What is Newton's law of gravitation?

How is gravity related to the other fundamental forces?

What is the inverse square law? To what besides gravity does it apply?

Does the larger Earth exert a larger gravitational force on the smaller Moon than it exerts on the Earth?

What causes the tides? Why are there two per day instead of just one?

How does the force of gravity change with distance outside the Earth? inside the Earth?

If an object weighs 600 N at the Earth's surface, what will it weigh twice as far out from the Earth's center? ...three times as far out?

How would you calculate your weight in orbit?