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 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. Distance d 1

Newton’s hypothesis Just pushed over the table with force F 1 Pushed with more force F 2 If you push the ball harder (i.e. apply more force) the ball travels a longer distance horizontally before reaching the ground. Distance d 1 Distance d 2

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.

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.

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

Does Gravitational Force depend on distance?

Factors influencing Gravitation Force

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 = MMass = m

Does the apple also pull the earth?

Acceleration due to Gravity

Gravity on the surface of earth

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

Gravity on surface of Jupiter

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/s 2.

Where would you weigh more Equator 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.

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.

APPENDIX