Rolling friction

Introduction

Rolling friction is the type of friction in which the force resists the rolling object's motion on the surface. Rolling friction assists in minimising the friction between the surface and an object which is relatively lower as compared to sliding friction. Rolling friction permits the object to go smoothly over the surface and roll up the hill. The wheels fitted on the luggage work on the concept of rolling friction as it is rolled and moved easily with the wheel. At a certain point, the surface and object deform in rolling friction due to certain factors such as roughness, weight and elasticity. The direction of rolling friction is similar to that of transitional friction.

What is Rolling Friction?

Rolling friction is demonstrated as the force of friction that happens when any sort of object roll on the other. Objects that are "spinning without slipping" face the rolling friction, not the kinetic friction. This type of friction as repelled to the sliding friction where a specific side of an object is in touch with the surface throughout the motion duration. It is demonstrated that rolling friction is often less in magnitude in comparison to that of sliding friction (Xie, Ma & Zhao, 2019). Rolling friction is influenced by different factors. The formula of rolling friction is $\mathrm{F \:=\:C_{rr}N}$, where F is the force, $\mathrm{C_{rr}}$ is the dimensionless coefficient of rolling resistance and N is the normal force.

Figure 1: Rolling friction

The most prevalent factors that impact the rolling friction's magnitude are surface deformation and internal compressions that is the movement below the surface. The other factors such as the diameter of the wheel, sliding and surface adhesion, and relative sliding between the contact surfaces also influence the rolling friction (Maeda & Iwasaki, 2018). Sand often offers higher rolling friction in comparison to solid surfaces such as concrete due to micro sliding factors.

Laws of rolling friction

The sliding friction laws cannot be appropriate to the rolling bodies in the similar quantitative terms but the following generalities of laws of rolling friction:

• The force (F) of rolling friction is proportionate to the load (L) and is inversely comparable to curvature radius (r). F = r L/r, where r denotes rolling resistance’s coefficient in inches (Shcherbakov et al. 2021). The frictional forces minimise as the radius maximises.

• The force of rolling friction (F) is expressed as the power of friction of the load (L) multiplied as constant k. $\mathrm{F = kL^n}$, where the power (n) and constant (k) are determined experimentally.

• The force of rolling friction minimises as the rolling component’s smoothness develops.

What is the coefficient of Rolling Friction?

The coefficient of rolling friction is mentioned as the force ratio of "rolling friction" to the ultimate weight of the object. Empirically, it can be represented as $\mathrm{F_r = \mu_r\: W}$. F_r in this formula denotes the resistive force of rolling resistance, μr is the rolling resistance’s coefficient and W denotes the weight. The coefficient of rolling friction is calculated in a formulative manner as μ_r = F/G. F is referred to as the force needed to pull the tire axle horizontally in the travel direction (Ndiaye et al. 2021). G denotes the tire's vertical load the tire which is predicted to roll on the flat surface horizontally.

What is the reason for occurring of rolling friction?

The basic reason for the friction is the deformed energy which is larger as compared to the recovery energy. There is a sticky force between both the surfaces which is required to be overcome continuously (Hayashi et al. 2020). The friction amount is based on certain factors such as load, surface quality, rolling object’s diameter, body surface area and sliding body quality.

Figure 2: Rolling friction

The cause of rolling friction is almost similar to that of friction that is the deformation only. Certain things occur when a thing or an object is rolled on a particular surface (Tiwari, Miyashita & Persson, 2019). The motion is made below the surface consequences of surface and object deformation. Deformation of the object is seen at the contact point with the surface. Deformation of the surface is seen at the contact point with the object.

What is the difference between sliding and rolling friction?

Rolling friction	Sliding friction
It happens when the object rolls on any surface area.	It takes place when both the surfaces are stroked against the other.
Surface deformation is the main cause of rolling friction.	Interlocking between microscopic surfaces is the main reason for sliding friction
Rolling friction’s coefficient is $\mathrm{F_r\: =\: \mu_r N}$	Sliding friction’s coefficient is $\mathrm{F_k\: =\: \mu_r N}$

Table 1: the difference between rolling and sliding friction

Examples

Figure 3: Rolling friction of the car

The rolling of basketball on the court may eventually emerge to a halt due to rolling friction. Cars with broad tires may burn more fuel because of the maximised rolling friction (Ciornei et al. 2019). The rolling of a ball on a field may go fewer distances as compared to a ball rolling on a rough floor because it may face greater friction of rolling on the present surface.

Conclusion

The special kind of rolling friction is termed traction. Rolling is generally a form of rotation and transition motion. The loss of hysteresis predominantly relies on the material nature of the surfaces involved influences the happening of rolling friction. Rolling friction is often demonstrated as the weakest type of friction. Its coefficient is based on the rolling object's radius, the depth to the sinking of the object and surface roughness. Sliding friction's coefficient relies on the surface texture and temperature to a certain extent which is not dependent on external factors.

FAQs

Q1. What are the impacts that disturb a vehicle's rolling resistance?

Ans. Factors that impact the distortion of the rolling friction are tire diameter, tire pressure, tire width, tire tread and tire construction. The factors are applicable when the pressure is maximised, and the tire deformation is less.

Q2. Does the rolling friction rise with velocity?

Ans. The rolling resistance's force does not change at the highest speed. The cyclists use more energy per second the labour alongside rolling friction.

Q3. What is meant by Kinetic friction?

Ans. Kinetic friction is demonstrated as the friction that performs between both stationary surfaces. The formula of kinetic friction is $\mathrm{F_f\: =\: \mu_k FN}$.

Q4. What is the unit of rolling friction’s coefficient?

Ans. The unit of rolling friction’s coefficient is Newton's (N). The equation of this friction is similar to sliding friction and static friction.