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Ch 2 -newton’s law of universal gravitation

Date post: 25-May-2015
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A limited math presentation of the concept of gravitational force for a high school astronomy class.
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Newton’s Law of Universal Gravitation G = 6.67E-11 N . m 2 /kg 2 F g = GMm/r 2
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Page 1: Ch 2 -newton’s law of universal gravitation

Newton’s Law of Universal Gravitation

G = 6.67E-11 N . m2/kg2

Fg = GMm/r2

Page 2: Ch 2 -newton’s law of universal gravitation

All Objects in the Universe pull on all other objects.

• The distance (r) must be center to center.

Page 3: Ch 2 -newton’s law of universal gravitation
Page 4: Ch 2 -newton’s law of universal gravitation

Center to Center, even on earth.

Page 5: Ch 2 -newton’s law of universal gravitation

From the earth, and between the objects themselves.

Pull from center of earth to man.

Pull from man to earth.

Page 6: Ch 2 -newton’s law of universal gravitation

How does the Solar System Work?

Page 7: Ch 2 -newton’s law of universal gravitation

Here is the proof:

Gravity_Experiment.flv

Page 8: Ch 2 -newton’s law of universal gravitation

Science Fiction?

• "The Force is what gives a Jedi his power. It's an energy field created by all living things. It surrounds us and penetrates us. It binds the galaxy together.“

• https://www.youtube.com/watch?v=MTY1Kje0yLg

• Truth: Gravity is an energy field; It surrounds us and binds the OBJECTS in the UNIVERSE together. It is a force. Just not THE force. And it is with us.

Page 9: Ch 2 -newton’s law of universal gravitation

From Kepler to Newton:

Page 10: Ch 2 -newton’s law of universal gravitation

Example Problems: Finding g on any planet.

• g = Gm/r2

• What is the acceleration of gravity on Earth?• G = 6.67e-11• mearth = 5.98e24 kg• earth radius = 6400e3m• g = 6.67e-11 * 5.98e24/(6400e3)2 • g = 9.8 m/s2

Page 11: Ch 2 -newton’s law of universal gravitation

Way to find the mass of the earth.

• g = 9.8 m/s2 was already known, Newton could calculate G = 6.67e-11, and the radius of the earth was

already known. So with those values scientists were able to calculate the mass of the earth.

Page 12: Ch 2 -newton’s law of universal gravitation

Find the mass of Mars:

• g = 3.5 m/s2 on the surface. • radius of Mars = 3390 km or 3390e3 m G = 6.67e-11

3.5 = 6.67e-11 * m/(3390e3)2 Solve for m (3.5 * 3390e3)2/6.67e-11 = m


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