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# GRAVITY

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## DC Physics

on 18 April 2016

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#### Transcript of GRAVITY

GRAVITATIONAL FIELDS
Uses
Looking at the Apollo 11 data show graphically that force (acc) is inversely proportional to the square of the distance.

Use the gradient of the graph to find a value for G
(the mass of the earth is 6*10^24kg)

Newton's Law of Gravitation
Gravitational Field Strength
Gravitational Potential
Ideas Before Newton
Kepler had noted that from his observation of stars that:

The path of the planets about the sun is elliptical in shape, with the center of the sun being located at one focus. (The Law of Ellipses)
An imaginary line drawn from the center of the sun to the center of the planet will sweep out equal areas in equal intervals of time. (The Law of Equal Areas)
The ratio of the squares of the periods of any two planets is equal to the ratio of the cubes of their average distances from the sun. (The Law of Harmonies)
Why are there 2 tides on the earth and not one?
Why is the Force of gravity on Jupiter larger than Earth if the radius from the center of the planet is larger?
If you dropped a ball through the centre of the earth, would it exhibit SHM?

Simple Harmonic Motion?
Why is the shuttle launched from Florida, the Soyuz rocket from Kazakhstan, and ESA rockets from French Guiana?
Can you prove that force is proportional to radius?
If so what would be the time period assuming an average denisty of 5500kg/m^3 and a radius of 6400km
Can you prove Kepler III -

Using Kepler III and the knowledge that light takes 8.5 mins to reach earth, find the mass of the sun
What is the average density of a super massive black hole or mass 10^39Kg?
What is the distance of a geo-synchronous satellite from earth?
What is the distance of the ISS if the period of rotation about the earth is 100mins?
http://what-if.xkcd.com/67/
http://what-if.xkcd.com/68/
ANS
ANS
What if?
Saturn 5 rocket launch
Understanding of the definition of gravitational potential, including zero value at infinity, and of gravitational potential difference.
If you wanted to move to a lower orbit, which way would you fire your rockets?
ANS