mass is packed into each unit of volume	Measure the mass and the volume, then divide

The same material can be strong and hard, or strong but flexible: steel is strong and hard, rubber is strong and flexible. Never treat the two as the same property.

3 Mass, Volume and Density

Mass is the amount of matter in an object, in g or kg. It does not change if the object is moved.
Volume is the amount of space the object occupies, in cm³ or m³ (1 cm³ = 1 mL).
Mass and volume together decide density: the same volume of two materials with different masses means the heavier one is denser.

Two blocks, same size	Mass	What that means
Aluminium block	54 g	Lower density — matter is packed less tightly
Iron block	158 g	Higher density — matter is packed more tightly

Part B · Measuring Length, Mass and Volume

4 Measuring Length

Choose the instrument that fits the object — a longer instrument on a short object loses precision.

Instrument	Use it for	Smallest division
Measuring tape	Long or curved lengths — a table top, the waist of a person	1 mm
Metre rule	Straight lengths up to 1 m — a book, a block	1 mm
Digital calipers	Small objects, and the internal or external diameter of a tube or rod	0.01 mm (0.1 mm on the scale)

Start from the zero mark, not from the end of the rule — the end is often worn or has a gap.
Read with your eye directly above the mark; looking from one side gives a parallax error and a reading that is too high or too low.
Always write the reading with its unit, and to the smallest division the instrument shows.

5 Measuring the Volume of a Liquid

A measuring cylinder is used for the volume of a liquid. Pick one whose capacity is just above the volume you expect, so the divisions are as fine as possible.
Stand it on a flat surface, and keep your eye level with the liquid surface.
The curved surface of the liquid is the meniscus, caused by the liquid sticking to the glass.

Liquid	Where to read
Water and most liquids	The meniscus curves up at the sides; read the bottom of the curve, at eye level
Mercury	The meniscus curves down at the sides; read the top of the curve

6 Volume of Irregular Solids: Displacement

A stone has no length, breadth and height to multiply, so its volume is found by the volume of water it displaces — an object pushes aside its own volume of water.

Method	Steps
Measuring cylinder	Part-fill with water and note the level (50 mL). Lower the object in, fully covered, with no water splashing out. Note the new level (58 mL). Volume = 58 − 50 = 8 cm³
Displacement can	Fill until water just reaches the spout. Submerge the object and collect the water that overflows. The volume collected = the volume of the object
Sinker method (floating objects)	Objects that float, such as cork, will not sink on their own. Tie on a sinker that is denser than water: read the level with the sinker alone (58 mL), then with both submerged (66 mL). Volume = 66 − 58 = 8 cm³

Reading the result: the answer is a difference, so both levels must come from the same cylinder in the same position, and the object must be fully under the water before the second reading is taken.

7 Measuring Mass

An electronic balance is used for mass. It should read zero before anything is placed on it.
Tare sets the reading back to zero with a container already on the pan, so the balance then shows only the mass of what is poured in.
Read the mass with its unit — g for small objects, kg for larger ones — and never move the balance while weighing.

8 Estimate First, Measure Second

Estimate the length, mass or volume before measuring: a sensible estimate is a check on a reading that came out wrong by a factor of ten.
Use the unit that fits the size of the thing: mm for a nail, cm for a pencil, m for a room; g for a coin, kg for a bag of rice; mL for a cup, L for a bottle.
Every measurement carries a small uncertainty, so a recorded value states the unit and the divisions the instrument actually shows.

Part C · Density, Sinking and Floating

9 Calculating Density

Density = mass ÷ volume — the mass of each unit of volume of the material.
Units: g/cm³ when mass is in g and volume in cm³; kg/m³ when mass is in kg and volume in m³. 1 g/cm³ = 1000 kg/m³.
The units must follow the measurements given — a mass in kg with a volume in cm³ has to be changed to match before dividing.

Find	How to rearrange it	Worked line
Density	density = mass ÷ volume	A block of 81 g and 30 cm³ → 81 ÷ 30 = 2.7 g/cm³
Mass	mass = density × volume	2.7 g/cm³ × 30 cm³ = 81 g
Volume	volume = mass ÷ density	81 g ÷ 2.7 g/cm³ = 30 cm³

Density is a property of the material: cut a block of iron in half and both halves keep the same density, because mass and volume fall together.

10 Sinking and Floating

Predict it by comparing the density of the object with the density of the surrounding medium — water, salt water or air. Nothing else decides it.

Comparison	What happens
Object denser than the medium	Sinks — a piece of iron in water (7.9 g/cm³ against 1.0 g/cm³)
Object less dense than the medium	Floats — a block of wood in water (0.65 g/cm³ against 1.0 g/cm³)
Object the same density as the medium	Stays where it is put, neither rising nor sinking

The denser the medium, the higher the object floats in it: wood floats in both methylated spirit (0.79 g/cm³) and glycerine (1.26 g/cm³), but sits higher in glycerine.
A ship floats because its steel hull is shaped to enclose air, so the whole ship averages less than the density of water. Load it too heavily and the average rises above the water's density, so it sinks — which is why a hull carries load lines.
An object that sinks still displaces water: the level rises, which is exactly what the displacement method measures.

Part D · Classifying Materials and Choosing Between Them

11 One Group of Objects, Many Ways to Classify

Classifying means sorting objects into groups that share a property. There is no single correct grouping — the same collection can be sorted several ways.
State the criterion you used, and justify it: the grouping is only useful if the property matters for the question being asked.

Criterion	Groups	When it is useful
Material	Metal, glass, plastic, ceramic, fibre	Choosing what an object should be made of
Density	Floats in water / sinks in water	Predicting floating, or checking whether a metal is pure
Hardness	Can be scratched by a fingernail / by a coin / only by diamond	Anything that must resist wear, such as a floor or a tool
Electrical conductivity	Conductors, insulators	Deciding the wiring and the covering around it
Thermal conductivity	Conductors, insulators	Deciding the pan and the handle on it
Strength and flexibility	Rigid or bendy; weak or strong	Anything that must carry a load or be folded

12 Choosing a Material by Its Properties

To evaluate whether a material suits a job, name the property the job needs and compare the materials on data, not on appearance.

Object	Material	Which property earns it the place
Cooking pot	Metal	Good thermal conductor, so heat reaches the food, and a high melting point so it keeps its shape on the stove
Pan handle	Plastic or wood	Poor thermal conductor — it stays cool enough to hold
Electrical cable	Copper inside, plastic outside	Copper is a good electrical conductor; the plastic is an insulator, so the current stays in the wire
Window	Glass	Transparent, hard, rigid and able to keep out rain
Carrying bag	Fibre or plastic	Flexible and strong for its mass, and low density, so it is light to carry
Drinking cup	Ceramic or glass	Hard, rigid, easy to clean, and does not react with the drink
Wire fence	Metal	Strength and flexibility: it is pulled tight and still bends rather than snapping

Answering an “evaluate” question: name the property, say why the job needs it, then compare with one other material that would fail — a property with no link to the job earns no mark. Plastic is a poor conductor of heat, so it makes a handle that can be held, whereas a metal handle would conduct heat from the pot and burn the hand.

13 Using Materials Sustainably

Material	Where it comes from	What it is chosen for
Metals	Found in the ground, as pure metal (gold) or as an ore (iron)	Conducting, strength, high melting point — pots, cables, frames
Glass	Made by heating sand, soda ash and limestone	Transparency and hardness — windows, bottles, screens
Plastics	Made from petroleum	Light, flexible, cheap, insulating — bags, bottles, wire covering
Ceramics	Made from clay	Hardness and heat resistance — cups, tiles, ovenware
Fibres	Natural (cotton) or made (nylon, polyester)	Flexible and strong, low density — clothing, bags, ropes

Some of these materials take millions of years to replace, so the choice of an object is also a choice about resources.
Reducing the use of non-sustainable materials means finding another material with similar properties: a metal straw or a fibre bag does the same job as the single-use plastic one, so less plastic is made and thrown away.
Reusing an object, or choosing one made of a material that can be recycled, cuts the amount of new material that has to be taken from the ground.
Before saying a substitution is better, check it keeps the property the job needs — glass keeps a drink in better than paper does, but it breaks.

Part E · Exam Tips

14 Exam Tips: What Each Syllabus Pointer Asks For

The pointer	What earns the mark
Describe physical properties that can be observed or measured	Name the property and state how it is found — electrical conductivity, thermal conductivity, melting point, boiling point, strength, hardness, flexibility and density. Give the unit where the property has one
Show an understanding of how mass and volume affect density	Say that density is mass ÷ volume: the same volume with more mass is denser, and the same mass squeezed into less volume is denser
Classify common everyday objects, and recognise many ways of classifying	State the criterion first, then the groups; say that the same objects could be sorted by another property too
Evaluate the usage of materials using data of their physical properties	Property → why the job needs it → compare with a material that would fail. Use the numbers given (density, melting point) rather than “it looks suitable”
Communicate findings on classification and justify reasons	Name each group, give the property the group shares, and give one reason per grouping
Estimate length, mass and volume	Give a sensible estimate with a unit before measuring, and use it to check the reading
Measure length, mass and volume accurately, including liquids and solids	Name the instrument — measuring tape, metre rule, digital calipers, measuring cylinder, electronic balance — and state the reading with its unit, at eye level, from the zero mark or the meniscus
Apply volume displacement to derive the volume of irregular objects	Give volume = final level − initial level, with both readings from the same vessel; mention the sinker if the object floats
Predict whether an object sinks or floats by comparing densities	Compare the object’s density with the density of the surrounding medium and state the outcome; if the medium changes, say what happens to the floating height
Calculate density and use the appropriate unit	density = mass ÷ volume, with the unit g/cm³ or kg/m³ that matches the measurements given
Make informed choices on the sustainable use of materials for household products	Name the material (fibre, plastic, ceramic, metal or glass), the property that suits the job, and one effect of choosing it — reused, recycled, or replaced by a material with similar properties
Appreciate how alternative materials reduce environmental impact	Say that the substitute keeps the same property while using less of a non-sustainable material