Answer: A force is a push or a pull.

Answer: It is a pull. You pull the rope towards you.

Answer: Muscular force, gravity, friction and magnetic force.

Answer: True. Pressing dough with your hands changes its shape.

Answer: Friction between the tyres and the road slows it down until it stops.

Answer: Gravity is the pull of the Earth on everything. Example: a mango falls from the tree.

Answer: A force can make a thing move, stop it, change its speed, change its direction, or change its shape.

Answer: Work is done when a force makes a thing move in the direction of the force.

Answer: Work = Force × Distance. The unit is the joule (J).

Answer: Work = 10 × 3 = 30 joules.

Answer: False. The bag does not move, so no work is done.

Answer: The distance moved is 0. Work = Force × 0 = 0 joules.

Answer: Energy is the ability to do work. It is measured in joules.

Answer: Kinetic energy is the energy of a moving thing, like a rolling ball. Potential energy is stored energy, like a ball held high.

Answer: Chemical energy in the battery changes to electrical energy, and then to light energy (and a little heat).

Answer: From the food we eat. Food gets its energy from the Sun through plants.

Answer: Energy cannot be made or destroyed. It only changes from one form to another.

Answer: Renewable: sunlight and wind. Non-renewable: coal and petrol.

Answer: False. Coal takes millions of years to form, so it cannot be replaced easily. It is non-renewable.

Answer: The Sun gives light and heat. Plants use sunlight to grow, we eat plants for food energy, and solar panels turn sunlight into electricity.

A force is a push or a pull. Force can make things move. Kicking a football is a push, and drawing water from a well is a pull.

Muscular force, such as a bullock pulling a cart. Gravity, such as a mango falling from a tree. Friction, such as a rolling cycle stopping. Magnetic force, such as a magnet picking up pins.

Gravity is the pull of the Earth. It pulls everything towards the Earth. That is why a mango falls down from the tree, and why we stay on the ground and do not float away.

Friction is the force that slows things down when two surfaces rub against each other. When we stop pedalling, friction between the wheels and the road slows the cycle until it stops.

A force can make a thing move, stop a moving thing, change its speed, change its direction and change its shape. For example, pressing dough into a roti changes its shape.

Work is done only when a force is applied and the thing moves in the direction of the force. If a thing does not move, no work is done, even if we push a wall with a big force.

Work = Force × Distance. Force is measured in newton (N), distance in metre (m) and work in joule (J). One joule is equal to one newton multiplied by one metre.

Work = Force × Distance = 10 N × 3 m = 30 J. So the boy does 30 joules of work. We must always write the unit joule after the answer.

Energy is the ability to do work. We need it to run, jump, play and think. Like work, energy is measured in joules. A car needs petrol and our body needs food to get energy.

Energy cannot be made and it cannot be destroyed. It only changes from one form to another, and the total energy always stays the same. For example, in a doorbell, electrical energy changes to sound energy.

Introduction: A force is a push or a pull. A push moves a thing away from us, and a pull brings it closer.

Main points: Muscular force is the force from our muscles, as when a bullock pulls a cart or we lift a school bag. Gravity is the pull of the Earth, which pulls everything down. Friction is the force that slows things down when two surfaces rub, and it also helps us to walk and grip things. Magnetic force is the pull or push of a magnet. Kicking a football and pressing a bell are pushes, while pulling a door and drawing water from a well are pulls.

Example: A mango falls from the tree because of gravity, and a magnet picks up pins because of magnetic force.

Conclusion: Force is a push or a pull, and it acts on every thing around us.

Introduction: A force cannot be seen, but we can see what it does. Force has five effects.

Main points: A force can make a thing move, such as when we kick a ball at rest. It can stop a moving thing, such as when a wicketkeeper catches the ball. It can change the speed of a thing, such as when we pedal harder or press the brake. It can change the direction of a thing, such as when a batsman hits the ball back. It can also change the shape of a thing, such as when we press dough into a roti.

Example: In a game of cricket, we can see all five effects of force.

Conclusion: Whenever a thing starts moving, stops, speeds up, turns or changes its shape, a force is acting on it.

Introduction: Friction is the force that opposes motion between two touching surfaces. It acts when two surfaces rub against each other.

Main points: Friction slows things down and can stop them. A rolling cycle stops after we stop pedalling because of friction. People often think friction only stops things, but it also helps us. It lets us walk without slipping and lets us grip things like a pencil or a glass. Without friction, we could not walk or hold anything. Friction also makes surfaces rub away and become warm.

Example: Brakes use friction to stop a cycle, and a rough sole helps a shoe to grip the floor.

Conclusion: Friction is a force that is both a helper and an obstacle in our daily life.

Introduction: In daily life we say work for homework or an office job, but in science work means something special.

Main points: Work is done only when a force is applied and the thing moves in the direction of the force. Work = Force × Distance. Force is measured in newton, distance in metre and work in joule. Work is done when we push a box, pull a cart or lift a bucket. Work is not done when we push a wall that does not move, because the distance is 0 m, so the work is 100 × 0 = 0 J.

Example: Pulling a cart with 20 N over 5 m is 20 × 5 = 100 J of work. Holding a bag for an hour is not work in science, because there is no movement.

Conclusion: In science, no movement means no work, and tiredness alone does not prove that work was done.

Introduction: Work is found by multiplying the force by the distance moved in the direction of the force. Work = Force × Distance.

Main points: In (a), the force is 50 N and the distance is 2 m, so the work done is 50 × 2 = 100 J. In (b), the force is 100 N but the wall does not move, so the distance is 0 m. The work done is 100 × 0 = 0 J. In the formula we must multiply force and distance, not add them. We must also write the units N, m and J.

Example: One joule is about the work done in lifting a small apple up by about 1 metre.

Conclusion: Work is done in case (a) but not in case (b), even though a bigger force was used in (b).

Introduction: Energy is the ability to do work. It is measured in joules, like work.

Main points: Kinetic energy is the energy of a moving thing, like a running boy. Potential energy is stored energy, like a stretched rubber band. Heat energy makes things warm and is used for cooking. Light energy helps us see and comes from the Sun and a torch. Sound energy is made by vibrating things like a bell. Electrical energy runs fans, lights and the TV. Chemical energy is stored in food, fuel and batteries, and our body uses it to give muscular energy.

Example: A fast cricket ball has kinetic energy, and a ball held high has potential energy.

Conclusion: Energy comes in many forms, and every action around us uses some form of energy.

Introduction: Energy does not stay in one form. It keeps changing into other forms.

Main points: In a torch, chemical energy of the battery changes to electrical energy and then to light with a little heat. In a ceiling fan, electrical energy changes to kinetic energy and a little sound. In a solar panel, light energy of the Sun changes to electrical energy. In our body, the chemical energy of food changes to muscular energy and heat. The Law of Conservation of Energy says that energy cannot be made or destroyed. It only changes form, and the total energy always stays the same.

Example: In a doorbell, electrical energy changes to sound energy.

Conclusion: Energy is never lost. It only changes its form, and some of it becomes heat that we cannot use.

Introduction: We get energy from different sources. They are of two kinds, renewable and non-renewable.

Main points: Renewable sources never run out, and nature gives them back. Sunlight, wind and flowing water are renewable. Non-renewable sources are limited and take millions of years to form. Coal, petrol, diesel and natural gas are non-renewable. They are called fossil fuels because they are made from very old plants and animals. Once we use them up, they will not come back in our lifetime. So we should save them and use more sunlight and wind.

Example: A solar panel uses sunlight, and a windmill uses wind, and both are renewable sources.

Conclusion: We should use energy carefully, switch off lights and fans when not in use, and prefer renewable sources.

Introduction: Force, work and energy are different things, but they are connected like links in a chain.

Main points: Rohan had paratha and milk for breakfast, which had chemical energy. His muscles used this energy to give a force on the ball when he threw it. The ball moved 20 metres in the direction of the force, so work was done. The moving ball had kinetic energy, and at the top of its path it had potential energy. When his friend caught the ball, the energy changed to a little heat and sound. Energy was not lost. It only changed form.

Example: When we do 100 joules of work, we spend about 100 joules of energy. That is why we feel hungry after playing.

Conclusion: Energy gives force, force does work, and work changes energy into a new form.

Introduction: Force, work and energy are related, but they do not mean the same thing.

Main points: Force is a push or a pull, and it is measured in newton. Work is a force moving a thing in the direction of the force, and it is measured in joule. Energy is the ability to do work, and it is also measured in joule. Students often think that force is only a push, but a pull is also a force. They think that energy is used up, but it only changes form. They also think that a tired person has done work, but in science, work needs movement.

Example: Pulling a door is a force. Pulling the door open through 1 m is work. The food we ate gave the energy to do it.

Conclusion: We should learn the three words with their meanings and units, and not mix them up.