Chapter 11 — Work and Energy

Force is a push or a pull that can make things move, stop or change shape. When you push a cupboard door to open it, pull a drawer, press a sponge, or kick a ball, you are using force. Forces come from our muscles, from gravity that pulls objects toward the Earth, from magnets that pull or push metallic objects, and from machines such as motors or fans. Every force acts in a particular direction and has a certain amount of strength.

We can describe forces by showing arrows in diagrams. The arrow points in the direction the force acts. A longer arrow tells us the force is stronger while a shorter arrow shows a smaller force. When two forces act on the same object in the same direction, they add up. If they act in opposite directions, they can balance each other; equal opposite forces keep the object still. If one is stronger than the other, the object moves in the direction of the stronger force. For example, when you push a heavy box and someone else pushes from the other side with less force, the box moves in your direction.

Some forces change the shape of objects. Squeezing a ball or stretching a rubber band changes their shape. Other forces only change motion without changing form, like a push that starts a swing. Gravity is always present: it gives weight to objects and pulls them downward. Friction is another force that resists motion; it acts opposite to the direction of movement and is why moving things slow down without continuous pushing.

Simple classroom activities help learn forces: press a sponge, pull a toy car with a string, and observe how different forces make different effects. By noticing direction and strength you begin to understand why things move or stay still. This understanding will be used later to study work and energy.

Work in everyday language means doing a task that needs effort, such as cleaning the house, carrying schoolbooks, cooking or gardening. In school science we use a more exact idea. Work is done when a force makes an object move in the direction of the force. This means three things must happen: there must be a force, the object must move, and the movement must be along the direction of that force.

For example, when you lift a box from the floor to a shelf, your hand applies an upward force and the box moves upward, so you do work on the box. If you push a door and it opens, you do work on the door. But if you push a wall and it does not move, even though you feel you used energy and got tired, in scientific terms no work is done on the wall because there was no movement. Similarly, if you carry a bag while walking horizontally, the force from your hand is vertical (upwards) to hold it, while your movement is horizontal; only the part of force along movement would count for scientific work.

Understanding this helps to separate effort we feel from actual 'work' in science. Holding something steady can be tiring but does not count as work in physics unless there is displacement. Work explains why energy is moved or transferred: when work is done on an object, energy is transferred to it and it may move faster, gain height or change shape. The idea links our muscles, machines and tools — when they do work they transfer energy from one body to another.

Classroom demonstrations make the idea clear. Have students push an immovable object and note no displacement; then push a small trolley and measure movement. Show lifting a book (work) and holding it still (no work). Ask students to list tasks they do at home and say whether they are 'work' in the scientific sense. This practice trains them to use correct scientific terms and to observe forces and motion carefully.

In Class 6 we learn a simple rule to compare how much work is done in different tasks: both the force applied and the distance moved matter. If you push with the same force but move the object a longer distance, the task needs more work. If you lift a heavier object the same distance, it needs more work because the required force is greater. Thus work depends on two things together — how strong the force is and how far the object moves along the direction of that force.

To understand this better try small activities. Take two identical toy cars and push each with the same gentle force; let one travel a short distance and the other a longer distance. Students will notice that moving the car farther takes more energy and time. Another activity is to lift the same weight to different heights; lifting it higher requires more effort and therefore more work. These examples show the combined role of force and distance.

The rule also explains everyday choices. When you use a ramp, you trade a smaller force for a longer distance to reach the same height, which can make lifting easier. If you want to move a heavy load, you can either apply a large force over a short distance, or a smaller force over a longer distance. Tools like levers and pulleys help change how force and distance are applied so tasks feel easier, though the total effort relates to both factors.

Even without numbers, this idea prepares students for later formal study where work is calculated by multiplying force and distance. For now, focus on observing and describing situations where changing force or distance changes how hard a task seems. Ask students to compare pairs of activities and explain which involves more work and why, using the two factors: force and distance.

Energy is the ability to do work or to cause change. When something has energy it can move, heat up, give light, or make sound. People need energy to walk, play and think. Machines need energy to run. Energy is not visible itself, but we see its effects: a moving fan, a warm cup, a bright bulb, or a ringing bell are signs that energy is present and being used.

Energy exists in many everyday items. Food contains chemical energy that our bodies use to work and grow. A charged battery stores energy that can light a torch. A stretched rubber band stores energy until released. Because energy causes change, it links directly with the idea of work: when you push an object and it moves, the energy from your muscles is transferred to the object as motion or stored energy. This is why doing work makes us feel tired — our body spent stored chemical energy.

Energy can be stored and later used. For example, water held in a dam has stored energy because it is higher than the river below; when released it will flow and can turn turbines to make electricity. Energy can also be transferred from one object to another: when a moving ball hits a standing ball, some of its motion energy passes to the second ball and makes it move. Observing such transfers helps students see that energy does not vanish suddenly but moves or changes form.

Understanding energy helps explain everyday processes: why engines need fuel, why electricity runs lights, why food gives strength, and why we should use energy carefully so supplies and the environment are protected. Students should practise naming energy types in daily life and recognise situations where energy is stored, used or changed. Teachers can use simple games: give cards with pictures and ask children to say which form of energy is shown and where it comes from.

Energy appears in many forms and each form is useful for different jobs. For Class 6 students the main forms to learn are mechanical, heat, light, sound, chemical and electrical energy. Knowing these helps us identify how things work in our homes, classrooms and nature.

Mechanical energyHeat energy

Light energySound energyChemical energy

Electrical energy

Many processes use more than one form. A burning candle converts chemical energy into light and heat. An electric iron converts electrical energy into heat to press clothes. A windmill converts wind (mechanical) into electrical energy. Students should practise by finding examples at home and noting the forms of energy before and after the change. Such exercises build clear understanding of how energy is used and transformed in daily life.

Potential energy

Potential energy is not only about height. A stretched rubber band contains elastic potential energy. When you stretch it more, it stores more energy and when released it can fling a paper piece. A compressed spring in a toy car stores energy until the latch is released and the car moves. Food also stores chemical potential energy in its molecules; when the body digests food, that chemical energy becomes available for movement and growth. A battery holds chemical potential energy that can be changed into electrical energy when used in a torch.

There are many classroom activities to identify potential energy. Compare two identical balls, one placed on the floor and another on a chair; the higher ball has more potential energy. Stretch two rubber bands differently and note which launches a paper plane farther. Fill two bottles at different heights with water and see which one makes more splash when released. Also ask students to think of objects that store energy because of their condition — for example, a book closed on a shelf stores gravitational potential energy, and a wound-up toy stores elastic potential energy.

Potential energy is important because it can change into other forms of energy. When a stored object is released, potential energy often becomes kinetic energy or heat or sound. Recognising stored energy helps children understand how machines, toys and nature keep energy ready to do work when needed.

Kinetic energy

When an object moves, we can see kinetic energy in action. A rolling ball can knock over pins, a flowing stream can turn a water wheel, and blowing wind can move leaves and turn windmills. Kinetic energy is also felt: a person running into water will make bigger waves than a person walking slowly. Sometimes moving objects make sound or heat when they collide due to part of kinetic energy changing to those forms.

Kinetic energy often comes from potential energy. For example, a stone placed on a high wall has potential energy; when pushed off, that potential energy changes into kinetic energy as it falls and gains speed. A stretched spring releases its stored energy as motion when it returns to shape. A moving car converts chemical energy from fuel into kinetic energy of the car. Observing these changes helps students connect stored energy and motion energy.

Simple classroom activities help measure effects: roll marbles from different places and note which marble reaches farther or hits harder; drop small paper cones from different heights to see how motion changes. These exercises show that moving objects carry energy that can do work on other things. Ask students to describe everyday examples of kinetic energy and to explain how motion was produced and what effects it made.

Energy transformation means energy changing from one form to another. In daily life energy does not disappear; it moves or changes form. Recognising transformations helps students follow how devices and processes work. For example, a torch uses chemical energy from a battery and changes it into light and some heat when the torch is on. A radio changes electrical energy into sound energy. A moving car engine converts chemical energy of petrol into mechanical energy that moves the vehicle, and also into heat and sound as side effects.

Many simple classroom examples show this change clearly. Rubbing hands turns mechanical energy into heat because friction produces warmth. A toy car that is wound up stores energy as a compressed spring (elastic potential energy) and then when released that energy becomes kinetic energy making the car move. Burning wood or gas converts chemical energy into heat and light used for cooking and warmth.

Teachers should encourage students to trace the energy flow in an activity: identify the starting form, the intermediate steps and the final form. For instance, in a coal-powered lamp the sequence is chemical energy in coal -> heat energy from burning -> heat makes steam -> steam moves turbine (mechanical energy) -> generator converts mechanical energy into electrical energy -> electricity lights our bulbs (light energy). Even though we do not study conservation with numbers in Class 6, these examples show that energy is transferred and appears in different forms, which is important to understand how machines and nature provide power.

Practicals like a dynamo on a bicycle (mechanical to electrical to light) or a simple demonstration of a candle (chemical to heat and light) help make the idea clear and memorable.

People obtain energy from different sources and it is useful to group them as renewable and non-renewable. Renewable sourcesNon-renewable sources

Solar energy is available each day and can be used directly for heating water, lighting and by solar panels to make electricity. Wind energy uses the motion of air to turn turbines so electricity can be produced. Hydropower uses the energy of falling or flowing water stored behind dams or in rivers; when water flows down it turns turbines and generates electricity that lights homes and runs machines. Biomass such as wood, animal waste and crop residue can be burned for heat or converted into biogas; such sources are renewable when managed properly.

Fossil fuels — coal, oil and natural gas — have been the main energy sources for many years. They store chemical energy formed from plants and animals over millions of years. When burned they give large amounts of heat for factories, vehicles and power plants, but they produce smoke and harmful gases that pollute the air and cause health issues. Also, because they take a very long time to form, they are called non-renewable and will run out if used too quickly.

In everyday life students see a mix: a village stove may use wood or cow-dung (renewable if collected carefully), a car uses petrol (non-renewable), and many homes now use electricity partly made by coal plants and partly by hydropower or solar panels. Teachers can ask students to list what powers lights, cooking, transport and heating in their homes and to mark each source as renewable or non-renewable. This activity builds awareness about choices and encourages thinking about cleaner options and saving energy for the future.

Simple machines are devices that help us change the size or direction of a force so that tasks become easier to perform. Although they do not reduce the total amount of work needed (ignoring friction), they let us apply smaller force over a longer distance, or change a difficult push into a more comfortable pull. Common simple machines students should know include the lever, pulley, inclined plane (ramp), wheel and axle, screw and wedge.

A lever is a rigid bar that rests on a pivot called a fulcrum. By placing the fulcrum closer to the load you can lift heavy objects with less effort. Examples are seesaws, crowbars and scissors (a pair of levers). A pulleyinclined plane or ramp lets you raise a heavy object to a height by pushing it up along a slope; the force needed at any moment is less though you move the object over a longer distance. Staircases and loading ramps are everyday inclined planes.

Other simple machines include the wheel and axle which reduces friction and makes movement smoother (like carts and bicycles), screws which convert turning force into upward motion (jacks, screws) and wedges which help split or cut objects (axe, knife). Simple experiments help understanding: compare lifting a small box straight up with pushing it up a ramp; students will see the ramp needs less immediate force even though the box travels a longer distance. Using a pulley to lift a bucket shows how direction and number of pulleys change the effort. Learning about simple machines helps children see the clever ways people design tools to reduce effort and make life easier.

In science we say no work is done when a force does not cause movement in the direction of that force. This idea may seem strange because people can feel tired while doing such activities, but the scientific definition requires displacement along the force direction. For example, if you hold a heavy bag in your hand and stand still, your muscles apply an upward force to support the bag and you may feel tired. Nonetheless the bag does not move in the upward direction, so by the scientific rule no work is done on the bag while you hold it stationary.

Other common examples include pushing a closed wall that does not move, or trying to move a stuck object without success. Even when you push hard, if the object does not move in the force direction, no work is counted in physics. Another situation is carrying a bag while walking on a straight path: the supporting force from your hand is upward while your movement is horizontal; since the main force is not along the movement, the scientific work done by your hand in the horizontal direction is zero — only parts of force along motion count.

Friction and other resisting forces can cause a difference between feeling tired and doing scientific work. For instance, if you pedal a bicycle against friction and the bicycle does not move, your muscles consume energy but no mechanical work is transferred to the bicycle because there is no displacement. Teachers can demonstrate this with safe examples: pushing a door that is locked (no movement), holding a book still on the head (no vertical displacement), and then letting the book be lifted and placed on a table (work occurs during lifting). These activities help students understand the precise conditions needed to say that work is done and separate everyday feelings of effort from the physics definition.

Saving energy means using less energy to do the same job so that resources last longer and pollution is reduced. For Class 6 students it is important to learn simple habits that save energy every day. Small actions at home and school, when done by many people, make a big difference. Understanding sources of energy and how they are used helps children choose better options and form good habits early.

At home, simple ways to save energy include switching off lights and fans when not in use, using energy-efficient bulbs, cooking with lids on pots to reduce fuel use, using a solar heater or solar lamp where possible, and choosing to walk or cycle for short distances rather than using motor vehicles. Closing doors and windows while cooling or heating a room prevents loss of energy and makes appliances work less. Keeping appliances in good condition and using them only when needed also saves electricity.

At school, students can save energy by making use of natural daylight instead of switching on lights during the day, turning off projectors and fans when classes finish, arranging classrooms to reduce the need to move items unnecessarily, and using both sides of paper to reduce paper waste (saving energy used to make paper). Teachers should involve students in small energy audits: list classroom appliances, note when they are used, and suggest improvements. Projects like planting trees near the school to reduce heating in summer, or installing a small solar water heater for the lab, teach practical steps to save energy.

Saving energy not only lowers household and school expenses but also reduces smoke and pollution from burning fuels. When children learn to save energy early, they help their families and the community and contribute to a cleaner environment.

This topic connects the ideas of force, work and energy to everyday activities and helps students practise spotting what happens in common tasks. Many normal activities involve forces causing motion and energy changing form. By describing these activities in terms of force, movement and energy, children learn to use scientific words and to see science around them.

Examples to discuss include: climbing stairs requires muscular force and raises your height, increasing your potential energy; running converts chemical energy from food into kinetic energy; boiling water uses heat energy from a stove to increase water temperature and cause steam; and charging a mobile phone stores electrical energy in the battery as chemical energy. In all these activities we can name the force, the movement or change, and the form of energy before and after the action. For instance, when you throw a ball up, your muscles give it an upward force and it gains height (potential energy) and then falls converting this energy into motion (kinetic energy).

Students should practise by choosing one daily activity and writing or drawing its energy story: what gives the energy, what forces act, how things move, and what forms of energy appear at the end. Classroom tasks might include tracing the energy flow in making tea, using a bicycle, or lighting a bulb. Teachers can ask children to present short reports or drawings that show the steps. These exercises strengthen observation, language and reasoning, and prepare students for more detailed study in higher classes.

This final topic brings together key ideas from the unit through short revision and hands-on practical activities. Review the main points: forces are pushes or pulls, work in science needs force plus movement in force direction, energy is the ability to do work, potential energy is stored energy, kinetic energy is energy of motion, energy changes form in many processes, and sources can be renewable or non-renewable. Use practical activities to make these ideas clear and memorable.

Suggested simple activities include: rolling a ball down ramps set at different heights and observing which travels farther to relate height (potential) and motion (kinetic); lifting small weights to different shelf heights to compare effort and see stored energy; stretching different rubber bands and launching paper planes to notice elastic potential energy and motion; rubbing hands or sliding palms on a desk to feel heat produced by friction. Use safe, supervised setups and avoid very heavy loads.

Group tasks strengthen learning: classify classroom objects into those having potential energy and those having kinetic energy, match forms of energy to pictures, and trace energy flow in appliances. Short experiments like using a toy pulley to lift a small weight show how simple machines change effort. Teachers can end with oral quizzes, matching exercises and drawing tasks to check understanding. Encourage students to write one paragraph on how they saved energy at home or school in the last week. These activities help students use vocabulary correctly and recognise energy and work in their everyday lives.