8. one point, from Lecture 8, involves words and minor calculation,

(a) .4 The force law for gravity. How is an object's weight related to the force of gravity on the object? (.1)
Why does the force of gravity depend on both masses? (.1)
Why does the force of gravity depend on the inverse square of the distance between masses, instead of the distance or inverse distance, for example? The answer is a plausibility argument. Use a sketch if you wish. (.1)
Why is the constant G needed in the force formula? (.1)

(b) .4 A strange and Universal Law. What is the meaning of "universal" in Newton's Universal Law of Gravity? (.1)
How can the weakest force in nature hold the whole universe together? (.1)
Why do we say the mass in Newton's 2nd Law is "inertial" mass and in Newton's Law of Gravitation is "gravitational" mass, when they are the same mass? (.1)

(c) .3 Understanding 1/r² forces. What happens to the force of gravity F between two objects when their separation distance r-->5r? (.1) r-->r/5? (.1)
Given the force F between two masses m1 and m2, what is the force (as a multiple or fraction of F) between 2m1 and 3m2? (.1)
Show that work, box those answers!

Revised September 22, 1997.