1. Universal Gravitation
Ch3
Universal Gravitation

2. Gravity
If the force of gravity is being exerted on objects on Earth, what is the origin of that force?
Newton’s realization is that it must have come from the Earth
He realized that gravity must be what keeps the Moon in orbit

6. Applying the Law of Universal Gravitation
There are 2 equal, but opposite forces present.
For the force of attraction to be noticeable, at least one of the objects must be very large
The inverse square relationship between FG and r means the force of attraction diminishes rapidly as the two objects move apart
Also, there is no value of r, that would make this force 0
This equation only applies to spherical objects, to two objects whose sizes are much smaller than their separation distance

11. Example 2 - Spacecraft

13. 3.4 Satellites & space stations

14. Satellite Motion
A satellite is an object or a body that revolves around another body.
Satellites can be categorized as natural satellites or man-made satellites.

15. Satellites in Circular Orbit
Newton related the cause for heavenly motion (the orbit of the moon about the earth) to the cause for Earthly motion (the falling of an apple to the Earth) and this led him to his notion of universal gravitation.
He surmised that the same force that pulled an apple downward as it fall from a tree was responsible for keeping the Moon in orbit

16. Satellites in Circular Orbit
Why doesn’t the moon hit the ground?
The Moon travels at the speed that keeps it at approximately the same distance, called the orbital radius, from Earth’s centre.
As the moon circles Earth, it is undergoes constant free fall toward Earth (same is true for all natural and artificial satellites).
A satellite pulled by the force of gravity toward Earth follows a curved path.
Since Earth’s surface is curved, the satellite falls downward at the same rate as Earth’s curvature
If the orbiting free-falling satellite, has the proper speed for its orbital radius as it falls toward Earth, it will never land.

17. Motion of a Satellite in Uniform Circular Motion
Combining Newton’s law of Universal Gravitation, and equation for Centripetal Acceleration involves the satellite’s speed.
Used to analyze the motion of a satellite in uniform circular motion

18. Apparent Weight
Apparent Weight: the net force exerted on an accelerating object in an non-inertial frame of reference

19. Classwork & Homework