Newton's Laws

Newton’s laws of motion, in other words Newton’s laws, can be grouped under the following headings:

The Principle of Inertia

The first of Newton’s laws is the principle of inertia. Unless an external force acts on an object, that object maintains its previous state. That is, if the object is at rest, it remains at rest; if it is in motion, it continues moving at a constant speed. (The principle of inertia.)

Examples of the Principle of Inertia

When you brake suddenly in a car, your body being thrown forward involuntarily is also an example of Newton’s principle of inertia. This is why seatbelts are used in vehicles.

A catapult system. Released from its spring and suddenly set in motion, the catapult arm hits an obstacle at a certain point and stops. The stone in its cup, however, wants to continue moving and is launched.

Principle of Inertia (1st Law)

An object maintains its state of motion (at rest or constant speed) unless a net force acts on it.

Force-Acceleration Relationship (2nd Law)

The formula F=ma states that the net force applied to an object is directly proportional to its mass and acceleration.

Action-Reaction Principle (3rd Law)

For every action, an equal and opposite reaction force is produced.

The Relationship Between Mass and Acceleration

One of Newton’s laws is also the relationship between mass and acceleration. When a force acts on any object, an acceleration occurs in that object along the direction and orientation of the force. The magnitude of the resulting acceleration is directly proportional to the force and inversely proportional to the mass.

Newton’s 2nd law: the relationship between force, mass, and acceleration F = force (N) / m = mass (kg) / a = acceleration

The Action-Reaction Principle

Another of Newton’s laws is the action-reaction principle. If one object exerts a force on another object, the second object exerts an equal and opposite force back on the first object.
Just as a single force affects objects with different properties in different ways, different forces acting on the same object also produce different motions in that object.

That said, through his experiments, Galileo had discovered the first two of these principles that are attributed to Newton. However, Newton formulated these findings and, by basing his astronomical predictions on these principles, made a fundamental start to the field of dynamics.

Newton’s laws of motion were determined by Isaac Newton after he studied the motions of the stars. Consequently, the laws apply strictly only to material points (point masses).

Since every point of an object is assumed to have the same speed and acceleration, Newton’s laws cannot be applied directly to the motion of extended bodies. However, by considering that objects are made up of a collection of material points, these laws can be extended to apply within objects as well.

Related Questions

Our body “wants” to maintain its previous speed of motion even as the vehicle slows down; this is Newton’s principle of inertia. The vehicle stops, but the body wants to continue moving, which throws us forward.

According to the formula F=ma, acceleration is found by dividing force by mass. As mass decreases, the resulting acceleration under the same force increases; this is why a lighter object accelerates faster under the same push.