Discussion
Identify the incorrect statement.
Answer: A
The incorrect statement is that ball bearings are used to increase friction between parts of a machine.
Ball bearings replace sliding with rolling, and rolling friction is much smaller than sliding friction, so they are used to reduce friction, for example in the hubs of bicycles and the shafts of fans and motors.
The other statements are correct: friction can be reduced but never completely eliminated on Earth, since no surface is perfectly smooth; rolling friction is less than sliding friction; and the drag on an object moving through a fluid depends on its shape, which is why aeroplanes and fish are streamlined.
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