Science notes in class 9, Schemes and Mind Maps of Computer science

Download Science notes in class 9 and more Schemes and Mind Maps Computer science in PDF only on Docsity!

Gravitation

Gravitation The Universal Law of Gravitation Free Fall The Value of g Mass and Weight Weight of an Object on the Moon Thrust and Pressure Buoyancy Archimedes’ Principle

Topics to be Covered

A stone tied to a thread moves in a circle due to centripetal force , acting towards the center. Example: Earth's gravity provides the centripetal force for the Moon's orbit. Circular motion involves constant direction change, altering velocity. Centripetal force ensures circular motion, preventing the object from moving straight. The Moon's orbit is maintained by Earth's centripetal force.

Centripetal Force?

“Gravitation or just gravity is the force of attraction between any two

bodies.”

Gravitation

Examples:

The force that causes the ball to come down is known as gravity

Gravity keeps the planets in orbit around the sun.

Gravity is the force that causes a rock to roll downhill.

Lets derive unit for gravitational constant (G):

Q. The Earth is acted upon by the gravitational force of the Sun, even though it does not fall into the Sun. Why? [ 2013, 2017, 2020 ]

Q. How does the force of gravitation between two objects change when the distance between them is reduced to half?

Q. Determine the gravitational force if the mass of two bodies are 80 kg

and 200 kg and they are separated by a distance of 6m.

Importance of the Universal Law of Gravitation:

The force that binds us to the earth. The motion of moon around the earth. The motion of earth around the sun. The tides due to moon in the sea.

The force on an object due to gravity: Equating Forces: Acceleration due to Gravity According to Newton's law of gravitation: G = gravitational constant. M = mass of the Earth. m = mass of the object. R = Earth's radius. { g = acceleration due to gravity }

Variation in Value of (g) Altitude g decreases as you move away from the Earth's surface because the Earth's radius increases. Depth g decreases as you move deeper into the Earth because the Earth's mass decreases faster than its radius. Latitude g is highest at the poles and lowest at the equator because the Earth is not a perfect sphere. The Earth bulges at the equator and flattens at the poles, so the radius is larger at the equator.

Q. Why does a body reach the ground quicker at the poles than at the

equator when dropped from the same height?

Q. A planet whose mass and radius are both half of that of earth.

Acceleration due to gravity(g) at its surface should be:

Difference between ‘G’ and ‘g’ G g Universal Gravitational Constant Acceleration due to gravity It is constant everywhere in the universe. It varies from planet to planet. G = 6.67 X 10⁻¹¹ g = 9.8 m/s² Unit: Nm²/Kg² SI Unit: m/s²