Rolling Friction is a frictional force that opposes rolling objects. Rolling friction is applicable where the body moves along its curved surfaces. For example, wheels in vehicles, ball bearings, etc. are examples of rolling friction.

In this article, we will learn about rolling friction, its definition, laws, formulas, causes, coefficient, and the factors that affect it. We will also learn how rolling friction is different from sliding friction.

What is Rolling Friction?

Rolling friction is a type of friction, that opposes the motion of rolling objects. For example, if a ball is rolling on the floor, eventually it will stop. This happens because the ball is going to experience resistance in the direction of its motion. The frictional force acts on the ball, which is opposite to the motion of the ball and slows down the ball. The deformation of surfaces is the reason for rolling friction. Rolling friction is valid in the case for ball bearings-car tires, bowling balls, etc.

Rolling Friction Examples

Here are some examples of rolling friction

• Wheels of Vehicles: When vehicles move forward, they experience resistance to their motion due to contact with roads.
• Ball Bearings: Ball Bearings uses small metal balls, which creates rolling friction between wheels and axles
• Luggage Wheels: Trolleys use wheels that experience rolling friction when dragged on the surface and help to move heavy luggage with ease.
• Conveyor Belts: Conveyor belts at airports and metro stations are used to scan luggage. In these, rolling friction acts between the belt and the roller.

Laws of Rolling Friction

There are three laws of rolling friction:

Law 1: As the rolling friction becomes smoother, the weight acting on the wheels tends to decrease.

Law 2: Friction expressed as the product of load and constant where constant is raised to a fractional power.

F = kLⁿ

where F is Rolling Friction, K is frictional constant, L is load, n is fractional power.

Law 3: Load is directly proportional to rolling friction force, and the degree of curve is inversely proportional to the rolling friction force.

F = ???? ×W/r

Here, F = force of rolling friction

• μ = coefficient of rolling friction
• W = load (weight/mass)
• r = radius of curvature.

Rolling Friction Formula

Consider the following figure:

There are two formulas of rolling friction which are derived from the laws of rolling friction. The first formula related to rolling friction is given as:

F = KLⁿ

Here,

• F = rolling friction
• K = friction constant
• L = load
• n = fractional power

The second formula of rolling friction is given as

F = ???? ×W/r

Here, F = force of rolling friction

• μ = coefficient of rolling friction
• W = load (weight/mass)
• r = radius of curvature.

Cause of Rolling Friction

Rolling friction arises from several factors related to the interaction between a rolling object and the surface over which it rolls. The main causes of rolling friction include:

Deformation of Surfaces: When a wheel or a cylindrical object rolls over a surface, both the object and the surface undergo deformation. The surface deforms slightly under the pressure of the rolling object causing rolling friction to the wheel.

Elastic Hysteresis: Elastic hysteresis is the loss of energy that occurs when an elastic material, such as rubber, undergoes deformation and then returns to its original shape. As the tire or wheel rolls over the surface, it undergoes repeated cycles of compression and expansion, causing energy to be dissipated as heat. This also causes rolling friction.

Internal Friction: Internal friction within the material of the rolling object, such as the rubber in tires, also contributes to rolling resistance. As the tire rolls, internal friction within the tire material generates heat and dissipates energy, increasing the resistance.

Surface Irregularities: Surface irregularities, such as roughness, bumps, and imperfections, on both the rolling object and the surface over which it rolls can increase rolling friction.

Adhesion and Cohesion: Adhesion and cohesion between the rolling object and the surface can also contribute to rolling friction. Molecular interactions between the materials of the rolling object and the surface can create adhesion and cohesion forces, which resist the motion of the rolling object and increase rolling resistance.

Coefficient of Rolling Friction

The coefficient of rolling friction is the ratio of the rolling friction to whole weight of object. The coefficient of rolling friction when given may be formulated mathematically as

F= μ × W

• F= the magnitude of rolling resistance that corresponds to this given force.
• μ = coefficient of road resistance rolling
• W= load(weight)

Factors Affecting Rolling Friction

The following factors affect rolling friction:

• Nature of the surfaces: The more polished the surfaces are, the less turbulent the rolling resistance and vice versa.
• Material of the rolling body: The harder and the more inelastic the material of the rolling thing is, the smaller the rolling friction is. This is simply due to the fact that the body will be less deformed while rolling.
• Load on the rolling body: If pressure increases and load becomes higher the rolling body will deform more and this affects rolling friction.
• Radius of the rolling body: The larger the volume of the body in the rolling motion remains the smaller the rolling resistance. Thus, the body which have bigger radius will not be able to easily deform.
• Speed of the rolling body: With the higher speed of the body that is rolling, an enormous rolling friction comes. This to say that at high speeds slippage between the rolling body and the ground at high speeds will increase due to the rolling friction.

Difference Between Rolling And Sliding Friction

The differences between rolling friction and sliding friction have been listed in the table below: