Overview
What you’ll learn
- Describe physical properties that can be observed or measured, including electrical and thermal conductivity, melting and boiling points, strength, hardness, flexibility and density.
- Calculate density using density = mass ÷ volume, with units g/cm³ or kg/m³.
- Predict whether an object will sink or float by comparing its density with the density of the surrounding medium.
- Measure length, mass and volume with suitable instruments, and find the volume of an irregular solid by displacement.
- Use data on physical properties to choose a suitable material, including a more sustainable alternative.
In 30 seconds
- 1A physical property can be observed or measured without turning the material into a new substance.
- 2Density = mass ÷ volume. Common units are g/cm³ and kg/m³. Do not multiply.
- 3An object sinks if its density is greater than the density of the liquid (or gas) around it, and floats if its density is lower.
- 4Mass is measured with an electronic balance. Volume of a liquid is read from a measuring cylinder at the bottom of the meniscus.
- 5The volume of an irregular solid is the rise in water level when it is fully submerged (displacement).
- 6Choose materials by matching properties to the job, and prefer options that reduce the use of non-sustainable materials.
Notes · 1 of 5
Physical properties you can observe or measure
A physical property describes a material without chemically changing it into something new.
Matter can be sorted in many ways. A physical property is a feature you can see or measure — colour, whether it conducts, how easily it bends — without a chemical reaction. Burning a material is not measuring a physical property: burning makes new substances.
| Property | What it means | A quick comparison |
|---|---|---|
| Electrical conductivity | Lets an electric current pass | Copper wire conducts; most plastics do not |
| Thermal conductivity | Lets heat energy pass through | A metal spoon heats up in soup; a wooden spoon does not |
| Melting point / boiling point | Temperature at which it changes state | Ice melts at 0 °C; water boils at 100 °C |
| Strength | How much force it can take before it breaks | A steel cable is strong; chalk snaps easily |
| Hardness | How well it resists scratching or denting | Diamond scratches glass; chalk does not |
| Flexibility | How easily it bends without breaking | A rubber tube bends; a ceramic tile snaps |
| Density | Mass packed into each unit of volume | A small lead sinker feels heavy for its size |
Notes · 2 of 5
Classifying materials and choosing them well
The same objects can be grouped in more than one sensible way. The useful grouping depends on the job.
There is no single correct way to classify a set of objects. You might group them by colour, by whether they conduct electricity, or by what they are made of. In an answer, state the property you used and give one example in each group.
- Metals
- Usually strong and good conductors of electricity and heat. Used for wires, pots and structures.
- Plastics
- Often light, waterproof and poor conductors. Some are flexible, some are rigid.
- Ceramics
- Hard and heat-resistant, but brittle. Poor conductors. Used for tiles and some cookware.
- Glass
- Transparent and brittle. A poor conductor of electricity. Used for windows and lenses.
- Fibres
- Thin and flexible, so they can be spun or woven into cloth and rope.
A good choice matches the property to the use: a pot base should conduct heat, but the handle should not. Where you can, choose a material that does the job with less harm to the environment — for example a reusable bottle instead of many single-use ones, when the properties still fit.
Notes · 3 of 5
Density, and why some things sink
Density tells you how much mass is packed into a given volume.
Density = mass ÷ volume. If a block has a mass of 24 g and a volume of 8 cm³, its density is 24 ÷ 8 = 3 g/cm³. The same idea in larger units uses kg/m³. Do not mix the two unit systems in one calculation.
- 1Write the formula: density = mass ÷ volume.
- 2Substitute the numbers with units: 24 g ÷ 8 cm³.
- 3Divide, and write the unit on the answer: 3 g/cm³.
Compare the object’s density with the density of whatever is around it. Water is about 1 g/cm³. If the object’s density is greater, it sinks. If it is lower, it floats. A heavy ship can float because its overall density, including the air inside the hull, is less than the density of water. Mass alone does not decide.
Notes · 4 of 5
Measuring length, mass and volume
Pick an instrument whose scale is fine enough for the size you are measuring.
| Quantity | Instrument | Unit to record |
|---|---|---|
| Length | Metre rule, measuring tape, or digital calipers | mm, cm or m |
| Mass | Electronic balance (press tare with the empty container on the pan) | g or kg |
| Volume of a liquid | Measuring cylinder, read at the bottom of the meniscus | cm³ |
| Volume of a regular block | Measure length, breadth and height, then multiply | cm³ |
| Volume of an irregular solid | Displacement in a measuring cylinder | cm³ |
Displacement: record the volume of water first, lower the object until it is fully under the water, and record the new level. Volume of the object = final level − first level. The object must not dissolve, absorb water, or trap large bubbles, and no water may splash out.
Notes · 5 of 5
Properties and more sustainable choices
Knowing properties lets you swap a material without losing the job it does.
Two materials can share a useful property and differ in how they are made or thrown away. A reusable container with similar strength and waterproofing can replace many single-use ones. That is one way the idea of reduce, reuse and recycle shows up in this chapter.
- Name the property the job needs (for example, low thermal conductivity for a handle).
- Pick the material in the data that has that property.
- If two materials both work, give a reason to prefer the one that cuts waste or lasts longer.
Revise
Key terms
The words examiners expect you to use precisely.
- Physical property
- A feature of a material that can be observed or measured without changing it into a new substance.Density, hardness and conductivity are physical properties. Burning is not.
- Density
- The mass of a substance in a given volume. Density = mass ÷ volume.Units: g/cm³ or kg/m³.
- Electrical conductivity
- How well a material lets an electric current pass through it.Metals such as copper are good electrical conductors.
- Thermal conductivity
- How well a material lets heat energy pass through it.A metal pot base conducts heat; a plastic handle does not.
- Melting point
- The temperature at which a solid becomes a liquid.
- Boiling point
- The temperature at which a liquid becomes a gas throughout the liquid.
Show 3 more key termsShow fewer key terms
- Hardness
- How well a material resists being scratched or dented.
- Flexibility
- How easily a material bends without breaking.
- Displacement
- The method of finding the volume of an irregular solid from the rise in water level when the solid is submerged.
Revise
Common mistakes
Where students most often lose marks in this chapter — and what to do instead.
Mistake: Calculating density as mass × volume.
Density is how tightly mass is packed, so you divide.
Instead: Density = mass ÷ volume.
Mistake: Saying a heavier object must sink.
Sink or float depends on density compared with the surrounding medium, not on mass alone.
Instead: It sinks when its density is greater than the density of the liquid.
Show 4 more mistakesShow fewer mistakes
Mistake: Leaving out the unit, or mixing g/cm³ with kg/m³.
A number without a unit is incomplete, and the two density units are not interchangeable without converting.
Instead: Keep mass and volume in a matching pair: grams with cm³, or kilograms with m³.
Mistake: Reading the top of the meniscus, or using a beaker for a precise volume.
The correct level is the bottom of the curve, and beaker marks are only approximate.
Instead: Use a measuring cylinder on a flat bench and read the bottom of the meniscus at eye level.
Mistake: Treating strength, hardness and flexibility as the same word.
Each describes a different behaviour.
Instead: Strength is about breaking, hardness is about scratching, flexibility is about bending.
Mistake: Forgetting an assumption in a displacement question.
The rise in level equals the object’s volume only if the object is fully submerged and no water is lost or absorbed.
Instead: State one assumption: fully submerged, does not dissolve, does not absorb water, or no bubbles trapped.
Check yourself
Quick quiz
10 questions with instant explanations. About 5 minutes.
Question 1 of 3
- Question 1: current question
- Question 2: not answered
- Question 3: not answered
Calculate density
A metal block has a mass of 54 g and a volume of 6 cm³. What is its density?
Ready for more practice on Chapter 2: Exploring Diversity of Matter by Physical Properties?
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Practise
Topical questions
Exam-style practice in three tiers, from recall to data questions.
- 5Foundation
- 5Standard
- 5Challenging
15 questions worth 49 marks, each with a model answer, mark scheme and examiner tips.
Practise topical questionsExam practice
Practice paper
A 30-mark paper set out like a school paper, with a separate mark scheme. Give yourself 40 min.
Question paper
Chapter 2 Practice Paper
30 marks · 40 min · 6 pages
10 multiple-choice questions and structured questions with answer lines. Chapter 2.
Mark scheme
PROChapter 2 Practice Paper — mark scheme
Answers · Marking points · 3 pages
Model answers with a mark for each creditworthy point — for marking at home or in class.
Where this chapter is tested
Each school sets its own scope — check your assessment outline.
Questions
Frequently asked questions
What are Sec 1 Science density notes in one line?
Density = mass ÷ volume. Use g/cm³ or kg/m³. An object sinks in a liquid when its density is greater than the density of that liquid, and floats when its density is lower.
How do I find the volume of an irregular solid?
Use displacement. Record the volume of water in a measuring cylinder, lower the solid until it is fully under the water, and subtract the first reading from the second. The difference is the volume of the solid.
What is the difference between a physical property and a chemical change?
A physical property, such as density or melting point, can be measured without turning the material into a new substance. Burning, rusting and reacting with acid make new substances, so they are chemical changes.
Is this chapter in the Sec 1 Science WA1 or the EOY?
Schools often test Exploring Diversity of Matter by Physical Properties in WA1 together with Chapter 1, and again in the end-of-year exam. Check your school’s assessment outline for the exact scope.
Which physical properties should I be able to use?
Electrical conductivity, thermal conductivity, melting and boiling points, strength, hardness, flexibility and density. You should also be able to measure length, mass and volume and use the data to choose a material.
Up next
Chapter 3: Exploring Diversity of Matter by Chemical Composition