Grades 3–5 · Machines
How can tiny steel balls help a wheel turn?
A wheel needs support at its center, but it also needs to turn. In a ball bearing, two strong rings have smooth grooves called raceways. Small balls sit between the rings, touching both of them.
In the diagramRolling contacts support a turning shaftFace-on construction view · ball locations held fixedInner ringBallsOuter ringSpacing cageShaftThe load crosses the balls; rolling still has some friction.
One ring can turn with the shaft while the other stays with its housing. The balls roll along the grooves, allowing the rings to move relative to each other with much less resistance than many plain rubbing surfaces. The load passes through the contacts from one ring, through the balls, to the other ring.
A cage keeps neighboring balls apart. Lubricant reduces wear and friction at the contacts, and many bearings have seals or shields to help keep dirt out. Rolling does not remove all friction: the materials deform slightly, and some sliding and lubricant resistance remain.
About this explanation
Starting knowledge: Recognize a shaft, rolling and rubbing.
Sources
- SKF — Rolling bearings: Bearing basics and terminology