Which describes one way that Aristarchus's explanation of the movement of objects in the sky was different from other scientists' earlier explanations?He discovered Venus’s phases. He argued that Earth rotates on its axis. He explained the concept of retrograde motion. He described the epicycles of the planets in the sky.

Consider a small frictionless puck perched at the top of a fixed sphere of radius r. if the puck is given a tiny nudge so that it begins to slide down, through what vertical height will it descend before it leaves the surface of the sphere? [hint: use conservation of energy to find the puck's speed as a func e conservation of energy to find the puck's speed as a function of its height at what value of this normal force does the puck leave the sphere? ] here on the puck.