Rolling Friction: Definition, Examples, Laws, Causes, Coefficient and Formula

What is Rolling Friction Overview

Rolling friction, also known as rolling resistance, is a type of frictional force that occurs when one object rolls over another. It is an essential concept in physics and engineering, playing a crucial role in various fields such as transportation, mechanics, and everyday life. Understanding rolling friction is key to optimizing the design and performance of vehicles, machines, and even sports equipment. This article will provide a detailed explanation of rolling friction, including its definition, causes, and examples.

What is Rolling Friction?

The force that opposes the motion of a rolling body is referred to as rolling friction. When a ball is rolling on the ground, it ultimately comes to a stop. This is due to the ball encountering resistance in the direction of its velocity, meaning that a force is opposing the ball's motion and reducing its speed. Rolling friction is the name for this opposing force. The deformation of surfaces is the primary contributor to rolling friction. For instance, bowling balls, car tires, and ball bearings all experience rolling friction.

Advantages and Disadvantages of Rolling Friction

Formula for Calculating Rolling Friction

There are two formulas for rolling friction that are derived from the laws of rolling friction. These include:

F = KLn

Here, 

F= rolling friction

K = load

L = constant to fractional power.

F= μ×W/r

Here, 

F= force of rolling friction

μ = coefficient of rolling friction

W= load (weight/mass)

r = radius of curvature.

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Laws of Rolling Friction

As we previously discussed, rolling friction is based on three principles of motion, which are as follows:

• The amount of rolling friction decreases as smoothness increases.
• Rolling friction is a fractional power product of load and constant.
• The force of rolling friction is inversely proportional to the radius of curvature and directly proportional to the load.
• Rolling friction can be expressed as a fractional power of the product of the load and the constant: F = kLn 
• Rolling friction force is inversely proportional to curvature radius and directly proportional to load: F = μ×W/r

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What is Rolling Friction Cause

When an item rolls on the surface, certain things happen. As follows:

1. The item gets distorted when it comes into contact with the surface.
2. The item's surface deforms when it comes into contact with it.
3. The motion is created under the surface because of the concepts explained above.
4. The deformation energy is greater than the recovery energy, which is the primary cause of this friction. Additionally, there is a constant adhesive force acting between the two surfaces. 

The amount of friction is influenced by these factors, including:

• The quality of the sliding body 
• The surface's quality Load
• The diameter of the rolling object
• Area of the body's surface

What is Rolling Friction 

Although determining the coefficient of rolling friction is more difficult than determining the coefficient of sliding friction, the following statement and formula can help.

"The rolling friction coefficient is defined as the ratio of the rolling friction force to the total weight of the object."

Formula:

Fr =μrW 

Where, 

Frstands for the rolling resistance's resistive force.

μrstands for the rolling resistance coefficient.

Wis the weight of the moving body.

Solved Examples of Rolling Friction Coefficient

Example: A cart with a mass of 50 kg is rolling on a flat surface. The force required to keep the cart rolling at a constant speed is measured at 25 N. Calculate the coefficient of rolling friction.

Solution:

To calculate the coefficient of rolling friction, we can use the formula:

F = μ × W

where F is the force of rolling friction, μ is the coefficient of rolling friction, and W is the weight or load.

In this example, the force of rolling friction (F) is given as 25 N, and the weight (W) can be calculated by multiplying the mass (m) by the acceleration due to gravity (g), which is approximately 9.8 m/s^2.

W = m × g

W = 50 kg × 9.8 m/s^2

W = 490 N

Substituting the known values into the formula:

25 N = μ × 490 N

To isolate μ, we can divide both sides of the equation by 490 N:

25 N / 490 N = μ

0.051 = μ

Therefore, the coefficient of rolling friction (μ) in this example is approximately 0.051.

Rolling Friction Examples

Here are some examples of rolling friction in short and crisp points:

1. Vehicle Tires on Roads: Rolling friction between vehicle tires and the road surface provides traction for acceleration, deceleration, and turning.
2. Ball Sports: Rolling friction is essential in sports like soccer, basketball, and bowling, where the ball rolls on the playing surface.
3. Bearings: Rolling friction is utilized in bearings, such as those in wheels, rollers, and conveyor systems, to enable smooth rotation with reduced friction.
4. Skateboarding and Rollerblading: Rolling friction allows skateboard and rollerblade wheels to roll smoothly on the ground, enabling movement.
5. Bicycle and Motorcycle Tires: Rolling friction between tires and the road allows bicycles and motorcycles to move forward efficiently.
6. Luggage Wheels: Rolling friction enables luggage wheels to roll smoothly, making it easier to transport heavy bags.
7. Automotive Industry: Rolling friction affects fuel efficiency and tire wear in vehicles, prompting the development of low rolling resistance tires.
8. Industrial Equipment: Rolling friction is present in machinery and equipment with rotating parts, such as gears, pulleys, and conveyors.
9. Caster Wheels: Rolling friction in caster wheels allows easy movement of furniture, carts, and other objects.
10. Exercise Equipment: Rolling friction is involved in the movement of treadmills, elliptical trainers, and stationary bicycles.

Difference Between Rolling and Sliding Friction

The difference between sliding and rolling friction is that sliding friction happens when two surfaces rub against one another, whereas rolling friction happens when an object rolls on a surface.

Rolling Friction:

1. Rolling friction occurs when an object rolls on a surface.
2. It is caused by the deformation of surfaces and the interlocking between the rolling object and the surface.
3. The coefficient of rolling friction (μr) depends on factors such as the radius of the rolling object, the depth of deformation, and the surface characteristics.
4. The formula for calculating rolling friction is: Fr= μrN, where Fr is the rolling friction force, μr is the coefficient of rolling friction, and N is the normal force exerted on the object.

Sliding Friction:

1. Sliding friction occurs when two surfaces slide or rub against each other.
2. It is caused by the interlocking and interactions between the microscopic roughness of the surfaces.
3. The coefficient of sliding friction (μs) varies depending on factors such as surface roughness and temperature. It is generally considered an external property and is independent of the applied load.
4. The formula for calculating sliding friction is: Fk= μrN, where Fk is the sliding friction force, μs is the coefficient of sliding friction, and N is the normal force exerted between the surfaces.

What is Rolling Friction: Things to Remember

1. To slow down and eventually stop an object from rolling across a surface, rolling friction is the resistive force that any surface offers to oppose the object's rolling motion.
2. Increased smoothness results in a decrease in rolling friction force.
3. The load and curvature radius have opposite relationships for rolling friction force, which is directly proportional to load.
4. At the point of contact, the object and surface are both altered.
5. Since the friction on the former surface will be greater, a ball rolling on a field will travel less than a ball on a concrete floor.