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Rolling friction
Intermediate
Smaller resistance of rolling wheels compared with sliding.
A rolling wheel deforms the surface slightly, giving a resisting force much smaller than sliding friction (Frr = μᵣN with μᵣ ≈ 0.01). This is why wheels are so useful.
A car tyre on road: μᵣ ≈ 0.015.
Pure rolling without slipping involves static friction at the contact point that does no work.
In more detail
Rolling friction resists a rolling wheel or ball, due to deformation of the surfaces. It is usually much smaller than sliding friction, which is why wheels are efficient.
Real-world uses
- Car tyres are designed to minimise rolling resistance for better fuel economy.
- Ball bearings reduce friction by replacing sliding with rolling.
- Ball bearings and wheeled suitcases reduce resistance by rolling rather than sliding.
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Frequently asked questions
Why is rolling friction smaller than sliding friction?
Rolling involves less continuous deformation and no continuous sliding of surfaces against each other.
Does rolling friction depend on speed?
In the simple model, no, but in practice it can increase at higher speeds.
Does rolling friction disappear completely?
No. It is small but not zero, because the surfaces deform slightly as the wheel rolls over them.
Related topics in Newton's Laws & Forces
Static friction · Kinetic friction · Angle of friction and repose · Friction on inclines with applied force · Block on block problems · Impulse