Force – an interaction between two bodies or a body and its environment.
In other words a force is a push or a pull. They are vector quantities, having both direction and magnitude and we have many different types.
Contact Forces
A contact force is any force that involves the direct contact of two bodies. For example the force you exert on a door when you push it open. We can break contact forces down into three main types:
Normal Force – a force exerted by a surface onto any object in contact with it.
Normal forces act perpendicular to the surface.
This means that any object experiences an upwards force when in contact with a surface. For example, a book lying on a table experiences a normal force exerted by the table. Or a person stood on the ground experiences a normal force (N) exerted by the ground.
Frictional Force – a force exerted on an object by a surface that opposes the direction of movement.
Frictional forces act parallel to the surface.
For example, when a car travels forwards there is a frictional force between the surface of the road and the tyres of the car. The frictional force (f) acts in the opposite direction to the car and so slows the movement down.
Tension Force – a pulling force exerted by a string or cord on an object.
For example, a light hanging from a ceiling experiences tension from the wire holding it up. The diagram below shows another example of tension (T). The object is being pulled along by a string. As you can see the force is in the direction of the pull, it is important to make sure your arrows are the right way round.
Using this example we can see all three contact forces:
Forces Outside the Nucleus
If we look outside the nucleus of the atom there are three types of force:
Gravitational Force – a force of attraction that acts between two objects with mass.
Electrical Force – an attractive or repulsive force between two charged objects.
Magnetic Force – an attractive or repulsive force between moving charged objects.
The Newton
Forces are measured in Newtons. We can define one newton as follows:
One Newton – the force required to give an object with a mass of 1kg an acceleration of 1ms-2.
From this we can see that 1 N = 1 kg ms-2
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