Every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed on it.

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Every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed on it.

"Every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed on it."

"Force is equal to the change in momentum(mV) per change in time. For a constant mass, force equals mass times acceleration."

"For every action, there is an equal and opposite re-action."

$F$, Symbol for Force(in Newtons);

$m$, Symbol for Mass(in Kilograms);

$a$, Symbol for Acceleration(in Meter per second per seconds);

${F}_{grav}$, Symbol for Weight(in Newtons);

$g$, Symbol for The acceleration of gravity(Approximately 9.8 ms^{-2} for Earth. );

$V$, Symbol for Velocity(in Meter per seconds);

$t$, Symbol for Time(in Seconds);

${F}_{frict}$, Symbol for Friction(in Newtons);

$\mu $, Symbol for The coefficient of friction;

${F}_{n}$, Symbol for Applied force to the surface(in Newtons);

The empirical laws of Kepler describe planetary motion, but Kepler made no attempt to define or constrain the underlying physical processes governing the motion. It was Isaac Newton who accomplished that feat in the late 17th century. Newton defined momentum as being proportional to velocity with the constant of proportionality being defined as mass. (As described earlier, momentum is a vector quantity in the sense that the direction of motion as well as the magnitude is included in the definition.) Newton then defined force (also a vector quantity) in terms of its effect on moving objects and in the process formulated his three laws of motion: (1) The momentum of an object is constant unless an outside force acts on the object; this means that any object either remains at rest or continues uniform motion in a straight line unless acted on by a force. (2) The time rate of change of the momentum of an object is equal to the force acting on the object. (3) For every action (force) there is an equal and opposite reaction (force). The first law is seen to be a special case of the second law. Galileo, the great Italian contemporary of Kepler who adopted the Copernican point of view and promoted it vigorously, anticipated Newton’s first two laws with his experiments in mechanics. But it was Newton who defined them precisely, established the basis of classical mechanics, and set the stage for its application as celestial mechanics to the motions of bodies in space. According to the second law, a force must be acting on a planet to cause its path to curve toward the Sun. Newton and others noted that the acceleration of a body in uniform circular motion must be directed toward the centre of the circle; furthermore, if several objects were in circular motion around the same centre at various separations r and their periods of revolution varied as r3/2, as Kepler’s third law indicated for the planets, then the acceleration—and thus, by Newton’s second law, the force as well—must vary as 1/r2. By assuming this attractive force between point masses, Newton showed that a spherically symmetric mass distribution attracted a second body outside the sphere as if all the spherically distributed mass were contained in a point at the centre of the sphere. Thus, the attraction of the planets by the Sun was the same as the gravitational force attracting objects to Earth. Newton further concluded that the force of attraction between two massive bodies was proportional to the inverse square of their separation and to the product of their masses, known as the law of universal gravitation. Kepler’s laws are derivable from Newton’s laws of motion with a central force of gravity varying as 1/r2 from a fixed point, and Newton’s law of gravity is derivable from Kepler’s laws if one assumes Newton’s laws of motion.

$F=m\times a$

${F}_{grav}=m\times g$

$F=\frac{{m}_{1}{V}_{1}-{m}_{0}{V}_{0}}{{t}_{1}-{t}_{0}}$

$F=m\frac{{V}_{1}-{V}_{0}}{{t}_{1}-{t}_{0}}$

${F}_{frict}=\mu \times {F}_{n}$