A Force can be seen as a Push, a Pull, or a Twist.

A Force can change the Shape, Speed or direction of an Object.

A Force has the Units of Newtons.

Measuring Forces

A Force is measured with a Newton-Balance. A Newton Balance consists of a spring with an attached scale. As Force is applied, the spring is extended:-

Balanced Forces

When two identical Forces act in opposite directions, they cancel each other out. If the object is stationary to begin with, the object will not move:-

Balanced Horizontal Forces

Balanced Vertical Forces

If the object is moving with balanced Forces acting on it, the object will travel at a constant speed:-

Newton's First Law

The above understanding of Forces allowed Isaac Newton to develop the 1st of his three laws of Forces:-

"An object will remain at rest or travel in a straight line with a constant speed, unless an unbalanced Force acts upon it"

Unbalanced Forces

When an object experiences an unbalanced Force, the object will accelerate. This can either be caused by only one Force acting, or by two unequal Forces acting in opposite directions.

In the above diagram, the engine Force acting upwards is larger than the Weight acting downwards, causing the shuttle to accelerate in the upwards direction.

Newton's Second Law

The above understanding of Forces allowed Isaac Newton to develop the 2nd of his three laws of Forces:-

"An unbalanced Force acting on an Object will cause the Object to Accelerate. The size of that acceleration will depend on the size of the Force and the mass of the Object."

The above Law is more commonly described as the formula below :-

F = m x a

Where :-

F = Unbalanced Force (N)

m = Mass of Object (kg)

a = Acceleration of Object (ms−2)

Example 1

A truck of mass 2000 kg is acted upon by two Forces as shown in the diagram below:-

Calculate :-

1. The unbalanced Force acting on the object.

2. The Acceleration experienced by the object.

Unbalanced Force = 50000 - 45000

= 5000 N (to the right)

F = 5000 N

m = 2000 kg

a = ?

F = m x a

a = F / m

a = 5000 / 2000

a = 2.5 m s−2