Common forces – types, definition & examples

In this post, we will discuss 8 common forces we find in Physics. For every such force type, we will find out the cause or reason or source of the force and also will site a few examples.

The common forces we include are (1) weight, (2) Normal contact or normal force, (3) Friction, (4) Air/water resistance, (5) Upthrust, (6) Electrostatic forces, (7) Magnetic forces & (8) Strong and weak nuclear forces.

8 common forces we discuss in Physics

Here we list down the details of the forces.

Weight

Weight is the gravitational force of attraction acting on one object by another object’s mass.

This is usually the downwards force on an object caused by the mass of the Earth.

There is a gravitational attraction between any two masses but it is normally too small to measure.

Can also be called the force due to gravity.

Examples: An object in freefall, The downwards force on an object sitting on a surface

Normal contact or normal force

Normal contact or normal force – This is the force that acts on an object caused by any object that is supporting it.

It is sometimes referred to as a support force.

Examples: Someone standing on the floor, Sitting on a cushion

Friction

Friction – This is a force that opposes motion or attempted motion. There is still a friction force acting on something that is stationary but being pushed.

This force always acts in the opposite direction to the movement or potential movement.

Examples: A wardrobe being pushed across a floor, The horizontal force between bicycle tires, and a flat road

Air/water resistance

Air/water resistance – When there is movement between a solid and fluid (liquid or gas) then there is a particular type of friction between them, also known as drag.

Unlike the friction on a sliding object which remains constant, this force increases with the speed of the object and is always in the opposite direction to the motion.

Examples: A fish swimming, A dropped brick that is falling down

Upthrust

Upthrust is the upwards force on an object in a fluid (liquid or gas).

Most examples will involve objects floating in liquids, but it is important to note that there is an upthrust in all fluids and even if the object is sinking. Things sink because the upthrust is less than the weight.

Examples: A block of wax floating in the water, A helium balloon floating in the air

Electrostatic forces

Electrostatic forces are the non-contact forces between any charged objects. These often act on a submicroscopic scale, acting between molecules to keep structures together.

Examples: A charged balloon sticking to a wall

Magnetic forces

Magnetic forces – These non-contact forces act between:
• magnets
• magnets and magnetic materials
• charged particles moving in a magnetic field.

Examples: Two magnets repelling or attracting, A fridge magnet holding a note on the fridge door

Strong and weak nuclear forces

Strong and weak nuclear forces – These forces act between and within subatomic particles and only act over very small distances.

Examples: The force within the nucleus of an atom that holds matter together (strong) and the force involved in beta decay (weak)