Forces all around us
What is a force? It is a push or a pull. You cannot see a force but you can see its effects and sometimes feel them. The first force you may be aware of in the morning is the pull of the muscles on your eyelids! You may also be aware of how soft and comfortable the bed feels as your weight pushes down on the mattress. Inside the mattress the coiled springs push back with a force which matches your weight. If they didn't, you would sink to the floor.

When you get up other muscles begin to work. They pull on the bones in your skeleton to move your arms, legs and eventually your whole body. As you walk across the bedroom floor your feet push downwards and backwards on the carpet. A force called friction pushes on your foot to stop it slipping and you move towards the bedroom door.

After you have washed and dressed, you may comb your hair. As the teeth of the plastic comb rub against your hair, tiny particles called electrons pass from your hair to the comb. This gives the comb an electric charge, which produces a force into the air around it. If your hair is long, the force made by the electrical charge pulls your hair upwards and makes it stand on end.

When you go to the kitchen for breakfast, you may encounter another kind of force, which works through the air in the same way as the force of the electrical charge. You will find this force at work in the door of a fridge. In the edge of the door is a magnet. It exerts a pulling force on the steel in the door frame of the fridge and holds the door closed. You pull against this force when you open the fridge door. If you shut the door gently you may feel the magnet pull the door shut.

If you have taken butter out of the fridge you may use a force in another way. When you have placed a lump of butter on your toast or bread, you use this force to spread the butter out. This is an example of a force which is used to change the shape of something.
While you are having your breakfast you may watch television and see a news programme. After this, there may be a sports report and it is here that you can see other examples of what forces can do. If there is a report of a football match you may see forces act in four ways. A player taking a throw in uses a pushing force to make an object (the ball) move. As the ball falls to the ground and rolls along the grass another player kicks across the pitch. This is an example of a force being used to increase the speed of an object. The ball rises into the air then falls and bounces. As the ball rises from the bounce a third player kicks the ball strongly towards the goal. This is an example of a force changing the direction of a moving object. Finally, as the ball shoots towards the goal, the goalkeeper jumps up and catches it. The save is an example of a force stopping a moving object.

There are forces at work all around you all the time. Just sit back in your chair and think about the forces at work around you at this moment. First, you should be able to feel yourself pushing into the seat of the chair. This is due to your weight pushing downwards. A second force is made by the chair which pushes upwards to stop you sinking to the ground. Next you should see that, in a similar way, the weight of your computer is being balanced by the force of the table pushing upwards. If you look outside you may see the pushing force of the wind on trees or bushes. You may also see cars and buses being moved along by the pushing forces of their engines and wheels. When you have finished thinking about forces, pull your mouse to make the cursor reach the scroll bar, then push down to click on the mouse and make the text move on.

When we sit down or lie down why is there a force pushing upwards against our weight?
A force does not exist on its own. There is always a pair of forces. If there was just the force of gravity pulling down on your body you would travel to where the pull is directed - that is the centre of the Earth. The pull of gravity is opposed by the pushing upwards of the chair or bed and the ground on which they stand.

How can the ground, chair or bed make a force against gravity?
They are all solids. A solid is one of the three kinds of matter. All matter is made up from tiny particles. In the solid the particles are held firmly together by forces. This gives the solid the strength to make a force, which opposes the pull of gravity.

What are the particles from which solids are made?
All matter is made from particles called atoms. These can join together into groups called molecules. Some substances are simply made from huge numbers of one kind of atom all joined together. For example, a piece of iron is made from iron atoms. Other substances are made from different atoms joined together to make molecules. For example, water is made from molecules, which contain two hydrogen atoms and one oxygen atom.

Are forces at work to hold liquids, like water, together?
Yes. The forces are not as strong as those that hold solids together. They keep the particles close together but allow the particles to slide over each other.

Do forces hold particles together in a gas?
No. There are no forces to hold the particles together. The particles are free to move away from each other.

What kind of particle is an electron?
After scientists discovered that all matter was made from atoms, they then discovered that atoms were also made of particles. In the centre of an atom is a structure called the nucleus. In it are particles called protons and neutrons. They have forces, which hold them together. Around the nucleus are electrons. They move around the nucleus at very high speeds but are held in place by electrical forces similar to the one that makes combed hair stand on end. When hair is combed only a few electrons in the atoms of molecules in the hair move to atoms of molecules in the plastic comb.

Are gravity and the electrical and magnetic forces different from other forces?
Yes, they are. They are called non-contact forces. The force of gravity is exerted by the Earth on everything around it but it does not have to touch them. If you jump in the air you are not in touch with the Earth but its gravity still pulls you back. A magnet can pull on a paper clip without touching it and an electrically charged comb can pull on hair without touching it.

What are other forces called?
They are called contact forces. These forces are exerted by one object of substance on another. For example an impact force occurs when you kick a ball; friction occurs between your shoes and the ground as you move; air pushes on your face as you ride your bicycle fast; water pushes on you when you dive into a swimming pool.

When a rocket moves through the air do the hot gases push on the air to make the rocket move?
No. In a rocket engine fuel is burnt to make very hot gases. They expand and push on the inside of the engine. There is an opening at the back of the engine. When the gases push here there is no engine wall to contain them, so they shoot out at the back of the engine. This force which pushes the gases out, is balanced by a force generated by the gas that did not escape, which pushes the rocket forwards. If the hot gases pushed on the air to make the rocket move, the rocket could not work in space where there is no air. Rockets work just as well in space as in air because air is not needed for the gases to push against.