Q. Ball bearings are used in bicycles, cars, etc., because (UPSC Prelims 2013)
Answer:
the effective area of contact between the wheel and axle is reduced
Notes: The correct answer is
[C] the effective area of contact between the wheel and axle is reduced. This is a classic application of physics designed to minimize energy loss due to friction.The Physics of Ball BearingsTo understand why ball bearings are used, we have to look at the two main types of friction involved in a rotating wheel:
- Sliding Friction: This occurs when two surfaces rub directly against each other (like a flat block being pushed across a floor). It involves a large area of contact and high resistance.
- Rolling Friction: This occurs when a spherical or cylindrical object rolls over a surface.
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Why Ball Bearings Work:
- Conversion of Friction: Ball bearings convert sliding friction into rolling friction. Rolling friction is significantly weaker than sliding friction.
- Reduced Contact Area: By using small, hard steel balls between the moving axle and the stationary wheel hub, the "effective area of contact" is reduced to microscopic points on each ball.
- Minimal Resistance: Because the area of contact is so small, there is much less molecular "interlocking" between the surfaces, allowing the wheel to spin more freely with less heat generation and wear.