Rolling Friction - Definition, Examples, Coefficient, Causes, FAQs

Rolling Friction - Definition, Examples, Coefficient, Causes, FAQs

Vishal kumarUpdated on 02 Jul 2025, 04:35 PM IST

We all know that it is very difficult to pull a heavy almirah on a rough floor. But, if we attach four iron wheels to the bottom of that almirah, then it becomes much easier to push or even pull it. The iron wheel or any of those wheels do not slide on the floor. However, the wheels roll on the floor.

Rolling Friction - Definition, Examples, Coefficient, Causes, FAQs
Rolling Friction

This proves that the surface of the wheel which is in touch with the ground does not rub against the ground and hence doesn't slide on it.

The velocity of the given point of contact of the wheel in relation to the floor remains zero, and hence, the wheel keeps moving forward.

What is Rolling Friction?

"The forces that resists the motion of a rolling body on a surface is called rolling friction."

The rolling of a football, tennis ball, or even a wheel on the ground is an example of Rolling friction.

What is Sliding Friction?

In this type of friction, there are restrictions on the body’s movement as only one side of the body gets in contact with the surface.

Pushing a box is an example of sliding friction. Rolling friction is a little weaker than sliding friction.

It is usually not always necessary for a wheel or even a sphere will roll. It may also slide depending upon its motion, and also the forces acting on it. Sometimes, just to reduce energy losses due to friction, small steel balls are included in the rotating parts of the wheel machines that are known as the ball bearings.

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Commonly Asked Questions

Q: What is rolling friction?
A:
Rolling friction is the force that resists the motion of a rolling object, such as a wheel or ball, as it moves along a surface. It's generally much less than sliding friction, which is why wheels are used to make movement easier.
Q: What's the difference between static and kinetic rolling friction?
A:
Static rolling friction is the force needed to start an object rolling from rest, while kinetic rolling friction is the force that continues to oppose the motion once the object is rolling. Static rolling friction is typically slightly higher than kinetic rolling friction.
Q: What's the relationship between rolling friction and energy loss?
A:
Rolling friction leads to energy loss as it converts kinetic energy into heat through deformation and other processes. This is why a rolling object will eventually come to a stop on a level surface if no additional force is applied.
Q: What's the relationship between rolling friction and the concept of rolling without slipping?
A:
For an object to roll without slipping, there must be enough friction to prevent sliding. This friction, while necessary for pure rolling, also contributes to rolling friction. The ideal amount allows for rolling without excessive energy loss.
Q: What role does rolling friction play in the concept of mechanical advantage?
A:
Rolling friction is an important consideration in mechanical advantage. While using wheels or rollers can greatly reduce friction compared to sliding, the remaining rolling friction still needs to be overcome. This affects the efficiency and required input force in mechanical systems.

Laws of Rolling Friction

There are basically three laws of rolling friction:

  1. The force of rolling friction decreases with an increase in smoothness.
  2. Rolling friction is often expressed as a product of load and constant to the given fractional power. $\mathrm{F}=\mathrm{KLn}$
  3. Rolling friction force is inversely proportional to the radius of curvature and is directly proportional to load. $F=\mu \times W / r$

Causes of Rolling Friction

When given objects or substances are rolled onto a surface, certain things happen:

  • The object is usually deformed at the point of contact with the present surface.
  • The surface is usually deformed at the point of contact with the present object.
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The motion is often created below the surface as a result of the above-mentioned two points.

The primary cause of this rolling friction is that the energy of deformation is usually greater than that of recovery energy. Also, an adhesive force exists between the two surfaces that need to be constantly overcome.

Coefficient of Rolling Friction

Determination of the coefficient of this friction is usually more complex than that of sliding friction.

“Coefficient of Rolling Friction is the given ratio of the force of rolling friction to the total weight of that object.”

The coefficient of rolling resistance in empirical terms can be expressed as:

$$
\mathrm{Fr}=\mu \mathrm{r} \mathrm{~W}
$$

where,

  • $\mathrm{Fr} \rightarrow$ resistive force of rolling resistance
  • $\mu \mathrm{r} \rightarrow$ coefficient of rolling resistance
  • $\mathrm{W} \rightarrow$ weight of the rolling body

Factors Affecting Rolling Friction

Following are some of the factors affecting rolling friction:

  • The shape of the given wheel or the given curved surface
  • Nature of the given surface on which the object is rolling
  • Wheel speed
  • Wheel radius
  • The nature of the wheel material or even the curved surface

Examples of Rolling Friction

  • A basketball that is rolled on the court will come to a halt due to its rolling friction.
  • A bike that has broad tires will eventually burn more fuel as compared to others because of the increased rolling friction.
  • A ball that is rolled on a field will go at a very lesser distance than that of a ball rolling on a concrete floor because it will eventually experience greater rolling friction on the former surface.

Difference between Rolling Friction and Sliding Friction

AspectsRolling FrictionSliding Friction
DefinitionResistance is when an object rolls over a surface.Resistance is when an object slides over a surface.
Motion TypeRolling motion (e.g., wheels, balls).Sliding motion (e.g., dragging a box).
Friction ForceLower than sliding friction.Higher than rolling friction.
Surface InteractionLess surface area in contact.More surface area in contact.
ExampleA car tire rolling on the road.Pushing a heavy box across the floor.
Ease of MovementEasier to move due to less resistance.Harder to move due to more resistance.

Frequently Asked Questions (FAQs)

Q: How might rolling friction be different in microgravity environments, such as on the International Space Station?
A:
In microgravity, the normal force between rolling objects and surfaces is greatly reduced, which in turn reduces rolling friction. However, other factors like adhesion between surfaces might become more significant. Understanding these differences is important for designing mechanisms that need to roll or rotate in space environments.
Q: How does the concept of rolling friction apply to non-circular objects, like a polygon "rolling" down an incline?
A:
For non-circular objects like polygons, the motion is not smooth rolling but a series of rotations and impacts. Each impact causes energy loss similar to rolling friction. The "effective" rolling friction for such objects is generally much higher than for circular objects, explaining why they come to rest more quickly on an incline.
Q: How does rolling friction relate to the concept of mechanical impedance?
A:
Rolling friction contributes to the mechanical impedance of a rolling system. It represents a form of energy dissipation that opposes motion, affecting how the system responds to applied forces or torques. Understanding this relationship is important in designing and analyzing dynamic mechanical systems.
Q: How does rolling friction affect the design of ball bearings?
A:
Ball bearings are designed to minimize rolling friction. They use hard, smooth materials and precise manufacturing to reduce deformation and surface irregularities. The size and number of balls are optimized to distribute load and minimize overall friction.
Q: Can rolling friction ever increase with use?
A:
Yes, rolling friction can increase with use due to wear and tear. As surfaces become rougher or materials deform permanently, rolling friction may increase. This is why regular maintenance and replacement of rolling components (like bearings or wheels) is important in many machines.
Q: Why do some vehicles use different tire widths on front and rear axles?
A:
Different tire widths can be used to balance performance characteristics. Wider tires may provide better traction but have more rolling friction. By using different widths, designers can optimize factors like steering response, traction, and overall rolling resistance for the vehicle's intended use.
Q: How does rolling friction affect energy conservation in physics problems?
A:
In many introductory physics problems, rolling friction is often neglected to simplify calculations. However, in real-world scenarios, rolling friction causes energy to be dissipated as heat, meaning that mechanical energy is not conserved. Accounting for this can be important in more advanced or applied problems.
Q: What's the relationship between rolling friction and the coefficient of restitution?
A:
While not directly related, both rolling friction and the coefficient of restitution affect the behavior of rolling objects. Rolling friction determines how quickly a rolling object will slow down, while the coefficient of restitution determines how much energy is conserved when the object bounces or collides.
Q: How does rolling friction affect the design of wind turbines?
A:
In wind turbines, minimizing rolling friction in the bearings is crucial for efficiency. Lower friction means more of the wind's energy can be converted to electrical energy. However, the bearings must also be designed to handle the large forces involved, which can increase friction.
Q: Why is understanding rolling friction important in robotics?
A:
Understanding rolling friction is crucial in robotics for accurate motion control and energy efficiency. It affects the power required for movement, the precision of positioning, and the overall performance of wheeled or rolling robotic systems.