What Is Rolling Friction?

Rolling friction. When an object makes non-sliding rolling or has a tendency to roll on the surface of another object, the blocking effect on rolling caused by the deformation of the two objects in the contact part is called rolling friction. Its essence is static friction.

Chinese name: Rolling friction
Foreign name: (Rolling friction

Features: Non-sliding scrolling or scrolling trend
Nature: Obstruction

Introduction to rolling friction

Rolling friction is generally measured by resistance torque. The magnitude of its force depends on the nature of the object, the shape of the surface, and the rolling

Rolling friction during dragging Animal weight is related. Rolling friction is actually a torque that hinders rolling. When an object rolls on a rough surface, if it is no longer subject to power or dynamic torque, its motion will gradually slow down until it stops. In this process, in addition to the gravity and elasticity of rolling objects, static friction is generally encountered at the contact parts. Due to the deformation of the contact between the object and the plane, the object sinks into the support surface due to gravity, and the object itself is compressed and deformed. When the object rolls forward, the support surface in front of the contact bulges, so that the support surface acts on the object. The action point of the combined elastic force N moves forward from the lowest point. It is this elastic force that generates a moment that prevents the object from rolling relative to the center of mass of the object. This is rolling friction. For junior high school students, they have not mastered the concept of torque, so they should not speak of rolling friction as a kind of friction, but only say that an object is hindered from rolling when it is rolling on another object. The essence of rolling friction is static friction.

In simple terms, the pressure deforms the object, and the surface around the object becomes a small slope, which is equivalent to a small slope when rolling (there are small slopes on both sides). The gravitational force generates a sliding force when going up a small slope, which is relative to the small ball as resistance.

Characteristics of rolling friction

The rolling state of an object is related to the contact surface. When a rolling object rolls on the contact surface or has a tendency to roll, both the object and the contact surface will deform. Its deformation can be divided into contact surface deformation without rolling object deformation (the object is called a rigid body at this time), contact surface deformation (the contact surface is called a rigid surface at this time) and rolling object deformation, the contact surface and rolling There are four situations in which the object is not deformed and the contact surface and the rolling object are deformed.

Rolling friction The rolling object is a rigid body and the contact surface is deformed

The gravitational force G and the supporting force N received by the rolling object while stationary on the horizontal contact surface are on the same vertical line. When the rolling object rolls forward, it acts with the front protrusion, the fulcrum moves forward to O , and the force on the contact surface increases to N . N produces two effects: one is N perpendicular to the direction of the contact surface, which competes with G ; the other is the static friction force f along the direction of the contact surface, which prevents the ball from sliding forward, as shown in FIG. 3.

Rolling friction

Obviously, the gravity G and the supporting force N generate a force moment M resistance, the effect of which is to hinder the rotation of the object. Let O 'deviate from the line of gravity action by , then M resistance = N .

If the vertical distance from the component f of N in the direction of the contact surface to O is r and O is the axis of rotation, the moment is balanced when the object rolls at a constant speed, then fr = N.

The roller of the roller can be reduced to this kind of problem when it is rolling the soil subgrade.

The rolling friction contact surface is rigid, and the rolling object is deformed

When the contact surface is not deformed and the rolling object is deformed, the rolling of the object is essentially a flip after deformation, but the fulcrum O moves forward. Similarly, at this time, the moment of gravity of the gravity G and the supporting force N is the resistance moment of the object rolling, and M resistance = N .

Car and bicycle tires can be reduced to this type of problem when driving on cement roads.

Rolling friction rolling objects and contact surfaces are rigid

If neither the rolling object nor the contact surface is deformed, the gravity and supporting force of the object at this time are collinearly balanced, that is, G = N, = 0, r = 0, rolling resistance moment M resistance = 0, f = 0 No rolling friction effect.

This is ideal, but motions like train wheels on rails can be reduced to this type of problem.

Deformation of rolling objects and contact surfaces

The deformation of both the rolling object and the contact surface is the most common. Although this situation is very complicated, it is between the first and second cases. According to the "law of the two sides", the same conclusion can be obtained, M resistance = N ,. However, when the deformation of the rolling object is relatively large compared to the contact surface, it can be simplified to the first case; when the deformation of the contact surface is relatively large, it can be simplified to the second case.

About rolling friction

Why is it harder to ride a bicycle when it is flat?

Everyone may have experienced this, and it feels very difficult to ride when the bike is flat. What is the reason for this? That's where I started my little exploration.

To understand why it's difficult to ride when you're out of gas, you must first understand how the bike works. When a person pedals a bicycle, the chain wheel rotates, and the flywheel that drives the rear wheel through the chain rotates, so that the rear wheel also rotates. At this time, the tire has a backward static friction force facing the ground. As shown in Figure 3, the ground also has a forward static friction force against the rear wheel. This force is the driving force of the car. As the wheels roll on the ground, there must be rolling friction. However, the middle school has not studied in-depth about rolling friction, and the impact on rolling friction is not very clear, so you should check the information to find out.

It can be known by consulting the data that when an object rolls on the surface of another object, it is subject to the resistance of the contact surface, which is called rolling friction. The condition under which rolling friction occurs is that the rolling contact between the rolling object and the plane must be deformed. The picture shows the deformation.

The deformation is characterized by the formation of protrusions in front of rolling objects. In this way, the horizontal component force of the supporting force hinders the translation, and the vertical component force hinders the rotation, so rolling friction is generated.

Then come back to the bike. As you already know, static friction provides power, so the only reason for an airless bicycle to be difficult to ride is only rolling friction. When a bicycle wheel is pressed on the ground, elastic deformation will definitely occur, and the ground will also deform, but the deformation of the wheel is the main. When the bicycle is out of air, the deformation of the wheel increases, making the convex part of the front of the wheel more convex, increasing the rolling friction torque, and making the bicycle difficult to ride.