Presentation on gravitation for class 9th
- 3. Gravitation. Kepler’s law Universal law of gravitation. Force of gravitation on earth & on moon. Acceleration due to gravity. Free fall. Mass & weight .
- 4. Movement, or a tendency to move, towards a centre of gravity, as in the falling of bodies to the earth is known as Gravitation .
- 5. 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.
- 6. Moving of planets around sun in its own axis Falling of apple from tree
- 7. Johannes kepler gave the following three law to explain the motion of the planets: 1. 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
- 8. 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 kepler’s second law, area SAB= area SXY
- 9. 3. Law of period: The square of time taken by a planet A to complete a revolution around the sun is directly proportional to the cube of semi-major axis of the elliptical orbit i.e., T ∝ r or T = (constant) 𝑟3 or 𝑇2 𝑟3 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
- 10. 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.
- 11. 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 :
- 12. (i) product of masses of bodies i.e., F∝ m1 m2 And, (ii) inversely proportional to square of distance between bodies. i.e., F∝ 𝟏 𝑟2 Combining eqns. (1)&(2),we get F∝ m1 m2 𝑟2 Or F=G m1 m2 𝑟2 G is constant and is known as Universal Gravitation Constant
- 14. The 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’.
- 15. Acceleration due to gravity (g) is i. Directly proportional to the mass of the earth. And ii. Inversely proportional to the square of the radius of the earth.
- 16. 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.
- 17. The picture show freely falling of object.
- 18. Mass : ass 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)
- 19. Weight : T h e f o r c e w i t h w h i c h t h e b o d y i s a t t r a c t e d b y t h e e a r t h i s k n o w n a s t h e w e i g h t o f t h e b o d y .
- 20. MASS Weight Mass 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.
- 21. Radius of earth = 6.4x106 m Mass of earth = 5.98x1024 Kg G = gravitational constant; 6.673x10-11 Nm2 / sec2 g = acceleration due to gravity=29.8m/sec2 acceleration (g) on the moon=> gmoon= 1 6 𝑔 𝑒𝑎𝑟𝑡ℎ.