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Gravitation

Gravitation. Standard 9. Gravitation. Is the force pull objects towards the ground is the same that keeps the moon moving around the earth?. Newton’s hypothesis. Just pushed over the table with force F 1. Distance d 1.

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Gravitation

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  1. Gravitation Standard 9

  2. Gravitation Is the force pull objects towards the ground is the same that keeps the moon moving around the earth?

  3. Newton’s hypothesis Just pushed over the table with force F1 Distance d1 When you gently push the ball over the table, it drops more or less near the edge of the table covering very little horizontal distance.

  4. Newton’s hypothesis Pushed with more force F2 Just pushed over the table with force F1 Distance d1 Distance d2 If you push the ball harder (i.e. apply more force) the ball travels a longer distance horizontally before reaching the ground.

  5. Newton’s hypothesis If one could push the ball so hard that the earth always curves off before the ball reaches the ground then the ball would orbit earth like the moon.

  6. Galileo’s Experiment Galileo believed that the time taken by an object to fall to the earth is independent of its mass. He demonstrated this by dropping two objects of different sizes and weights from the Tower of Pisa and calculating the time required by them to reach the ground. It was found that the time taken by the objects is same. This meant that the acceleration of all the bodies because of the pull of the earth was also the same. Since a is constant;

  7. Galileo’s Experiment However when we do the experiment we find that lighter objects take more time to reach the ground. We also find a small variation in the time taken by the same object each time we do the experiment. Why do our answers not match with what Galileo’s observations? Mistakes made by us while noting down the time – Human error Effect of the resistance of air to the motion of an object

  8. Does Gravitational Force depend on distance? Radius of earth = r km 6000000 m Radius of moon’s orbit 60r m Average speed of moon (v) 1000 m/s Acceleration due to gravity on the surface of earth 10 m/s2 = = = =

  9. Factors influencing Gravitation Force G is called the Universal Gravitation constant. G = 6.7 10-11 N m2/ kg2

  10. Universal Law of Gravitation Every object in the universe attracts every other object with a force that is proportional to the product of their masses and inversely proportional to the distance between them. Distance r Mass = M Mass = m

  11. Does the apple also pull the earth? But the mass of the earth (6*1024 kg) is very large and hence its acceleration is extremely small and hence we don’t notice it moving towards the apple.

  12. Acceleration due to Gravity The acceleration produced on an object because of the gravitational force is known as acceleration due to gravity (g). The acceleration due to gravity due to an object depends on the mass of the object and the distance from that object.

  13. Gravity on the surface of earth Radius of earth = r km 6400000 m Mass of earth 6 * 1024 kg

  14. Earth’s gravity with distance As you go deeper, gravity first increases and then decreases In Space gravity decreases exponentially with distance

  15. Gravity on surface of Jupiter Radius of Jupiter 11 times the radius of Earth. Mass of Jupiter 319 times the mass of Earth.

  16. Mass and Weight When you weigh something, what are you measuring? Weight is the measure of force acting on an object. Units of measure of weight are the same as that of force – Newton or kg m/s2. Since mass of an object remain constant; weight of the object is directly proportional to acceleration due to gravity.

  17. Where would you weigh moreEquator or Poles? Earth is not a perfect sphere. The radius of earth at the equator > radius of earth at the poles. Since acceleration due to gravity in inversely proportional to the distance. Earth’s gravity is therefore more at the poles and hence you will weigh more at the poles.

  18. Free fall When an object falls only under the influence of gravity then it is said to be in free fall. One experience weightlessness while falling freely. Equations of motion for objects in free fall – Since acceleration due to gravity always acts in the downward direction, g is always – 9.8 m/s2.

  19. Appendix

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