Types of forces

In a nutshell

Most forces are applied by contact, these forces can either be pushes or pulls. When a force acts on an object, it can make an object change the way it is moving or even the shape of the object. Forces are measured in Newtons ($$N$$​).
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Forces on objects

A force can change the way an object is moving, it can slow down or speed up a moving object. If an object is not moving, a force can make the object start moving. Forces can also cause an object to change shape. By applying a force in the opposite direction, these effects can be reduced. 

A simple way to think of forces is pushing and pulling. If something moves away, it is a push. If something moves towards you, it is a pull.

Types of forces

Whenever there is a moving object, it must have forces acting on it. These forces can be either non-contact and contact.

Non-contact forces

A non-contact force is one which objects do not need to touch in order to feel its affect.

Gravitational, magnetic and electrostatic are non-contact forces.

Example

When an object is falling, the force of gravity from the Earth is acting on the object and this is why it falls towards the ground. You don't need to be to be touching the ground to feel the force of gravity.

Contact forces

A contact force is one which objects need to be touching in order to feel its affect.

Friction, air resistance and water resistance are all contact forces and act in the opposite direction to the one that the object is moving in. These forces slow down the moving object. 

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Example

When an object is falling through the air, there is a resistive force of air resistance. The air and the ball are touching, which makes it a contact force.

Contact and non-contact forces can happen at the same time, and can act in opposite directions to each other.

The diagram below shows a falling ball which has both a contact (air resistance) and a non-contact force (weight due to gravity) acting upon it.  

1. Air resistance 2. Weight due to the force of gravity

Force arrows

Forces can be represented using arrows. Force arrows point in the direction the force is acting and its length represents the size of the force. A longer arrow means a larger force. 

Example

A block dropped in a beaker of water has the force of its weight acting downwards and the force of upthrust acting upwards.  The block will sink because the force of weight is greater (shown by a longer arrow) than the upthrust.

1. Upthrust 2. Weight

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