Force can be defined as any action that moves or tries to move a body or alter its speed in a given direction.

Force is that action which changes the position and shape of a body. It has the following effects on a body. It:

1. Changes the shape of a body

2. Makes a body at rest to move

3. Makes a moving object stop

4. Causes an object to change its direction

5. Causes a body to change its speed.


There are two types of force. These are contact and non-contact forces.


A contact force exists between two or more surfaces when the source of the force is in contact with the body it is acting upon. For example, when people are pushing a car, they place their hands on the car and push.

Contact force can be direct or indirect. Examples of direct contact force are push, pull, lift and friction while an example of indirect contact force is tension.

1. Push: This is a force that comes behind a body and moves it forward, opposite to the source of the force. E.g. pushing a car, a cart, etc.

2. Pull: This is a force that draws a body towards the source of force e.g. pulling a door, pulling a bucket of water from the well, etc.

3. Tension: This is force on a stretched body e.g. stretched wire, spring, rubber band, bent rod, etc.

4. Friction: This is the force that opposes relative motion between two surfaces that are in contact with each other. Friction is greater when the surfaces of the body in contact are rough than when they are smooth.

Advantages of Friction

1. Walking: One can walk on the ground easily because there is friction between one’s feet and the ground. It is difficult to walk on wet slippery ground, tiled polished floor and plastic carpet because of low friction. Rough surfaces like rough cement floors have high frictional force; therefore, they are not slippery and are easy to walk on.

2. Vehicles: Friction makes a moving vehicle to come to a stop whenever its brakes are applied. Also, the tyres of cars have rough surfaces so that they can grip on the surface of the road well. The grip of the tyre on the road allows the car to move without skidding or slipping off the road. This is caused by friction between the tyre and the road.

3. Grindstone: A cutlass or knife can be sharpened by the use of a grindstone. The friction between the grindstone and these tools will allow these tools to be sharpened.

Disadvantages of Friction

Friction can be very useful but if care is not taken, it can become a nuisance.

1. Wear and tear of machines: Friction causes wear on the moving parts of machines. The surfaces of machines get hot when they are running over each other causing unpleasant noise at times.

2. Reduction of efficiency: Much work is done to overcome friction in a machine. For example, if a wheel is to be rotated by a force of 10N, because of friction, the wheel may be rotated by an extra force of 6N, which could have been used for another thing.

Methods of Reducing Friction

1. Lubrication: To prevent metal-to-metal contact in a machine, the surfaces in contact are rubbed with oil or grease. The lubricants allow for slippery movement of machine parts.

2. Use of ball-bearings or rollers: Ball bearings are small metal balls which can allow a part of a machine to run easily with less rubbing. Therefore, ball bearings and rollers help reduce friction. A trolley moves easily because of the rollers under it.