Objects, substances and particles
A steel spoon, a steel plate and a steel bucket look different, yet all three are made of steel. The spoon, plate and bucket are objects, and steel is the substance they are made of. If you could look closer and closer, you would find that every substance is made of tiny particles.
Things named by their shape and use are objects (वस्तू). The material an object is made of is the substance (पदार्थ). All substances are made of extremely minute particles (कण).
Rule 1: Object and substance — The same substance can make many objects, and one object can use many substances.
- Easy : Chair – object; wood – substance.
- Medium : A bucket can be of plastic or steel: same object, different substances.
- Exam-type : A pencil has wood, graphite and rubber; many substances in one object.
Rule 2: Particles — Everything – milk, oil, air – is made of particles too small to see.
- Easy : Sparks from a sharpened knife are tiny red-hot iron particles.
- Medium : The smell of incense spreads in the room because its particles scatter.
- Exam-type : Ancient Indian texts mention five elements (Panchtatve): Earth, Water, Fire, Air and Space.
Object = shape and use. Substance = what it is made of.
Using "object" and "substance" as the same word. A scissors is an object; iron is the substance.
Memory clue: Object = Outer form; Substance = Stuff inside.
Spot the difference
| Word | Meaning | Example |
|---|---|---|
| Object | Named by shape and use | Chair, scissors |
| Substance | Material it is made of | Wood, iron |
| Particle | Tiny part of a substance | Iron spark |
Practice questions
- 1What is an object?
- 2What is a substance?
- 3Name the substance of a steel spoon.
- 4What are all substances made of?
- 5Name the five elements (Panchtatve).
- 6Is a pencil an object or a substance? How many substances does it have?
- 7Why does the smell of incense reach the whole room?
- 8Sita says a bucket is a substance. Correct her.
Show answers (try them yourself first)
- 1A thing named by its shape and use.
- 2The material an object is made of.
- 3Steel
- 4Extremely small particles.
- 5Earth, water, fire, air, space.
- 6An object; wood, graphite and rubber (more than one).
- 7Its tiny particles scatter in all directions.
- 8A bucket is an object. Plastic or steel is the substance.
States of matter
Ice from the freezer is hard. Left in a glass, it melts to water. Heat the water and it turns to steam and spreads in the kitchen. It is the same water, in three different forms.
Solid (घन): particles very close and tightly held. Liquid (द्रव): particles loosely bound, so it flows and takes the shape of the container. Gas (वायू): particles independent, scatter in all the space.
In the figure : In a solid (A) the particles are very close and tightly held; in a liquid (B) they are loosely bound; in a gas (C) they are independent and scatter in all the space.
Rule 1: Three states — Solid has a fixed shape. Liquid takes the shape of the container. Gas fills all the space.
- Easy : A pencil (solid) keeps its shape.
- Medium : Milk (liquid) takes the shape of the glass.
- Exam-type : The smell of food (gas) spreads in the whole room.
In the figure : On heating, a solid (1) becomes a liquid (2) and then a gas (3). Only the state changes; the substance is the same.
Rule 2: Change of state — Heating changes a solid to a liquid and a liquid to a gas. Only the state changes.
- Easy : Ice → water → steam.
- Medium : Ghee is solid in cold weather and melts in summer; coconut oil solidifies in winter.
- Exam-type : Lava is molten rock. Liquid nitrogen is used for cooling, liquid oxygen in rockets, and solid carbon dioxide is dry ice.
The state depends on how tightly the particles hold each other and on temperature.
Thinking that steam is a different substance from water. It is water in gas form.
Memory clue: Solid – Close; Liquid – Loose; Gas – Gone everywhere.
Spot the difference
| State | Particles | Shape |
|---|---|---|
| Solid | Very close, tight | Fixed |
| Liquid | Loosely bound | Takes container's shape |
| Gas | Independent | Fills all space |
Practice questions
- 1Name the three states of matter.
- 2Which state has particles very close and tightly held?
- 3Which state takes the shape of its container?
- 4Which state fills all the available space?
- 5What happens when a solid is heated?
- 6What is dry ice?
- 7Why does coconut oil become solid in winter?
- 8Raju says steam is a different substance from water. Correct him.
Show answers (try them yourself first)
- 1Solid, liquid and gas.
- 2Solid
- 3Liquid
- 4Gas
- 5It becomes a liquid.
- 6Solid carbon dioxide
- 7At low temperature the particles hold each other more tightly.
- 8Steam is water in the gas state; only the state changes.
Matter and the plasma state
When you step into a full bathtub, the water level rises and some spills out. The water pushed out by your body shows how much space you take up. Anything that takes up space and has mass is matter.
Matter (द्रव्य) is anything that occupies space and has mass. Everything in the universe – the Sun, stars, comets – is matter. In the Sun and in lightning matter exists as plasma (प्लाझ्मा).
In the figure : A is a solid, B a liquid and C a gas. In lightning (D), where immense energy is created, matter is in the plasma state.
Rule 1: Matter occupies space — Even air is matter – it fills a balloon.
- Easy : A balloon filled with air takes up space.
- Medium : Light and heat are not matter because they have no mass.
- Exam-type : Plasma is the fourth state, found in the Sun and in lightning.
In the figure : The stone pushes the water aside. The rise of the water level, 58 ml − 40 ml = 18 ml, is the volume of the stone.
Rule 2: Volume by displacement — Volume of an object = final water level − starting water level.
- Easy : Water rises from 30 ml to 45 ml: volume = 15 ml = 15 cm³.
- Medium : 100 ml → 120 ml gives 20 ml = 20 cm³.
- Exam-type : A potato dropped in a full container makes water spill equal to its volume.
Matter = space + mass. Solid, liquid, gas and plasma are four states of matter.
Thinking air is not matter because we cannot see it. Air has mass and occupies space.
Memory clue: Matter = Mass + Space.
Spot the difference
| Item | Matter? |
|---|---|
| Air | Yes |
| Sunlight | No |
| Lightning | Yes, as plasma |
Practice questions
- 1What is matter?
- 2Name the state of matter in the Sun.
- 3Name one place on Earth where plasma is found.
- 4Is air matter? Why?
- 5Water rises from 30 ml to 45 ml when a stone is dropped in. Find the volume of the stone.
- 6What does the water level rise show?
- 7Is a shadow matter? Give a reason.
- 8A student says "the stone with the larger mass always raises the water more". Correct him.
Show answers (try them yourself first)
- 1Anything that occupies space and has mass.
- 2Plasma
- 3Lightning
- 4Yes. It has mass and occupies space.
- 515 ml = 15 cm³
- 6The volume of the object.
- 7No. It has no mass and occupies no space.
- 8The rise depends on the volume, not on the mass.
Density
A small stone and a big sponge: which is heavier? The stone feels heavier even though the sponge is bigger. A packed small thing can be heavier than a large light one. Density measures how tightly the matter is packed.
Density (घनता) = mass ÷ volume. Units: g/cm³ or kg/m³. Mass is measured in g or kg; volume of solids in cm³ or m³ and of liquids in ml or L (1 cm³ = 1 ml).
In the figure : A pan balance measures mass. When the beam is level, the mass of the object is equal to the total of the weights: 50 g + 20 g + 10 g = 80 g.
Density
In the app you can move this figure with your finger.
Open in the appRule 1: Finding density — Density = mass ÷ volume.
- Easy : Mass 120 g, volume 40 cm³: density = 120 ÷ 40 = 3 g/cm³.
- Medium : A block 5 × 4 × 2 cm has volume 40 cm³ and mass 312 g: density = 312 ÷ 40 = 7.8 g/cm³.
- Exam-type : Mass from density: density 2.7 g/cm³ and volume 8 cm³ give mass = 2.7 × 8 = 21.6 g.
In the figure : The volume of a block is length × breadth × height = 4 × 3 × 2 = 24 cm³. If its mass is 60 g, its density is 60 ÷ 24 = 2.5 g/cm³.
In the figure : A substance with a density less than that of water (1 g/cm³) floats (P and Q); a denser substance sinks (R and S).
Rule 2: Float or sink — Density less than water (1 g/cm³): floats. More than water: sinks.
- Easy : Wood of density 0.6 g/cm³ floats on water.
- Medium : Oil of density 0.9 g/cm³ floats on water (45 g in 50 ml gives 0.9).
- Exam-type : Gold has density 19.3 g/cm³ and sinks; 10 cm³ of gold has mass 193 g.
Every pure substance has a fixed density. It helps check purity (pure water 1 g/cm³). Tools: measuring cylinder (volume), pan balance (mass).
Thinking the heavier object always sinks. It depends on density, not only on mass.
Memory clue: D = M ÷ V – mass on top, volume at the bottom.
Spot the difference
| Quantity | Unit | Tool |
|---|---|---|
| Mass | g, kg | Pan balance |
| Volume | cm³, ml | Measuring cylinder |
| Density | g/cm³, kg/m³ | Calculated |
Practice questions
- 1Write the formula for density.
- 2Name two units of density.
- 3Find the density: mass 120 g, volume 40 cm³.
- 4Find the volume of a block 5 cm × 4 cm × 2 cm.
- 5Find the density of a block of volume 40 cm³ and mass 312 g.
- 6Does a substance of density 0.6 g/cm³ float or sink in water?
- 7Density of a metal is 2.7 g/cm³. Find the mass of 8 cm³ of it.
- 8Ravi says a heavy iron nail sinks because it is heavy, but a big wooden log floats though it is heavier. What decides it?
Show answers (try them yourself first)
- 1Density = mass ÷ volume.
- 2g/cm³ and kg/m³.
- 33 g/cm³
- 440 cm³
- 57.8 g/cm³
- 6It floats, because 0.6 is less than 1.
- 72.7 × 8 = 21.6 g
- 8Density, not mass alone. Iron is denser than water; wood is less dense.
Optical and magnetic properties
You can see the street clearly through a window glass, but only a blurry shape through a bathroom's frosted glass, and nothing at all through a wall. Substances behave differently with light.
Transparent (पारदर्शक) substances let light pass fully. Translucent (अर्धपारदर्शक) let a little pass. Opaque (अपारदर्शक) let none pass. Magnetic substances are attracted by a magnet.
In the figure : The star is seen clearly through the transparent panel (A), faintly through the translucent panel (B) and not at all through the opaque panel (C).
Rule 1: Light and substances — Transparent – clear. Translucent – blurry. Opaque – nothing.
- Easy : Clear glass and clean water are transparent.
- Medium : Butter paper, oily paper and frosted glass are translucent.
- Exam-type : Wood, cardboard, metal sheet and soil are opaque.
Rule 2: Magnetic substances — Iron, nickel and cobalt are attracted by a magnet.
- Easy : An iron nail sticks to a magnet.
- Medium : Aluminium foil, copper wire and wood do not stick.
- Exam-type : A magnet can sort iron from other metals in scrap.
Magnetic materials: iron, nickel, cobalt. Light: Transparent > Translucent > Opaque.
Calling butter paper transparent. It is translucent because you see only a blur.
Memory clue: Transparent = clear; Translucent = a little; Opaque = none.
Spot the difference
| Type | Light passes | Example |
|---|---|---|
| Transparent | Fully | Clear glass |
| Translucent | A little | Butter paper |
| Opaque | None | Wood |
Practice questions
- 1Define transparent.
- 2Give two translucent materials.
- 3Give two opaque materials.
- 4Name three magnetic substances.
- 5Is clean water transparent, translucent or opaque?
- 6Is a copper wire attracted by a magnet?
- 7Why is frosted glass used in bathroom windows?
- 8A student says butter paper is transparent as we can see light through it. Correct him.
Show answers (try them yourself first)
- 1A substance that lets light pass through completely.
- 2Butter paper and frosted glass.
- 3Wood and metal sheet.
- 4Iron, nickel and cobalt.
- 5Transparent
- 6No
- 7It lets light in but gives privacy because we cannot see clearly through it.
- 8Only a little light passes and objects look blurry, so it is translucent.
Quick revision
- Solid, liquid, gas (and plasma) are states of matter.
- Density = mass / volume.
- Transparent, translucent, opaque.
- Magnetic: iron, nickel, cobalt.