# Gravitation Class 9 Notes Science - Chapter 10

## Chapter: 10

## What Are Gravitation ?

## Gravitation

Force between two objects or bodies which attract each other due to their masses

**Effects of Gravity**

**Free fall**

• When an object falls down towards the earth under the gravitational force only.

• Velocity of free falling body changes and is said to be acceleration due to gravity.

^{2}. Value of g = 9.8 m/s

^{2}.

**Equation of Motion**

• v = u + gt

^{2}

^{2}– u

^{2}= 2gh

^{2}

- When a body is projected vertically upward with an initial velocity, u, than g = –9.8 m/s
^{2}

**Acceleration due to gravity**

• It is the gravitational attraction of earth

^{2}

**Universal Law of Gravitation**

- It states that every object in the universe attracts every other object with a force which is proportional to the product of their masses and inversely proportional to the square of the distance only.

- F∝(Mm/d
^{2})

^{2}) [ ∵ G = Universal gravitational constant]

^{2}/Kg

^{2}

^{–11}Nm

^{2}/Kg

^{2}

## Relation Between g And G

^{2})

M = Mass of the earth

R = Radius of the earth)

^{-11}Nm

^{2}Kg

^{–2}×6 × 10

^{24}Kg/(6.4 × 10

^{–6}m)

^{2})

• As the radium of the earth increases from the poles to the equator, the value of g becomes greater at the poles than at the equator.

## Mass And Weight

**Mass**

• Mass of an object is the measure of its inertia. (Scaler quantity)

• It remains the same everywhere in the Universe.

• SI Unit : Kg

**Weight**

• Weight is the force of attraction of the earth on the object (vector quantity)

• Weight of the body changes form place to place

• W = mg

• SI Unit: Newton (N)

## Thrust

• Net force applied in a particular direction.

• Depends on the area on which it acts.

• SI Unit: Newton

**Archimedes’ Principle**

When a body is immersed fully or partially in a field, it experiences an upward force that is equal to the weight of the fluid displaced by it.

**Applications:**

• Used in designing ships and submarines

• Used in lactomoters to find purity of milk.

• Used in hydrometer to determine density of liquid.

## Upthrust

• When an object is immersed in a fluid, they experience a buoyant force.

• Depends on the density of the fluid.

• Upward force entered by liquid on a body.

• Density of object < density of liquid ⇒ object floats.

• Density of object > density of liquid ⇒ object sinks.

## Pressure

• Force per unit area

• P =(F/A)

• Pressure =(Thrust/Area)

^{2}or Pascal