Identify the incorrect statement.

Friction is the force that opposes relative motion (or the tendency of motion) between two surfaces in contact. Its magnitude depends on the nature of the surfaces and the force pressing them together; it can be reduced by lubrication, polishing, or by replacing sliding contact with rolling contact, but it can never be brought to exactly zero on Earth.

Rolling friction (the friction of a rolling surface, as in a ball or roller bearing) is always much smaller than sliding friction between the same pair of surfaces, because rolling involves far less deformation and surface interlocking than sliding. This is precisely why ball bearings are built into machines: they let one part rotate against another via rolling contact instead of sliding contact, which lowers friction, wear, and heat generation — not raise it.

Applying this to each statement:

• “Ball bearings are used to increase friction between parts of a machine” reverses their actual engineering purpose: bearings convert sliding motion into rolling motion specifically to cut friction down, so this statement is false.

• “Friction between two surfaces in contact can never be eliminated on earth” is true — friction can be minimised but some residual resistance always remains between any two real surfaces.

• “Rolling friction is less than sliding friction” is true — this is exactly the physical principle bearings, wheels, and rollers rely on.

• “The friction force on an object moving through a fluid depends upon its shape” is true — fluid (drag) friction is smaller for streamlined shapes and larger for blunt/irregular shapes moving at the same speed through the same fluid.

Cross-check: if ball bearings genuinely increased friction, they would increase wear and heat in every rotating machine part they are fitted to — the opposite of why engineers use them in wheels, axles, and motors for smooth, low-friction rotation. So the statement about ball bearings is the one statement that does not hold, making it the incorrect statement asked for.