Ball bearing in the context of "Bearing (mechanical)"

Sphericity is a measure of how closely the shape of a physical object resembles that of a perfect sphere. For example, the sphericity of the balls inside a ball bearing determines the quality of the bearing, such as the load it can bear or the speed at which it can turn without failing. Sphericity is a specific example of a compactness measure of a shape.

Sphericity applies in three dimensions; its analogue in two dimensions, such as the cross sectional circles along a cylindrical object such as a shaft, is called roundness.

Bearing balls are special highly spherical and smooth balls, most commonly used in ball bearings, but also used as components in things like freewheel mechanisms. The balls themselves are commonly referred to as ball bearings. This is an example of a synecdoche. The balls come in many different grades. These grades are defined by bodies such as the American Bearing Manufacturers Association (ABMA), a body which sets standards for the precision of bearing balls. They are manufactured in machines designed specially for the job.

In 2008, the United States produced 5.778 billion bearing balls.

A jingle bell or sleigh bell is a type of bell which produces a distinctive 'jingle' sound, especially in large numbers. They find use in many areas as a percussion instrument, including the classic sleigh bell sound and morris dancing. They are typically used as a cheaper alternative to small 'classic' bells.

The simplest jingle bells are produced from a single piece of sheet metal bent into a roughly spherical shape to contain a small ball bearing or short piece of metal rod. This method of production results in the classic two- or four-leaved shape. Two halves may also be crimped together, resulting in a ridge around the middle. A glass marble may also be used as the ringer on larger bells.

Fluid bearings are bearings in which the load is supported by a thin layer of rapidly moving pressurized liquid or gas between the bearing surfaces. Since there is no contact between the moving parts, there is no sliding friction, allowing fluid bearings to have lower friction, wear and vibration than many other types of bearings. Thus, it is possible for some fluid bearings to have near-zero wear if operated correctly.

They can be broadly classified into two types: fluid dynamic bearings (also known as hydrodynamic bearings) and hydrostatic bearings. Hydrostatic bearings are externally pressurized fluid bearings, where the fluid is usually oil, water or air, and is pressurized by a pump. Hydrodynamic bearings rely on the high speed of the journal (the part of the shaft resting on the fluid) to pressurize the fluid in a wedge between the faces. Fluid bearings are frequently used in high load, high speed or high precision applications where ordinary ball bearings would have shortened life or caused high noise and vibration. They are also used increasingly to reduce cost. For example, hard disk drive motor fluid bearings are both quieter and cheaper than the ball bearings they replace. Applications are very versatile and may even be used in complex geometries such as leadscrews.