Contact and Non-Contact Forces

Forces can be divided into contact and non-contact. When a force is applied, it can alter an object’s direction, speed, and shape.

Contact Forces

A contact force is a force that requires contact to act on an object.

Below are examples of contact forces:

Reaction Forces

A reaction force, also known as a normal contact force, is exerted in response to an action force but in the opposite direction, leading to the common phrase ‘An equal and opposite force

For example, a book on a table experiences a reaction force from the table.

The book on the table is exerting a downward force on the table, while the table is exerting an upward reaction force on the book. These forces are equal and opposite, so the book remains at rest.

Tension

Tension is a pulling force that stretches an object. For example, in tug of war, two people or groups pull the rope in opposite directions.

Friction

Friction is the resistance of motion when two objects slide over each other. Skateboarding is an example of this.

There will be friction between the wheels of the skateboard and the ground.

Air Resistance

A frictional force that occurs between air and an object. An example of air resistance is with a moving car.

When a car moves, the air surrounding it forms a resistance in the opposite direction to the movement of the car.

Non-Contact Forces

A non-contact force is a force that acts on an object without physically touching it. We can also describe non-contact forces as fields of influence around an object.

There are many types of non-contact forces. Three examples of non-contact forces are:

  • Magnetic
  • Gravitational
  • Electrostatic

Magnetic

Magnetic forces are forces that can attract or repel other magnetic materials in a magnetic field.

Gravitational

Gravity is a force that attracts all objects with mass towards each other.

This force becomes especially noticeable with large bodies, such as planets, because the greater an object’s mass, the stronger its gravitational force. The gravitational force pulls objects inward, towards the centre. This is why on Earth we are pulled towards the ground.

Electrostatic

Electrostatic forces occur between two charged objects.

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