Introduction
Frictional forces that oppose an object's motion across a surface include sliding friction and rolling friction. The force of friction prevents adjacent objects from gliding past one another. Analyzing rolling friction is more challenging than sliding friction. The kinetic friction involved in sliding is typically higher than the rolling friction.
Let’s understand the differences between sliding friction and rolling friction in a bit more detail.
Sliding Friction vs Rolling Friction
Now, the primary distinction between sliding friction and rolling friction is that sliding friction takes place whenever two contacts come into touch with one another, on the other hand rolling friction takes place when an object rolls over a surface. Rolling friction is not a type of friction, but sliding friction can be.
A straightforward principle with numerous applications is sliding friction. A flat finish is not found in the actual world. An object receives a rearward force when it slides on any surface because of the relative velocity between the two neighboring surfaces. Motion has always been opposed by sliding friction. We encounter sliding friction whenever we attempt to slide an object across a flat surface, such as a cabinet.
It is believed that the invention of the circular wheel marked a turning point in human history. The requirement to roll an object gave rise to the first wheel. When an object rolls on a surface, rolling friction acts as a force to stop it from moving. Ideally, there should be no sliding friction between the surfaces that are in contact when something rolls smoothly on one. However, in actual use, the surface's elastic qualities cause both the body and the surface to bend.
Difference Between Sliding Friction and Rolling Friction in Tabular Form
| Parameters of Comparison | Sliding Friction | Rolling Friction |
| The Occurrence | The link between the size of tiny bumps on surfaces is what causes this to happen. | The cause of this is surface deformation. |
| The Type of Friction | The friction that slides may be tolerated. | Rolling friction is not a resistive force; it is a type of friction. It's crucial to keep in mind that not all resistance is friction. |
| The Dependence of the Coefficient | The minuscule amount of heat that is readily available and the design of the surfaces affect the coefficient, which is not just a result of external factors. | The coefficient depends on the radius of the rolling item, the depth at which it descends, and the composition of the surface layer, among other factors. |
| The Type of Resistance | Sliding friction acts as a constant external force throughout the contact region to stop relative motion. | To stop the rolling motion, rolling friction creates a torque in the opposite direction. |
What is Sliding Friction?
We can think of sliding friction as the force that opposes any two bodies sliding against one another. This friction, which is also known as kinetic friction, is the force needed to keep one surface moving along another. It depends on two factors: the object's weight and size and the substance the thing is made of. The sliding friction is unaffected by changes in the surface area in contact. The majority of materials have substantially lower sliding friction than static friction.
In contrast to rolling friction, which is the frictional force caused by the rotating movement of a roughly disc-like or another circular item along a surface, sliding can take place between two objects of any form. The frictional force associated with rolling friction is often substantially lower than that associated with sliding kinetic friction. The coefficient of rolling friction often has lower values than the coefficient of sliding friction. Similar to rolling friction, sliding friction typically generates higher thermal and acoustic byproducts.
When calculating the extent of roadway noise pollution, one example is the braking of motor vehicle tires on a road, which produces a significant amount of heat and sound. We can use the simple example of how our car slows down when we stop at a stop sign because of friction between the applied breaks and the wheels. As a result, sliding friction is the force that acts in the opposite direction of where a body wishes to slide. Rolling, sliding, static, and fluid friction are some important types of friction. Here, we'll talk about kinetic friction, often known as sliding friction, its measurement coefficient, and several examples.
Sliding or kinetic refers to the resistance to actual relative sliding between two surfaces in contact. Let's begin by exploring frictional forces using a straightforward concept. Let's say a metal block is on a table; a weak force might not move the metal block. The metal block begins to move as you progressively generate more power, up up to a specific amount. The resistive force generated by the metal block in its static form is the same as the regulating value of the pressure at which the metal block begins to move.
Now, static friction is the term given to a certain resistant force. The metal block starts to shift when the force is greater in the experiment. However, after the metal piece began to move, it also continues to exert a resistant force to prevent the movement. It is known as sliding friction. It is now obvious from what we have said so far that the slide resistance is less than the static friction.
When moving in a direction normal to the surface, the force of sliding friction is precisely proportional to the weight. In particular, if the body is sliding over a horizontal surface, the normal force will be equal to the object's weight.
Moving friction caused or generated by objects is referred to as a coefficient that takes into account several variables that may have an impact on the amount of friction. The following are some of the many variables that might affect sliding friction:
- An object's surface deformation.
- The surface's smoothness or roughness.
- The speed of either object at its launch.
- The object's dimensions and shape.
- The force exerted on any item.
- The surface's ability to adhere.
Now, for the same set of body and surface movement, sliding friction is often always less than static friction, as we have already discussed. Another important conclusion that follows from this is that the type of material that makes up the item and surface always determines the frictional force. Moreover, a sliding force is proportional to the normal force, or the load of the item, as previously explained. It was made clear in the preceding section that the sliding friction in the experiment would be constant regardless of which side of the block was resting on the table. As a result, the sliding friction is free of the region of contact for equal masses. Additionally unaffected by motion speed is the sliding friction.
Since sliding friction occurs to a great extent, there are no different examples. Due to chemical interactions, sliding friction between two surfaces generates heat. Depending on the surfaces' materials, the amount of heat generated can occasionally ignite a fire. The modern example of lighting a match stick is amazing. Men in the Stone Age lit fires with two stones. The result of rolling friction is much smaller than that of sliding friction, which makes it preferable to place an object on a wheel and transport it rather than push along due to the large degree of frictional force in sliding friction. The coefficient of rolling friction values is significantly lower than those for sliding friction.
Consider a vehicle parked on a sloped surface with a lower gradient. The car's wheels will start to rotate and start moving if there is no sliding friction. This is the reason that while parking on steep inclines, hand brakes are employed, and in extreme circumstances, big stones are put behind the tires. Due to its high level, sliding friction has a purpose in real life.
What is Rolling Friction?
Now, rolling resistance, also known as rolling friction or rolling drag, is the force that opposes the motion of a body as it rolls on a surface, such as a ball, tire, or wheel. It is mostly brought about by non-elastic effects, which means that not all of the energy required for the deformation (or movement) of the wheel, roadbed, etc., is restored when the pressure is released. Hysteresis losses (see below) and long-term (plastic) deformation of the object or surface are two examples of this (e.g. soil).
Take note that energy is also lost as a result of the friction between the wheel and the surface. Even though some researchers have included this term in their definition of rolling resistance, others argue that it should be treated separately because it is caused by the torque applied to the wheel and the subsequent slip between the wheel and the ground, also known as slip loss or slip resistance. Additionally, the term "rolling friction" is rather misleading because only the so-called slip resistance incorporates friction.
Now, according to experts, rolling resistance is often stated as a coefficient twice the normal force, which is similar to how sliding resistance is. In contrast to the coefficient of sliding friction, this friction coefficient is often much smaller.
Every vehicle with tires that are coasting will ultimately slow down due to rolling resistance, including that of the bearings, but a railway car with steel wheels traveling on rail tracks will roll much further than a bus with rubber tires running on tarmac or asphalt of the same mass. The (amount of) distortion of the wheels, the distortion of the roadbed ground, and movement beneath the surface are all factors that affect friction force.
Wheel diameter, load on the wheel, surface adhesion, sliding, and relative micro-sliding between the surfaces of contact are further significant elements. The material characteristics of the wheel or tire and the surface have a significant impact on the losses brought on by hysteresis. For instance, a steel railroad wheel on a steel rail will have less rolling resistance than a rubber tire on a paved road. Furthermore, compared to concrete, sand on the ground will provide more rolling resistance. Speed has no impact on the sole rolling resistance factor.
The rolling cylinder figure serves as an example of this fundamental idea. A pair of equal cylinders squeezed together results in a flat contact surface. Contact stresses are normal, or perpendicular to the contact surface when there is no surface friction. Consider a particle that goes through the contact patch from the right side, entering the contact region from the right, and exiting from the left side. The hysteresis effect prevents the rising vertical deformation at first. To prevent the two surfaces from touching, extra pressure is created. Later, it experiences less vertical deformation. The hysteresis effect again opposes this. In this instance, it lowers the pressure required to maintain the separation of the two bodies.
The resulting pressure distribution is moved to the right and is asymmetrical. The vertical force's (combined) axis of action no longer crosses through the cylinders' centers. This indicates that there is a moment that tends to slow the rolling action.
Rolling resistance is higher in materials having a big hysteresis effect, such as rubber than in materials with a moderate hysteresis effect, such as steel or silica, which bounce back more fully and quickly. To lessen low-frequency hysteresis without sacrificing traction, low-rolling resistance tires frequently substitute silica for carbon black in their tread compositions.
Main Differences Between Sliding Friction and Rolling Friction In Points
- A relationship between the size of small bumps on surfaces causes sliding friction. Rolling friction results from surface deformation.
- One type of friction is acceptable sliding friction. Rolling friction is a specific kind of friction rather than a resistive force. Understanding that friction is not the only form of resistive force is crucial.
- The architecture of the surface and the limited amount of warmth that is available also affect the coefficient, thus it cannot just be attributed to outside forces. The radius of the rolling piece, the depths at which it descends, the composition of the top layer, as well as other variables all affect the coefficient.
- Within the contact area, sliding friction works as a constant external component to halt relative motion. The goal of rolling friction is to prevent the wheel from rolling by producing a reverse torque.
Conclusion
Hence, now we got to know the differences between sliding friction and rolling friction in detail.
References
- Rolling resistance. (n.d.). Retrieved from WIKIPEDIA: https://en.wikipedia.org/wiki/Rolling_resistance
- Sliding Friction. (n.d.). Retrieved from Vedantu: https://www.vedantu.com/physics/sliding-friction
