A limited math presentation of the concept of gravitational force for a high school astronomy class.

1. Newton’s Law of Universal
Gravitation
G = 6.67E-11 N. m2/kg2
Fg = GMm/r2

2. All Objects in the Universe pull on all
other objects.
• The distance (r) must be center to center.
•

4. Center to Center, even on earth.

5. From the earth, and between the
objects themselves.
Pull from man to earth.
Pull from center of earth to man.

6. How does the Solar System Work?

7. Here is the proof:

8. 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=MTY1Kje0yL
g
• 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.

9. From Kepler to Newton:

10. 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

11. 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.

12. 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