A manifold is a topological space that is locally Euclidean (i.e., around every point, there is a neighborhood that is topologically the same as the open unit ball in R^n). To illustrate this idea, consider the ancient belief that the Earth was flat as contrasted with the modern evidence that it is round. The discrepancy arises essentially from the fact that on the small scales that we see, the Earth does indeed look flat. In general, any object that is nearly "flat" on small...

An Asian version of chess, sometimes also called Chinese Chess, that is currently played extensively in China, Taiwan, Thailand, Singapore, Vietnam, and Hong Kong. The Xiangqi board consists of ten horizontal lines and nine vertical lines. The verticals are interrupted by a central horizontal row called a river, and two palaces are positioned at opposite sides of the board (Bodlaender).

See also: Engine, Simple Machine, Wimshurst Machine

The Coriolis force is a fictitious force exerted on a body when it moves in a rotating reference frame. It is called a fictitious force because it is a by-product of measuring coordinates with respect to a rotating coordinate system as opposed to an actual "push or pull." See also: Coriolis Acceleration, Coriolis Frequency, Coriolis Parameter, Rossby Number

Quantum entanglement describes the very strong correlation that can exist in quantum systems This Demonstration shows two simple experimental setups in which pairs of polarized photons are generated by a source and the photons in each pair are subsequently detected in different polarization bases The photons on the left are in the singlet state which is entangled The photons on the right are in th