gravity

Everyday gravity, the kind a person feels. On Earth it accelerates falling objects at roughly 9.8 meters per second squared. On other bodies the effect scales with their mass and radius. David Simpson, writing in The Guardian Weekly in 2013, could speak of escaping "the gravity of this world" and let the phrase lean toward its solemn sense as well.

Strictly speaking, physicists call this universal attraction gravitation. Using gravity for it is a loose extension of the earthly pull that gives weight, though the looseness is everywhere. The force between two masses grows with their product and weakens with the square of the distance between them. It is the weakest of the four fundamental interactions, yet it dominates on astronomical scales. In careful technical prose, gravitation is the safer word.

Mostly heard in a fixed frame: the gravity of the situation, of the issue, of a market's woes. Harry S. Truman opened his 1947 address to Congress with exactly that phrase. The noun usually follows the and takes an of-phrase naming what is serious. Seriousness and graveness can stand in for it, but gravity keeps the sense of weight it inherited from the Latin for "heavy".

Here gravity is an account of the force rather than the force itself. It usually takes a modifier naming the theory: Aristotelian, Newtonian, quantum. Because it names a theory, it can be counted, and rival gravities can be compared. Michael Riordan, writing in American Scientist in 2012, sets quantum gravity beside quantum electrodynamics as theories long dogged by infinities.

The literal sense, closest to the Latin: gravitās, "weight", from gravis, "heavy", borrowed into English in the 16th century. The same Latin word also gave English its doublet gravitas. Here the weight belongs to the object itself, such as an anchor, a bell or a cargo. That sets it apart from the pull that gives things weight, which is something the earth or moon does to an object rather than something the object has.

A clipped form of specific gravity, used when the context makes the full term unnecessary, as in testing battery acid or identifying a mineral. The figure is dimensionless. Water at 4 °C is the usual reference for liquids and solids, and air is the reference for gases. A value above one means the sample sinks in its reference, and a value below one means it floats.

A musician's word for depth of pitch, traditionally set against acuteness, the height of a note. In acoustic terms, a note of greater gravity has a lower fundamental frequency. The word describes a quality the listener hears, the darkness a bassoon or an organ's deepest pipes lend to a passage. It carries the same metaphor of heaviness as the word's Latin root.