THE THREE LAWS

1. First Law: Tis law is often simplified into the sentence "A particle will stay at rest or continue at a constant velocity unless acted upon by an external unbalanced force"

2. Second law: This law is often stated as "F = ma: the net force on an object is equal to the mass of the object multiplied by its acceleration."

3.Third law: This law is often simplified into the sentence "Every action has an equal and opposite reaction."

Newton's first Law: Law of Inertia

Essentially, it makes the following two points:

• An object that is not moving will not move until a net force acts upon it.


• An object that is in motion will not change its velocity (accelerate) until a net force acts upon it.

Newton's second Law: Law of resultant Force

Using modern symbolic notation, Newton's second law can be written as a vector differential equation:

where:

is mass

is the velocity vector

is time.

The product of the mass and velocity is the momentum of the object (which Newton himself called "quantity of motion"). Therefore, this equation expresses the physical relationship between force and momentum for systems of constant mass. The equation implies that, under zero net force, the momentum of a system is constant; however, any mass that enters or leaves the system will cause a change in system momentum that is not the result of an external force.

It should be noted that, as is consistent with the law of inertia, the time derivative of the momentum is non-zero when the momentum changes direction, even if there is no change in its magnitude. See time derivative.

Since the mass of the system is treated as constant this differential equation can be rewritten in its simpler and more familiar form:

where:

is the acceleration.

A verbal equivalent of this is "the acceleration of an object is proportional to the force applied, and inversely proportional to the mass of the object". If momentum varies nonlinearly with velocity (as it does for high velocities—see special relativity), then this last version is not accurate.

Newton's third Law: Law of recIprocal actions

In other words "For every action there is an equal, but opposite, reaction".

The Third Law means that all forces are interactions - that there is no such thing as a unidirectional force. If body A exerts a force on body B, simultaneously, body B exerts a force of the same magnitude body A, both forces acting along the same line. As shown in the diagram opposite, the skaters' forces on each other are equal in magnitude, and opposite in direction. Although the forces are equal, the accelerations are not: the less massive skater will have a greater acceleration due to Newton's second law. It is important to note that the action/reaction pair act on different objects and do not cancel each other out. The two forces in Newton's third law are of the same type, e.g., if the road exerts a forward frictional force on an accelerating car's tires, then it is also a frictional force that Newton's third law predicts for the tires pushing backward.

NEWTON LAWS

Biography Newton

Isaac Newton 4 January 1643 – 31 March 1727

• Was an English physicist, mathematician, astronomer, natural philosopher, alchemist and theologian.
  
• His Philosophiæ Naturalis Principia Mathematica, published in 1687, is considered to be the most influential book in the history of science. In this work, Newton described universal gravitation and the three laws of motion, laying the groundwork for classical mechanics, which dominated the scientific view of the physical universe for the next three centuries and is the basis for modern engineering.

• Newton showed that the motions of objects on Earth and of celestial bodies are governed by the same set of natural laws by demonstrating the consistency between Kepler's laws of planetary motion and his theory of gravitation, thus removing the last doubts about heliocentrism and advancing the scientific revolution.
• In mechanics, Newton enunciated the principles of conservation of momentum and angular momentum. In optics, he invented the reflecting telescope and developed a theory of colour based on the observation taht a prism decomposes white light into a visible spectrum. He also formulated an empirical law of cooling and studied the speed of sound.
• In mathematics, Newton shares the credit with Gottfried Leibniz for the development of the differential, and integral calculus. He also demonstrated the generalised binomial theorem, developed the so-called "Newton's method" for approximating the zeroes of a function, and contributed to the study of power series.
• In a 2005 poll of the Royal Society asking who had the greater effect on the history of science, Newton was deemed much more influential than Albert Einstein.