Newton's First Law

If the resultant force acting on an object is zero and:
- the object is stationary, the object remains stationary
- the object is moving, the object continues to move at the same speed and in the same direction. So the object continues to move at the same velocity.

So, when a vehicle travels at a steady speed the resistive forces balance the driving force.

So, the velocity (speed and/or direction) of an object will only change if a resultant force is acting on the object.

Students should be able to apply Newton’s First Law to explain the motion of objects moving with a uniform velocity and objects where the speed and/or direction changes.

The tendency of objects to continue in their state of rest or of uniform motion is called inertia.

Newton's Second Law

The acceleration of an object is proportional to the resultant force acting on the object, and inversely proportional to the mass of the object.

As an equation:

\(\text{resultant force} = \text{mass} × \text{acceleration} \)

\(F = m a\)

force, F, in newtons, N
mass, m, in kilograms, kg
acceleration, a, in metres per second squared, m/s²

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Students should be able to explain that:
- inertial mass is a measure of how difficult it is to change the velocity of an object
- inertial mass is defined as the ratio of force over acceleration.

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Students should be able to estimate the speed, accelerations and forces involved in large accelerations for everyday road transport.

Students should recognise and be able to use the symbol that indicates an approximate value or approximate answer, ~

Newton's Third Law

Whenever two objects interact, the forces they exert on each other are equal and opposite.

Students should be able to apply Newton’s Third Law to examples of equilibrium situations.