Key Difference – Sliding vs Rolling friction
The key difference between sliding and rolling friction is that, sliding friction can be considered as a type of friction while rolling friction cannot be considered as a friction. However, rolling friction is often misunderstood to be a type of friction by a lot of students. Let us first briefly discuss what is friction before analyzing the differences between sliding and rolling friction. In simple terms, Friction is the force resisting the relative motion of adjacent objects sliding against each other.
What is Sliding Friction ?
Sliding friction is easy to understand and a very common concept. In the real life, we cannot find a perfectly smooth surface. When an object slides on any surface, it experiences a backward force because of the relative motion between the two adjacent surfaces. Sliding friction always acts against motion. We can experience sliding friction when we try to slide an object such as a cupboard across a flat floor.Here, we do not have to work against gravity, so the resistance that we feel here is the sliding friction. Moreover for a static situation, applied force which tries to slide the object is always equal to the friction acting on the object. When we gradually increase the applied force, there comes a certain moment that the object start moving in the direction of the external force. The friction which acts against the motion remains constant thereafter. Since the object slides on the surface, we can rename the friction as sliding friction.
What is Rolling Friction ?
The invention of the circular wheel is considered a milestone of the mankind. The idea to roll an object is the origin of the first wheel. Rolling friction is the force resisting the motion when an object rolls on a surface.When a body rolls perfectly upon a surface, theoretically there is no sliding friction between that object and surface. But in real life, due to the elastic properties, both body, and the surface undergo deformations. Think about a bicycle wheel on a tar carpet. There, we have a contact area rather than a contact point. At the contact area of the wheel and carpet, the wheel flattens out creating a small trench on the surface. The normal force is then distributed all over the contact area and reaction vectors gradually agglomerate at the trench against the motion. We can apply this concept to a train wheel on the rail as well. Steel causes less deformation than rubber. So, compared to the bicycle wheel, train wheel has a less rolling friction.
What is the difference between Sliding and Rolling friction?
Definition of Sliding and Rolling friction
Sliding friction: Sliding friction is the resistance created by two objects sliding against each other.
Rolling friction: Rolling friction is the force resisting the motion when an object rolls on a surface.
Characteristics of Sliding and Rolling friction
Type of Friction
Sliding friction: Sliding friction can be accepted as a type of friction.
Rolling friction: Rolling friction is a resistive force but not a type of friction. Keep in mind that, not all resistive forces can be called friction.
Type of resistance
Sliding friction: Sliding friction acts as a backhaul external force along the contact area to stop the relative motion.
Rolling friction: Rolling friction is a force which attempts to stop the rolling motion by generating a reverse torque.
Magnitude of resistance
Sliding friction: In most of the modern applications, the sliding friction between the shaft and the wheel is replaced by rolling friction by using ball bearings. One can find these bearings even in a bicycle wheel.
Rolling friction: Rolling friction is much less than sliding friction. It is easier to roll a wheel than to slide it along the ground. The wheel can go more distance when it slides.
References: http://www.phy.davidson.edu/fachome/dmb/PY430/Friction/rolling
Image Courtesy:“Friction diagram” by Polyvore.(Public Domain) via Wikimedia Commons
