Review

#04

Heliocentrism, but still required uniform circular motion.

#08

Mainly, Venus showed a full range of phases as expected by the heliocentric model, in contrast to primarily crescent phases expected by the geocentric model.

#14

Newton's laws of motion indicate that objects travel in straight lines at constant speed unless acted on by a force, that forces produce accelerations that are inversely proportional to an object's inertia, and that every action yields an equal but opposite reaction. The law of gravity is a particular force that acts on mass, is proportional to their mass and attractive, and is weaker when objects are farther apart.

#16

Although both the ball and the Earth experience the same force of gravitational attraction, the intertia of the Earth is much much more, and so its acceleration incredibly tiny. As such, the Earth hardly moves at all, and all of the motion is in the ball. Hence the ball falls toward the Earth.

#19

It is the speed required for something to move away from a body of mass and only just never quite fall back again.

#20

It would travel in a straight line at constant speed with a trajectory tangent to its orbit at the time when the force was ``turned off''.