# Ch. 12-14 - Gravity

## New Terms in Ch 12-14: inverse-square law Law of Universal Gravitation ellipse perturbation universal gravitation constant, G action at a distance field tide tidal bulge black hole singularity escape energy escape speed Ch 12-14 Objectives:

When you complete chapters 12-14 you should be able to:

Ch 12 - Universal Gravitation

1. ... briefly describe the ideas of Ptolemy, Copernicus, Brahe, Galileo, and Kepler, Newton, Cavendish, and von Jolly with regard to the motion of planets in the Solar System and the Law of Universal Gravitation.
2. ... recognize that the Law of Universal Gravitation applies to all objects that have mass.
3. ... tell what "inverse-square law" means and state that Newton's Law of Universal Gravitation is an inverse-square law.
4. ... discuss how mass and distance affect gravitational force.
5. ... calculate the gravitational force between two objects, given their masses and separation.
6. ... recognize that Newton's Law of Universal Gravitation explains the motion of planets in the Solar System.

Ch 13 - Gravitational Interactions

1. ... distinguish between the concepts "action at a distance" and "gravitational field."
2. ... calculate the gravitational field strength, g, at a given point in space given an object's mass and the gravitational force on this mass.
3. ... explain how "weightlessness" works.
4. ... recognize that tides on Earth are mainly caused by the gravitational force on Earth due to the Moon, and explain why the tides on Earth are affected more by the Moon than the Sun.
5. ... recognize how the Law of Universal Gravitation applies to black holes.

Ch 14 - Satellite Motion

1. ... use the terms frequency, period, apogee, and perigee in discussing orbital motion.
2. ... for an object in a circular orbit, discuss:
1. the force exerted on it.
2. its acceleration.
3. its speed and velocity.
4. its momentum.
5. its kinetic energy.
6. its gravitational potential energy.
7. work done on it by the gravitational force
3. ... for an object in an elliptical orbit, discuss:
1. the force exerted on it.
2. its acceleration.
3. its speed and velocity.
4. its momentum.
5. its kinetic energy.
6. its gravitational potential energy.
7. work done on it by the gravitational force.
4. ... discuss escape speed/velocity/energy for an object in a gravitational field.

## Possible Preconceptions to Correct:

Do you believe that any of the following statements are true? They AREN'T! When you finish Chapters 12-14, you should understand that each of these statements is FALSE, and WHY it is false .

• FALSE: Gravitational force has something to do with air.
• FALSE: There is no gravitational force outside Earth's atmosphere.
• FALSE: The weight of an object is a constant property of the object.
• FALSE: When an object becomes a black hole, its gravitational field suddenly increases dramatically.

last update June 8, 2008 by JL Stanbrough