Contact and Non-Contact Forces

Vectors have magnitude and direction

• Force is a vector quantity-vector quantities have a magnitude and a direction
• Lots of physical quantities are vector quantities: force, velocity, displacement, acceleration, momentum,etc
• Some physical quantities only have magnitude and no direction, these are called scalar quantities:speed, distance, mass, temperature, time, etc
• Vectors are usually represented by an arrow-the length of the arrow shows the magnitude and the direction of the arrow shows the direction of the quantity
• Velocity is a vector, but speed is a scalar quantity. Both bikes are travelling at the same speed, but they have different velocities because they are travelling in different directions

Forces can be contact or non-contact

• A force is a push or a pull on an object that is caused by it interacting with something
• All forces are either contact or non-contact forces
• When two objects have to be touching for a force to act, that force is called a contact force
• If the objects do not need to be touching for the force to act, the force is a non-contact force
• When two objects interact, there is a force produced on both objects. An interaction pair is a pair of forces that are equal and opposite and act on two interacting objects(basically Newtons third law)

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Examples:

The sun and the earth are attracted to each other by the gravitational force. This is a non-contact force. An equal but opposite force of attraction is felt by both the sun and earth.

A chair exerts a force on the ground, whilst the ground pushes back at the chair with the same force. Equal but opposite forces are felt by both the chair and the ground

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