We Know – Gravity Sucks
Newton’s laws of motion consist of three physical laws that form the basis for
classical mechanics. They describe the relationship between the forces acting on
a body and its motion due to those forces. They have been expressed in several
different ways over nearly three centuries, and can be summarized as follows:
1. First law: Every body remains in a state of rest or uniform motion (constant
velocity) unless it is acted upon by an external unbalanced force.
This means that in the absence of a non-zero net force, the center of mass of a body
either remains at rest, or moves at a constant speed in a straight line.
2. Second law: A body of mass m subject to a force F undergoes an acceleration
a that has the same direction as the force and a magnitude that is directly
proportional to the force and inversely proportional to the mass, i.e., F = ma.
Alternatively, the total force applied on a body is equal to the time derivative
of linear momentum of the body.
3. Third law: The mutual forces of action and reaction between two bodies
are equal, opposite and collinear. This means that whenever a first body exerts a
force F on a second body, the second body exerts a force −F on the first body.
F and −F are equal in magnitude and opposite in direction. This law is sometimes
referred to as the action-reaction law, with F called the “action” and −F the
“reaction”. The action and the reaction are simultaneous.