Three laws of motion
Newton's three laws of motion were formulated by Isaac Newton and published in 1687 in the Philosophiae Naturalis Principia Mathematica as the three laws underlying classical mechanics. Newton's laws of motion are also called the ‘laws of motion’ as they define the relationship between the motion of a body and the forces acting upon it.
Formulation of Newton's first law of motion:
Law 1: Newton's first law of motion
Newton's first law of motion is often stated as: an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. This law is often called the law of ‘inertia’.
According to Newton's first law of motion, there is no difference between bodies
- which are at rest, so that no force acts on them, and
- bodies that are moving with constant velocity, so the resultant of these forces is equal to 0.
Example of Newton's first law: a snowball thrown by a child flies by itself or a force of inertia acting on the passengers of a braking or rapidly moving tram (passengers lean back or forward).
Law 2: Newton's second law of motion
If a force or a set of unbalanced forces acts on a body, the body moves with uniformly accelerated motion and the acceleration a is directly proportional to the force (F) and inversely proportional to the body mass (m).
This can be described by the following formula: a = F/m => F = a*m
The above formula allows us to define the unit of force, which was called the ‘newton’ in honour of Isaac Newton. One newton is the force that gives a body of mass 1kg an acceleration of 1m/s2: 1N=1kg⋅1m/s2
Example of Newton's second law: an apple falling freely from a tree.
Law 3: Newton's third law of motion
If body A is acted on by body B with a certain force F1 (called action), then body B acts on body A with a force F2 (called reaction) of the same value, same direction, but opposite direction. In the shortened version, In the shortened version: each action is accompanied by a reaction equal in value and direction but opposite in direction.
Example of Newton's 3rd law of motion: the pull-up bar.
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