Five metallic balls on slender threads sit side by side. As one on the end hits the rest, the one on the opposite end rises and falls. Why don't the balls in the middle move? It's complicated. See more »

Air, the mixture of gases that surrounds the earth and forms the earth's atmosphere. See more »

Ballistics, the science that deals with the motion of projectiles such as bullets, shells, rockets, and aerial bombs. See more »

Falling Bodies, objects moving downward under the influence of gravity. The nature of this motion is the same for an object that falls straight down as it is for one that moves forward and down at the same time. See more »

Force, in physics, the pushing or pulling agency that makes (or tends to make) objects speed up, slow down, or change direction. See more »

Friction, the force or resistance that opposes the movement of one body or substance against another. See more »

Hydromechanics, the branch of physics that deals with forces acting upon and within fluids (liquids and gases). See more »

Lever, a rigid rod or bar to which a force may be applied to overcome a resistance. See more »

Pendulum, an object connected to a fixed support in such a way that it is free to swing back and forth under the influence of gravity. See more »

Siphon, a bent tube used to move a liquid over an obstruction to a lower level without pumping. See more »