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Last updated on August 24, 2021 2 min read

title: ‘Physics: Newton’’s Laws of Motion’ comments: true categories:

First Law: Inertia

An object in motion will stay in motion, and will maintain its speed and direction, unless acted on by an unbalanced force

The principle of INERTIA is that all objects have a tendency to resist change in motion.
An object with all forces balanced out will not change speed or direction until another force is applied to it.
- For example, a person sitting on a chair is being pulled down by gravity, but pushed up with an equal NORMAL FORCE. The person does not change speed or direction.
- If the person in the above example is in a moving car, which suddenly brakes, the person will continue to move forward until they are stopped by the seat in front of them: the person resists any change in motion until acted on by an external force (the seat in front)
A more massive object therefore needs more force to reach the same acceleration as a less massive object.

Force is equal to mass times acceleration

This is expressed mathematically as \(F=ma\)
- F: Force in Newtons (N)
- m: Mass in Kilograms (kg)
- a: Acceleration in Meters per Second squared \(m/s^2\)

Every Action has an Equal but Opposite Reaction

The reaction force is known as the NORMAL FORCE
The Normal force always acts perpendicular (at \(90^\circ\)) to the surface that your object is on
The Normal force changes magnitude based on the force that it is attempting to balance