Matter | ICSE Class 6 Physics Notes

This note covers matter, mass and volume, atoms and molecules, the properties of solids, liquids and gases, shape and texture, comparisons between states, and classification through observations of familiar materials.

What is matter, and how do mass and volume describe it?

Definition: Matter is anything that occupies space and has mass. Mass is the quantity of matter in an object. Volume is the space occupied by matter.

A block of wood, milk and air are examples of matter. They look and behave differently, but each has mass and occupies space. Matter includes materials that keep their own shape and materials that take the shape of their surroundings.

What does mass tell us?

Mass describes how much matter an object contains. When comparing objects by weighing them, the heavier object has more mass and the lighter object has less mass. A balance is an instrument used to measure mass.

An object's mass and its shape answer different questions. Mass concerns the quantity of matter, while shape concerns its form. A description of matter therefore needs more than a statement about what an object looks like.

What does volume tell us?

Volume tells us how much space matter occupies. Water takes up space inside a tumbler. In identical tumblers, the water in a half-filled tumbler occupies less space than the water in an almost completely filled tumbler.

The tumblers can hold the same maximum amount, yet contain different volumes of water. Their capacity, meaning the amount each container can hold, must be distinguished from the volume of water actually present.

Photograph: “Glass tumblers with varying levels of water”. The image shows two glass tumblers with different water levels. The left image is labelled “(a) Half-filled”; the right is labelled “(b) Fully-filled”. Compare the space occupied by water in each tumbler.

See Fig. 6.8 in your NCERT textbook

Air also belongs to matter, even though we do not see it as we see a block of wood. Visibility is not part of the definition of matter. The important properties are having mass and occupying space.

What is matter made of?

Matter is made of tiny particles, meaning very small constituents of matter. These include atoms and molecules. An atom is a tiny building block of matter. A molecule is a group of atoms joined together that can exist independently and retain the properties of the substance.

Atoms and molecules are so small that they cannot be seen with the naked eye, meaning the eye without an instrument to help it see. Seeing an object does not mean that we can see the individual particles of which it is made.

How are particles different from the objects we handle?

A block of wood is an object that can be observed directly. The tiny particles making up matter are at a very different scale. Do not confuse a whole visible object with a single atom or molecule.

The word composition means what something is made of. When describing the composition of matter here, the central idea is that matter has tiny constituents. When describing its state, the question is instead whether it is solid, liquid or gas.

A state of matter is a physical form in which matter exists. Solid, liquid and gas are the three states considered here. These names describe differences in properties such as shape and volume; they do not mean that only solids contain particles.

What can direct observation establish?

We can observe a block of wood keeping its shape or water changing shape when poured. These observations describe the behaviour of visible samples. They do not amount to seeing the atoms or molecules inside those samples.

Note: “Too small to see” does not mean “absent”. Matter contains tiny particles even when its individual atoms and molecules cannot be seen with the naked eye.

Keep the two levels of description clear: an object or sample is what we examine, while particles are its tiny constituents. Matter's composition and its observable properties are connected ideas, but they answer different questions.

Which properties help us describe and classify matter?

A property is a characteristic used to describe a material or object. Shape, texture and volume are useful properties of matter. Classification means arranging objects or materials into groups on the basis of properties they share.

How do shape, texture and volume differ?

Shape is the form or outline of an object or sample. Texture describes its surface, for example whether it is rough or smooth. Volume describes the space it occupies. These terms should not be used as though they mean the same thing.

Hardness concerns how difficult it is to compress or scratch a material. To compress means to squeeze into a smaller space. Materials that can be compressed or scratched easily are described as soft; those difficult to compress or scratch are described as hard.

Hardness and softness are relative properties: their description depends on comparison. Rubber is harder than sponge but softer than iron. Keep both parts of this comparison, because calling rubber simply “hard” loses the comparison that gives the description its meaning.

How should observations be recorded?

A qualitative observation describes a quality without giving a numerical measurement. “The water takes the shape of the container” is qualitative. It reports behaviour that can help us distinguish a liquid from a solid.

Choose the property before making the groups. Grouping by surface texture answers a different question from grouping by state. Record what is observed under the correct heading, then compare the samples using the same property.

A change in one property does not by itself establish a change in every other property. Water, for example, can change shape when transferred while its volume remains constant. The observation should state both features accurately.

What are the distinguishing properties of solids?

A solid has a definite shape and a definite volume. “Definite” means fixed for the sample being considered. A block of wood is an example: its shape is its own, rather than the shape of the container in which it is placed.

What happens when a solid is moved between containers?

Consider an ice cube. Ice is water in the solid state. If an ice cube is transferred from one container to another of a different shape, it retains its shape while it remains solid. Merely changing the container does not make it take the container's shape.

Ice does not flow or spread as liquid water does. Here, flow means movement of the material from place to place as when water is poured. Spreading means extending into the surrounding available space.

1. Place an ice cube in a container and observe its outline.
2. Transfer it to a container with a different shape.
3. Compare the cube's outline before and after the transfer while it remains ice.
4. Record that the solid retains its shape instead of adopting the shape of the new container.

Draw an ice cube in one container and the same cube in a differently shaped container. Keep the cube's outline unchanged. Label the cube “ice: solid” and show that the container's outline differs from the cube's.

Which examples belong to the solid state?

Stones, wood and glass are further examples of solids. Their appearance need not be identical for them to belong to the same state. Classification depends on their distinguishing properties, rather than on all examples looking alike.

Keep a description of shape separate from a description of surface texture. Saying that a solid has a definite shape does not describe whether its surface is rough or smooth. Those are different observations about the material.

The ice-cube comparison is useful because the container changes while the solid's outline remains the same. Record this limited conclusion accurately: the observation concerns an ice cube while it remains in its solid state.

What are the distinguishing properties of liquids?

A liquid has a definite volume but does not have a definite shape. It takes the shape of the container in which it is kept. Water, milk and oil are examples of liquids.

What changes when water is poured?

When water is poured from one container into another of a different shape, the water flows and changes shape. For the same water transferred without loss, its volume remains constant. “Constant” means unchanged during the comparison.

Do not confuse a differently shaped sample with a larger or smaller amount of water. Shape describes its form; volume describes the space it occupies. The same water can have a different form after transfer without having a different volume.

1. Observe water in a container and note the shape it takes.
2. Pour the water into a differently shaped container without spilling any.
3. Observe that the water flows during the transfer and takes the new container's shape.
4. Record the change in shape separately from the unchanged volume of the transferred water.

Draw water in a container and then the same water in a differently shaped container. Label each sample “liquid water”. Add the statements “shape changes” and “volume remains constant”.

Can a liquid spread?

Water poured on a clean surface spreads. This is another observable property of liquid water. It can spread while keeping its volume constant, so spreading is not itself evidence that the amount of water has increased.

Compare this behaviour with ice: ice retains its shape and does not flow or spread. Water flows, changes shape and can spread. These observations distinguish the liquid sample from the solid sample without requiring a numerical calculation.

Note: A liquid having “no definite shape” still has a shape in its container. The phrase means that the liquid does not retain a shape of its own when placed in a differently shaped container.

What are the distinguishing properties of gases?

A gas has neither a definite shape nor a definite volume. It spreads into the available space. Air is an example of matter in the gaseous state. Its lack of a fixed shape does not mean that it lacks matter's basic properties.

How does water vapour behave?

Water vapour is water in the gaseous state. It spreads throughout the entire available space. It has no fixed shape. Water vapour exists even at room temperature, meaning the temperature of the surrounding room, although it is invisible to us.

Water vapour is present in the air around us. Its invisibility provides an important reminder: observing matter does not always mean seeing the matter directly. We should not use visibility as the test of whether something is matter.

Oxygen and carbon dioxide are other examples of gases. These are names of substances, while “gas” names their state. No chemical symbols are needed to compare their state with that of liquid water or solid wood.

How is a gas different from a liquid?

A liquid and a gas both lack a definite shape, so this property alone does not distinguish them. The important additional comparison is volume: a liquid has a definite volume, whereas a gas spreads into the whole available space.

The phrase no definite volume does not mean “no volume”. A gas occupies space, but does not retain a fixed volume of its own. This distinction is essential when explaining why air is matter.

For a complete comparison, describe both shape and volume. Saying merely that a sample takes the shape of its container leaves open whether it behaves as a liquid or as a gas.

How do the three states compare through the example of water?

Water can be observed in three states: ice, liquid water and water vapour. The state names describe different physical forms of water. Comparing these forms helps separate the identity of the substance from its observable behaviour.

What stays clear when the states are compared?

Ice is the solid form, water is the liquid form, and water vapour is the gaseous form. These examples should be compared using the same properties. A statement about ice's shape should be matched with statements about the shape of water and water vapour.

This comparison shows why shape alone is insufficient. Both liquid water and water vapour lack a fixed shape. Volume and the extent of spreading provide the additional features needed to distinguish them.

How should a comparison be expressed?

Start with the property, then describe each state. For shape, say that ice retains its shape, liquid water takes the container's shape, and water vapour has no fixed shape. For volume, distinguish the fixed volumes of solid and liquid samples from the unfixed volume of a gas.

Keep the comparison about the state being observed. Ice is being considered while solid; liquid water is being considered while liquid. A statement about one state should not be applied unchanged to the other states of the same substance.

The contrast between ice and water also shows why touch alone is not the whole explanation. Ice feels hard and can be held in the hand, whereas water cannot be held in the same way. Shape, flow and volume give a fuller description.

How can observations be used to classify familiar materials?

To classify by state, place a material in the solid, liquid or gas group using its distinguishing properties. Begin with what is observed, identify the relevant properties, and then state the classification with a reason.

What is a useful sequence for classification?

1. Identify the sample being considered, such as wood, milk or air.
2. Describe whether it retains its own shape or has no definite shape.
3. Describe whether its volume is definite or whether it spreads into the available space.
4. Use the combined properties to classify it as solid, liquid or gas and explain the choice.

For a block of wood, a definite shape and volume support classification as a solid. For milk, taking the container's shape while having a definite volume supports classification as a liquid. For air, having neither a definite shape nor a definite volume supports classification as a gas.

How can the reason be checked?

Check that the reason actually distinguishes the chosen group. “It is matter” is true of all three groups, so it does not explain why something is a liquid. “It occupies space” is also shared by solids, liquids and gases.

Likewise, “it has no definite shape” needs a volume comparison to distinguish a liquid from a gas. A useful explanation links the observed sample to the combination of properties that identifies its state.

Record texture separately when describing a surface. Roughness or smoothness adds useful information about a sample, but the classification by state still needs the shape and volume comparison. Keeping the observation headings distinct makes the reasoning easier to check.

Glossary

• Matter — Anything that has mass and occupies space, including solids, liquids and gases.
• Mass — The quantity of matter contained in an object or sample.
• Volume — The space occupied by an object or a sample of matter.
• Atom — A tiny building block of matter that cannot be seen with the naked eye.
• Molecule — A group of atoms joined together, capable of independent existence and retaining the substance's properties.
• State of matter — A physical form of matter, such as solid, liquid or gas.
• Solid — A state of matter having a definite shape and a definite volume.
• Liquid — A state of matter with definite volume that takes the shape of its container.
• Gas — A state of matter having neither a definite shape nor a definite volume.
• Texture — The character of a material's surface, described for example as rough or smooth.
• Classification — Arranging objects or materials into groups according to properties they share.
• Qualitative observation — A description of a quality or behaviour without giving a numerical measurement.
• Water vapour — Water in its gaseous state, invisible to us and present in the air.

Common errors and misconceptions

• Misconception: Air is not matter because we cannot see it. Correct: Air has mass and occupies space. Matter need not be visible to us; visibility is not part of its definition.
• Misconception: A gas has no volume. Correct: A gas has no definite volume. It occupies space and spreads into the available space, rather than retaining a fixed volume.
• Misconception: A liquid has no shape at all. Correct: A liquid has no definite shape of its own. It takes the shape of the container in which it is kept.
• Misconception: Water's volume must change when its shape changes. Correct: The same water transferred without loss takes a new container's shape while its volume remains constant.
• Misconception: Atoms and molecules can be seen whenever we look at an object. Correct: The object may be visible, but its atoms and molecules are too small to see with the naked eye.
• Misconception: Roughness and hardness mean the same thing. Correct: Roughness describes surface texture. Hardness concerns difficulty in compressing or scratching a material, and hardness comparisons are relative.
• Misconception: Having no definite shape proves that a sample is liquid. Correct: Gases also lack definite shape. Compare volume as well: liquids have definite volume; gases do not.

Exam-style questions with model answers

Q1. Define matter and volume. [2 marks]

1. Matter is anything that has mass and occupies space.
2. Volume is the space occupied by an object or a sample of matter.

Q2. Name the tiny constituents of matter and explain why they cannot be seen with the naked eye. [2 marks]

1. Matter is made of tiny particles called atoms and molecules.
2. These particles are so small that the naked eye cannot see them, even when the whole object is visible.

Q3. A block of wood retains its shape and volume. Milk takes its container's shape but has a definite volume. Air has neither a definite shape nor a definite volume. Classify each by state and give the reason. [3 marks]

1. The block of wood is a solid because it retains its own shape and has a definite volume.
2. The milk is a liquid because it has a definite volume but takes the shape of the container in which it is kept.
3. The air is a gas because it has neither a definite shape nor a definite volume of its own.

Q4. Water is poured without loss into a differently shaped container. It flows during transfer, adopts the new container's shape and keeps the same volume. State its state of matter, then explain what the observations show about flow, shape and volume. [4 marks]

1. The sample is liquid water. Its combination of a definite volume and a shape determined by its container identifies the liquid state.
2. The water flows during transfer, showing that it can move from one container into another when poured.
3. Its shape changes to match the new container, so it has no definite shape of its own.
4. Its volume remains constant because the same water is transferred without loss; a change of shape does not require a change of volume.

Q5. Ice retains its shape and has a definite volume. Liquid water takes its container's shape but keeps a definite volume when the same water is transferred without loss. Water vapour spreads throughout the available space and has neither a definite shape nor a definite volume. Compare the shape and volume of each state, giving one point for each property of each state. [6 marks]

1. Ice has a definite shape: its own outline is retained instead of changing to match the container in which it is placed.
2. Ice has a definite volume: the solid sample occupies a fixed amount of space while being considered in that state.
3. Liquid water has no definite shape of its own: it takes the shape of the container that holds it.
4. Liquid water has a definite volume: changing its container does not change the volume of the same water transferred without loss.
5. Water vapour has no definite shape: it spreads throughout the available space instead of retaining an outline of its own.
6. Water vapour has no definite volume: as a gas, its occupied space is not restricted to a fixed volume of its own.

Q6. In an observation, an ice cube retains its outline after transfer to a differently shaped container. Water flows, takes a new container's shape and keeps the same volume when transferred without loss. Water vapour spreads throughout the available space. Use these observations to explain the cube's shape, water's flow, water's shape, water's volume and vapour's spreading. [5 marks]

1. The cube's retained outline shows the definite shape of a solid. It does not take the new container's shape while it remains ice.
2. The water's movement during pouring shows that liquid water flows, allowing it to pass from the original container into the other one.
3. The water's new shape shows that a liquid lacks a definite shape of its own and adopts the shape of its container.
4. The unchanged volume shows that changing the shape of the same water without losing any does not change the space it occupies.
5. The vapour's spreading shows gaseous behaviour: it extends throughout the available space rather than retaining a fixed shape and volume of its own.

Q7. A comparison states that rubber is harder than sponge but softer than iron. Explain what hard and soft mean, and explain why both comparisons should be retained. [3 marks]

1. A hard material is difficult to compress or scratch. Compression means squeezing a material into a smaller space.
2. A soft material is one that can be compressed or scratched easily. The description concerns these responses, rather than surface roughness alone.
3. Hardness is relative: rubber is harder when compared with sponge but softer when compared with iron. Both comparisons are needed to preserve the meaning of the statement.

Q8. A liquid and a gas both lack a definite shape. The liquid has a definite volume; the gas does not. Explain why shape alone is insufficient to distinguish them and identify the distinguishing property given. [2 marks]

1. Shape alone is insufficient because the liquid and the gas both lack a definite shape.
2. Volume distinguishes them: the liquid has a definite volume, whereas the gas has no definite volume.

Key takeaways

• Matter has mass and occupies space; a block of wood, milk and air are all examples of matter.
• Mass describes the quantity of matter, while volume describes the space occupied by that matter.
• Matter contains tiny particles called atoms and molecules, which cannot be seen with the naked eye.
• A solid has definite shape and volume; an ice cube retains its outline when moved between containers while remaining solid.
• A liquid takes its container's shape but has a definite volume, as shown by water transferred without loss.
• A gas has neither definite shape nor definite volume and spreads throughout the available space.
• Texture describes a surface as rough or smooth; hardness concerns difficulty in compressing or scratching a material.
• Classify matter using the combination of shape and volume, since liquids and gases both lack a definite shape.

Test yourself

Which two properties define matter?

Matter has mass and occupies space. Both belong in its definition.

What is the difference between mass and volume?

Mass is the quantity of matter in an object; volume is the space it occupies.

Why can we see an object without seeing its atoms?

The whole object can be visible, while its atoms are too small to see with the naked eye.

What does an ice cube retain when moved to another container while remaining solid?

It retains its own shape instead of taking the shape of the new container.

What changes and what remains constant when the same water is transferred without loss to a differently shaped container?

The water's shape changes to match the new container, while its volume remains constant.

What does “a gas has no definite volume” mean?

A gas occupies space but does not retain a fixed volume of its own.

What is water vapour?

Water vapour is water in the gaseous state. It is invisible to us and present in air.

Why must rubber's hardness be described with the comparison?

Hardness is relative: rubber is harder than sponge but softer than iron.