Gravitation

Introduction

     we are going to identify one of the forces which produces acceleration in all objects on the surface of the Earth irrespective of their mass.

Force of Gravitation

     The orbit of a planet is an ellipse with the Sun at the one of the foci.The line joining the planet and the Sun sweeps equal areas in equal intervals of time.

The Universal Law of Gravitation or Newton's Law of Gravitation

     Sir Issac Newton gave a mathematical relation to calculate the force of gravitation and this relation is known as the universal law of gravitation.

Dependence of Gravitational Force on Mass

     Newton's law of gravitation, the force of attraction is directly proportional to the mass of the body.

Gravitational Force between two Light Objects

     Gravitational force between two objects of ordinary size is very small, while the force is very large when atleast one of the objects is massive.

Newton's Third Law of Motion and Force of Gravitation

     whenever a force is acting on an object, it produces acceleration in it. The gravitational force of attraction produces acceleration both in the Earth and in the stone.

Falling Objects and Acceleration due to Gravity

     The objects which move towards the Earth due to force of gravity are called freely falling objects.

Expression for Acceleration due to Gravity

     The acceleration produced in a body moving against gravity is also 9.8 m/s2 but oppositely directed therefore g = - 9.8 m/s2.

Equations of Motion for a Body Moving under Gravity

     The motion of a body under gravity is a uniformly accelerated motion and hence all the equations of motion for uniformly accelerated motion along a straight line is applicable to the motion of bodies under gravity.

Acceleration due to Gravity on Moon

     The acceleration produced in any body due to the gravitational pull of the Earth does not depend on the mass of the body.

Mass and Weight

     Mass and weight are commonly mistaken as the same, but they are two different quantities.

Weightlessness

     A body becomes conscious of the weight, whenever its weight is opposed by some other object.

Density

     The density of a substance remains the same under certain specified conditions. Thus the density of a substance is one of its characteristic properties and this property can be used to determine the purity of any substance.

Relative Density of a Substance

     The density of a substance or an object, we find out the mass and volume of the substance.

Thrust and Pressure

     We have defined the force as an external agent, which changes the direction of motion, speed or shape of the body. All along we were discussing only about the forces acting at a point on a body.

Buoyancy and Archimedes' Principle

     It is a matter of common experience that bodies appear lighter when immersed in water or any other liquid.

Summary

     Is the object which moves towards the Earth due to force of gravity.

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