Grade 5 Chapter 24: Substances, Objects and Energy

Topics covered: Substances and objects, States of substances (solid, liquid, gas), Changes in state, Energy, Forms of energy, Uses of energy.

Can you tell?

1. What is a substance?
2. What is an object?
3. What is the difference between a substance and an object?

Substances and Objects

We see many things around us. They are all made of certain substances. For example, a chair is an object made of wood. Wood is the substance. A glass is an object made of glass. Glass is the substance. A shirt is an object made of cotton. Cotton is the substance.

An object is something that has a definite shape and can be seen or touched. A substance is the material of which an object is made. One substance can be used to make many objects. For example, wood can be used to make a chair, a table, a door, a window, etc. Also, one object can be made of different substances. For example, a chair can be made of wood, plastic, or metal.

[Note: Students should refer to the image showing various objects made from different substances on page 127 of their textbook.]

Think about it.

What are the objects in your classroom made of?

States of Substances

Substances exist in three main states: solid, liquid, and gas.

Solid State

A solid has a definite shape and a definite volume. It does not change its shape easily. Examples: a stone, a piece of wood, ice, a book.

[Note: Students should refer to the image showing solids on page 128 of their textbook.]

Liquid State

A liquid does not have a definite shape, but it has a definite volume. It takes the shape of the container it is poured into. Examples: water, milk, oil, juice.

[Note: Students should refer to the image showing liquids on page 128 of their textbook.]

Gaseous State

A gas does not have a definite shape or a definite volume. It spreads out to fill the entire container it is in. Examples: air, water vapour, cooking gas (LPG).

[Note: Students should refer to the image showing gases on page 128 of their textbook.]

Try this.

Materials: A glass of water, a few ice cubes, a pan with a lid.

Procedure:

1. Put some ice cubes in a glass. Observe what happens as the ice melts.
2. Heat some water in a pan with a lid. Observe the steam coming out and the droplets forming on the lid.

What do you see?

Ice (solid) melts into water (liquid). When water (liquid) is heated, it turns into steam (gas). When steam (gas) touches a cold surface, it turns back into water (liquid).

Changes in State

When a substance changes from one state to another, it is called a change of state. Heat plays an important role in these changes.

• Melting: Solid to liquid (e.g., ice to water). This happens when a solid gains heat.
• Evaporation: Liquid to gas (e.g., water to water vapour). This happens when a liquid gains heat.
• Condensation: Gas to liquid (e.g., water vapour to water droplets). This happens when a gas loses heat.
• Freezing: Liquid to solid (e.g., water to ice). This happens when a liquid loses heat.

[Note: Students should refer to the diagram showing changes of state on page 129 of their textbook.]

Do you know?

Water exists in all three states: as ice (solid), water (liquid), and water vapour (gas).

Use your brain power!

What happens to a candle when it burns? Does it change its state?

Energy

Can you tell?

• What do you need to run, play, or study?
• What makes a fan rotate or a car move?

We need energy to do any work. Energy is the ability to do work. Without energy, nothing can move or change. We get energy from the food we eat. Machines get energy from fuel or electricity.

[Note: Students should refer to the image showing various activities requiring energy on page 130 of their textbook.]

Forms of Energy

Energy exists in different forms:

• Heat Energy: We get heat from the sun, burning fuel, or electricity. Heat helps us cook food, keep warm, and dry clothes.
• Light Energy: We get light from the sun, electric bulbs, and fire. Light helps us to see things.
• Sound Energy: We hear sounds from various sources like musical instruments, speakers, or vehicles. Sound is a form of energy.
• Mechanical Energy: This is the energy of movement. A moving car, a rotating fan, or a person running all have mechanical energy.
• Electrical Energy: This is the energy we get from electricity. It powers our lights, fans, televisions, and many other appliances.
• Chemical Energy: This energy is stored in substances like food, fuels (petrol, diesel), and batteries. It is released when these substances undergo chemical changes.

[Note: Students should refer to the images showing different forms of energy on page 131 of their textbook.]

Think about it.

How does the sun provide us with different forms of energy?

Uses of Energy

Energy is used for countless purposes in our daily lives:

• Cooking: Heat energy from gas or electricity.
• Lighting: Electrical energy for bulbs.
• Transport: Chemical energy from fuel in vehicles.
• Running Machines: Electrical or mechanical energy.
• Growth and Movement: Chemical energy from food in our bodies.

We use energy all the time, directly or indirectly. It is important to use energy wisely and conserve it.

What's the solution?

Your friend leaves the lights and fan on in an empty room. What would you tell your friend?

Always remember -

Energy cannot be created or destroyed, but it can be changed from one form to another. We must use energy carefully and avoid wasting it.

What we have learnt -

• An object is made of one or more substances.
• Substances exist in three states: solid, liquid, and gas.
• Substances can change from one state to another (melting, evaporation, condensation, freezing) due to gain or loss of heat.
• Energy is the ability to do work.
• Energy exists in various forms: heat, light, sound, mechanical, electrical, and chemical energy.
• Energy is essential for all activities, and we must use it wisely.

Exercises

1. Fill in the blanks.
   1. A chair is an __________ made of wood.
   2. Water is a __________ that exists in three states.
   3. When a liquid gains heat, it turns into a gas, a process called __________.
   4. The ability to do work is called __________.
   5. Light and sound are forms of __________.
2. Answer the following questions.
   1. What is the difference between a substance and an object?
   2. Name the three states of substances with one example each.
   3. What is a change of state? Give an example.
   4. List any three forms of energy.
   5. Why is it important to conserve energy?
3. Classify the following into solids, liquids, and gases:

   Stone, milk, air, ice, juice, oxygen, book, water vapour.

   • Solids: Stone, Ice, Book
   • Liquids: Milk, Juice
   • Gases: Air, Oxygen, Water vapour
4. Match the following:

   Column A	Column B
   1. Melting	a. Liquid to solid
   2. Evaporation	b. Solid to liquid
   3. Freezing	c. Liquid to gas

Activities

1. Observe different objects at home and identify the substances they are made of.
2. Conduct a small experiment to show evaporation (e.g., leaving a wet cloth in the sun).
3. Make a list of all the electrical appliances in your home and discuss how they use energy.