bearing

Three types of bearing. The roller and the ball bearing are similar, differing only in the shape of the parts that roll when the middle shaft turns. The simpler journal bearing consists of a sleeve, or journal, lining the surface of the rotating shaft. The bearing is lubricated to reduce friction and wear.

Device used in a machine to allow free movement between two parts, typically the rotation of a shaft in a housing. Ball bearings consist of two rings, one fixed to a housing, one to the rotating shaft. Between them is a set, or race, of steel balls. They are widely used to support shafts, as in the spindle in the hub of a bicycle wheel.

The sleeve, or journal bearing, is the simplest bearing. It is a hollow cylinder, split into two halves. It is used for the big-end and main bearings on a car crankshaft.

In some machinery the balls of ball bearings are replaced by cylindrical rollers or thinner needle bearings.

In precision equipment such as watches and aircraft instruments, bearings may be made from material such as ruby and are known as jewel bearings.

For some applications bearings made from nylon and other plastics are used. They need no lubrication because their surfaces are naturally waxy.

bearing

A bearing is the direction of a fixed point, or the path of a moving object, from a point of observation on the Earth's surface, expressed as an angle from the north. In the diagram, the bearing of a point A from an observer at B is the angle between the line BA and the north line through B, measured in a clockwise direction from the north line.

Direction of a fixed point, or the path of a moving object, from a point of observation. Bearings are angles measured in degrees (°) from the north line in a clockwise direction. A bearing must always have three figures. For instance, north is 000°, northeast is 045°, south is 180°, and southwest is 225°.

True north differs slightly from magnetic north (the direction in which a compass needle points), hence northeast may be denoted as 045M or 045T, depending on whether the reference line is magnetic (M) or true (T) north. True north also differs slightly from grid north since it is impossible to show a sphere on a flat map.

Finding a bearing To find the bearing of B from A, start at A facing north then turn clockwise until facing B. The bearing of B from A is the angle shaded:

To find the bearing of A from B, start at B facing north, then turn clockwise until facing A. The bearing of A from B is the angle shaded:

Problem solving Trigonometry, Pythagoras' theorem, and scale drawings are often used when solving problems involving bearings.

For example, if a ship sails from harbour to an island 10 km away on a bearing of 030°, then continues on from the island at a bearing of 180° to a point that is on a bearing of 090° from the harbour, it is possible to measure how far the ship is from the harbour using trigonometry.

sin 30° = opp/hyp = distance from harbour/10 10 × sin 30° = distance from harbour = 5 km