Presentation Title

KRISHNA PUBLIC SCHOOLKoni, Bilaspur

Physic ProjectTopic ; Gravitation

Content:Gravitation.Keplers lawUniversal law of gravitation.Force of gravitation on earth & on moon.Acceleration due to gravity.Free fall.Mass & weight .

Gravitation:Movement, or a tendency to move, towards a centre of gravity, as in the falling of bodies to the earth is known as Gravitation .

Gravitational force:The force of attraction between any two particle in the universe is called Gravitation or Gravitational force. For example: moving of planet around the sun in universe or falling of apple from tree toward earth.

Moving of planets around sun in its own axisFalling of apple from tree

Kepler's laws:

Johannes kepler gave the following three law to explain the motion of the planets:Law of orbit: Each planet moves around the sun in an elliptical orbit with the sun at one of the foci*of the orbit.

* Foci is the plural of the term focus.

Sun

2.Law of areas : The line joining the sun and planet sweeps out equal area in equal interval of time. let a planet moves from position A to B in time t and then it moves from position X to position Y in the same time t . Then according to keplers second law, area SAB= area SXY

Universal Law of Gravitation:According to this law, the force of attraction between two Particle or bodies is (i) directly proportional to the product of their masses and (ii) inversely proportional to the square of the distance between these particle or bodies.

Relation between gravitation force between two bodies and the distance between them . Consider two bodies A and B having mass m1 and m2 respectively. Let distance between them be r.

According to the law of gravitation, the force of attraction (F) or force of gravitation between these bodies is directly proportional to :

Video explaining laws of keplers & Universal law of gravitation;

Acceleration due to gravityThe acceleration with which a body falls towards the earth due to earth gravitation pull is known as acceleration due to gravity. It is denoted as g.

Factors on which acceleration due to gravity depends ;Acceleration due to gravity (g) isDirectly proportional to the mass of the earth. And Inversely proportional to the square of the radius of the earth.

Free fall:The falling body of which only which only force of gravitation of the earth acts is known as freely falling body and such fall of a body is known as free fall. A freely falling body has acceleration equal to acceleration due to gravity.

FREE FALL

The picture show freely falling of object.

Mass & WeightMass : Mass of a body is defined as the quantity of matter contained in the body. Since mass of body is a measure of inertia of the body, so mass is also know as Inertia mass. The unit of mass is kilogram (KG)

Weight :

The force with which the body is attracted by the earth is known as the weight of the body.

MASSWeightMass of a body remains constant.Weight of a body changes from place to place.Mass of body is never zero.Weight of a body at the centre of the earth is zero.Mass is a scalar quantity.Weight is a vector quantity.Mass is measured in Kg.Weight is measured in Kg wt. or N.Mass is measured by a beam balance.Weight is measured by a weighing machine or a spring balance.

Difference between Mass & Weight

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Some important Notation:

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