What is a force?

Every time you open a door, kick a football or pull your school bag onto your shoulder, you are using a force. A force is simply a push or a pull. When you push, the object moves away from you; when you pull, it comes towards you. We cannot see a force itself, but we can always see what it does.

What can a force do?

• Make a still object start moving, like pushing a swing.
• Make a moving object go faster or slower, like pedalling harder or braking on a cycle.
• Stop a moving object, like a goalkeeper catching a ball.
• Change the direction of a moving object, like a batter hitting a cricket ball.
• Change the shape of an object, like pressing dough into a flat roti.

Kinds of force

Some forces, like muscular force and friction, need touch. Others, like gravity and magnetic force, can act from a distance.

What is work?

In everyday life we call homework or housework "work". In science, the word has a special meaning: work is done only when a force makes an object move. Pushing a cart along the road is work. Pushing hard against a wall that does not move is not work in science, even if it makes you tired!

Simple machines make work easier

People have invented simple machines to do work with less effort. A lever, such as a see-saw or a bottle opener, helps lift or open things. A pulley helps raise a bucket from a well or a flag up a pole. A ramp (inclined plane) lets us push heavy loads up instead of lifting them, and a wheel makes carrying loads much easier.

What is energy?

Energy is the ability to do work. We need energy to run, think, grow and keep warm, and machines need energy to run. Energy comes in many forms:

• Heat energy from the Sun, fire and stoves.
• Light energy from the Sun, bulbs and torches.
• Sound energy from drums, bells and voices.
• Electrical energy that runs fans, televisions and computers.
• Chemical energy stored in food, fuels and cells.
• Energy of motion in moving things, and stored energy in a stretched rubber band or water held high in a tank.

Energy changes form

Energy is never used up out of nowhere; it changes from one form to another. A torch changes chemical energy in its cells into light. A fan changes electrical energy into movement. Our body changes the chemical energy in food into movement and heat. Almost all of this energy first came from the Sun, which plants capture to make food.

Sources of energy

Some sources, such as sunlight, wind and flowing water, will never run out. They are called renewable sources. Others, such as coal, petrol and diesel, took millions of years to form and will one day run out. These are non-renewable sources, and burning them also makes smoke that pollutes the air. That is why it is important to save energy: switch off lights and fans when you leave a room, walk or cycle for short trips, and use sunlight whenever you can.

This Force, Work and Energy worksheet for Class 4 turns these ideas into an island adventure on WitKnowLearn with an online quiz, online activities and interactive games. Flip the cards, test pushes and pulls in the Force Lab, play the games, do the science labs, take the challenges and then build a circuit and test friction in the Virtual Lab.