Conceptual Physics Notes on Chapter 12 Universal Gravitation

Conceptual Physics Notes on Chapter 12 Universal Gravitation

Universal Gravitation n Isaac Newton and the falling apple --- n Newton was under a apple tree when a apple hit him on the head and he got an idea that changed the world. n What was his GREAT idea? ….

Universal Gravitation n Isaac Newton and the falling moon --- n Newton compared a falling apple to the moon in orbit around the Earth. He said that the moon fell toward the earth as fast as it moved in a straight line - tangential velocity.

Universal Gravitation n Newton “generalized” his moon findings to ALL objects, and said that ALL objects in the universe attract each other. (Law of Universal Gravitation)

Universal Gravitation NEWTON’S LAW OF UNIVERSAL GRAVITATION n Every object attracts every other object with a force directly proportional to the mass of each object, but decreases as the square of the distance between masses. F ~ m 1 m 2 2 d

Universal Gravitation n We want the force to equal, so we have to add a constant to the equation. G = 6. 67 x -11 10 kg (Note that the force of gravity is very weak) n Henry Cavendish measured G 150 years after Newton’s Law listed above and was said to have WEIGHED the world!

Universal Gravitation

Universal Gravitation n So the equation becomes: F = G m 1 m 2 2 d

Universal Gravitation Inverse-square Law: The brightness of an object decreases dramatically as we move farther from the source. The result is due to a larger "sphere" of influence. Light from a source like a star shines in all directions, to the area of illumination increases with increasing distance so the total brightness thins out.

Universal Gravitation

Universal Gravitation EXAMPLES: n 32 =9 n 2 d 2 = 4 d but 1/32 = 1/9 but 1/2 d 2 = 1/4 d (Note that as the distance gets LARGER, the overall force gets smaller)