Difference Between Sliding and Rolling Friction

Main Difference – Sliding vs. Rolling Friction

Sliding friction and rolling friction are both types of resistive forces that oppose an object’s motion along a surface. The main difference between sliding and rolling friction is that the sliding friction occurs when one surface is rubbing against another surface, whereas rolling friction occurs when an object is rolling on another surface.

What is Sliding Friction

Sliding friction (kinetic friction) is the force of friction between two surfaces which are rubbing against each other. Sliding friction is a consequence of having small protrusions on a surface. Whenever the two surfaces are moving against each other, the protrusions interlock and work needs to be done to keep the objects in motion.

Sliding friction f_k between two surfaces is given by:

f_k=\mu_kn

Where \mu_k stands for the coefficient of kinetic friction between the two surfaces, and n is the normal contact force between the surfaces.

What is Rolling Friction

Rolling friction occurs when the surface of one body is rolling against the surface of another body. The origin of this force is the deformations that occur on the surfaces as rolling occurs. Hysterisis is a main contributor: the energy given out when the surfaces recover their shape after a deformation is less than the energy that went in to create those deformations in the first place.

Analysing rolling friction is more complicated than analysing sliding friction. However, using a coefficient of rolling friction mu_r such that rolling friction f_r is given by 

f_r=\mu_rn

where n once again stands for the normal contact force. Writing down rolling friction in this form is helpful in comparing it with sliding friction. It is found that the rolling friction is much smaller compared to sliding friction. For instance, the coefficient of sliding friction between dry asphalt and rubber is 0.68 [1] while the coefficient of rolling resistance for a tyre on a road is in the range 0.01-0.035 [2]. However, this form of the equation is rather deceptive. In actuality, the “coefficient” depends on a number of other factors. For instance, for a tyre rolling on a road the coefficient changes with the radius of the tyre and how “full” the tyre is.

Difference Between Sliding and Rolling Friction

Difference Between Sliding and Rolling Friction – Rolling friction becomes important when riding a bike through sand

Difference Between Sliding and Rolling Friction

When it Occurs

Sliding friction occurs when two surfaces are rubbing against each other.

Rolling friction occurs when an object rolls on a surface.

Origin

Sliding friction occurs due to interlocking between microscopic “bumps” on surfaces.

Rolling friction occurs due to deformation of surfaces.

Dependance of Coefficient on External Factors

The coefficient of Sliding friction does not strongly depend on external factors. It is affected by the texture of surfaces and temperature by a small amount [3].

The coefficient of Rolling friction depends strongly on the radius of the rolling object, the depth to which the object sinks and the toughness of the surface and several other factors.

References
  1. Physics Study Guide/Frictional coefficients. (2009, July 17). Retrieved August 10, 2015, from Wikibooks: />
  2. TRIBOLOGY-ABC. (n.d.). Retrieved August 10, 2015, from Coefficient of friction, Rolling resistance and Aerodynamics: />
  3. Walters Forensic Engineering. (n.d.). SKIDMARK ANALYSIS & BRAKING. Retrieved August 10, 2015, from Walters Forensic Engineering Inc.: />
Image Courtesy
“Dumont Dunes, California. Rider, Kevin P. Rice, is on 2004 KTM EX/C 525 dirt-bike outfitted with paddle tire…” by Doug Fackiner (Self-made. SLORider.com) [], via

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