Laws of Newton:
The first law states
a body shall continue in a state of rest or of uniform
motion in a straight line unless
impressed upon by a force.
This repeats Galileo’s idea of the natural state of a
and defines the nature of force.
The question of the frame of reference is now raised.
clarify the situation we shall regard
force to be the action of one body upon another. Thus
isolated body will move in a
straight line at constant speed relative to an inertial
frame of reference. This statement could
be regarded as defining an inertial fiame; more
The second law is
the rate of change of momentum is proportional to the
impressed force and takes place
in the same direction as the force.
This defines the magnitude of a force in terms of the
rate of change of the product
of mass and velocity. We need to assume that mass is
measure of the amount of
matter in a body and is tcrbe regarded as constant.
The first two laws &e more in the form of definitions
the third law which states that
to every action cforce) there is an equal and opposite
is a law which can be tested experimentally.
Newton’s law of gravity states that
the gravitational force of attraction between two
one of mass m, and one of
mass m2. separated by a distance d, is proportional to
m,mJd2 and lies along the line
joining the two centres.