# WRITE THE THREE LAWS OF GRAVITY

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by PURNACHANDRA
do u want laws of motion of newton ? laws of gravitation of planets ?

2014-11-19T07:19:31+05:30

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The following are knows as laws of Gravitation.  They are mainly for the planetary systems.  These are also known as Kepler's laws.

1.  Every planet moves in an elliptical orbit with the Sun situated at one of the foci.

2.  A planet revolving around the Sun at the focus of the elliptical orbit, sweeps the same areas in the same period of time.

3.  The square of the time period of revolution of a planet is proportional to the cube of the semi-major axis of the ellipse traced out by the planet.

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Newton's Laws of Motion

1st law:    If there is no net external force on an object, then it continues to stay at rest, if it is at rest, and it continues to move with the same speed if it is in motion.  (It continues in the same direction.)

An object continues to be in the state of inertia of rest or uniform motion in a straight line unless compelled by a net external force is acting on it.

If I put a book on a table. the net force acting on it is 0. so it stays there at rest, as it is. A skating person on ice, moves forward with same speed.

2nd law:   The rate of change of momentum is equal to the unbalanced (net or resultant) force acting on a body and takes place in the direction of the force.    OR, equivalently,  the force acting on a body is equal to the product of its mass and acceleration.

3rd law:   If a body1 exerts a force F1 on another body2, then the body to exerts a force - F2 on body1 in the opposite direction.

Two wrestlers exert force F on each other through the hands. Each wrestler is pushed backwards with force - F. But they remain stationary for some time.  How? A wrestler pushes the ground with force -F. The floor pushes him forward with force F. The forces on the wrestler balance and he remains stationary.