Name: sliding friction between moving surfaces
Uploaded: 2023-09-22T11:49:28.000Z
Duration: 1 min 26 s
Channel: JoVE

Consider a truck trying to move a stationary car. As the truck tries to pull the car, static friction is created at the contact surface.
When the applied force exceeds the limiting static frictional force, the frictional force at the interface decreases to a lesser value, called the kinetic frictional force. The car then begins to slide with increasing speed.
The magnitude of kinetic frictional force is proportional to the normal force, with the proportionality constant being the coefficient of kinetic friction.
The continued breakdown of the interface is responsible for creating kinetic friction, which resists the car&#39;s motion.
As the car&#39;s velocity increases, initially, the kinetic friction decreases slowly. However, at higher velocities, it shows a significant decrease.
The angle between the kinetic friction force and the resultant normal force is the angle of kinetic friction. It is always less than or equal to the maximum static friction angle.
The coefficient of kinetic friction depends on the surface&#39;s condition and the relative velocity between the two surfaces.

kinetic friction

Consider a truck trying to pull a stationary car. As the truck exerts a force on the car, static friction is created at the point of contact between the two surfaces. This frictional force resists the car&#39;s movement and keeps it at rest. However, when the applied force by the truck surpasses the limiting static frictional force, an interesting phenomenon occurs. The frictional force at the interface reduces to a lower value, known as the kinetic frictional force. At this point, the car begins to slide and its speed increases.
Kinetic friction, also referred to as dynamic friction or sliding friction, is the force that opposes the relative motion between two objects in contact while they are moving. It acts parallel to the contact surface and in the opposite direction of the motion. In the example of truck and car, kinetic friction is responsible for resisting the car&#39;s motion as it starts to slide.
The magnitude of the kinetic frictional force is directly proportional to the normal force acting on the objects with a proportionality constant, denoted as the coefficient of kinetic friction, which is a dimensionless quantity that depends on the properties and condition of the surfaces in contact.
As the car starts to slide with increasing speed, the interface between the truck and the car undergoes a continuous breakdown. This process is responsible for generating kinetic friction, which opposes the car&#39;s motion. Interestingly, the magnitude of kinetic friction does not remain constant as the car&#39;s velocity increases. Initially, kinetic friction decreases slowly, but it experiences a more significant drop at higher velocities.
The angle between the kinetic friction force and the resultant normal force is called the angle of kinetic friction. This angle is always less than or equal to the maximum static friction angle. Notably, the angle of kinetic friction depends on the materials and conditions of the surfaces in contact.
Various factors, including the condition of the contacting surfaces and the relative velocity between them, influence the coefficient of kinetic friction. Rougher surfaces tend to have higher coefficients of kinetic friction, while smoother surfaces exhibit lower values. Also, lubricants or contaminants can alter the coefficient of kinetic friction by changing the surface conditions.

Kinetic Friction

Consider a truck trying to pull a stationary car. As the truck exerts a force on the car, static friction is created at the point of contact between the ...

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JoVE Core

Mechanical Engineering

Unit 1

Friction

KEY TERMS AND CONCEPTS

sliding friction between moving surfaces

Kinetic friction is the sliding friction that acts when two surfaces move against each other. It opposes relative motion and acts parallel to the contact surface, in the opposite direction of travel. In the truck and car example, the car first stays still because static friction holds it in place.

When the truck’s force becomes greater than the limiting static frictional force, the friction at the contact surface drops to a lower value. The car then begins to slide, and its speed increases. At that point, kinetic friction resists the motion of the sliding car.

The size of the kinetic frictional force depends on the normal force, which is the force pressing the surfaces together. It is proportional to that normal force through the coefficient of kinetic friction. This coefficient is a dimensionless value, and it depends on the materials and the condition of the surfaces in contact.

As the car keeps sliding, the interface between the truck and the car continues to break down. That breakdown helps produce kinetic friction. The force does not stay exactly constant as speed rises. It decreases slowly at first, then drops more at higher velocities.

The angle of kinetic friction is the angle between the kinetic friction force and the resultant normal force. It is always less than or equal to the maximum static friction angle. This angle also depends on the materials and surface conditions. Rougher surfaces usually have higher coefficients of kinetic friction, while smoother surfaces have lower values. Lubricants or contaminants can also change the coefficient by altering the surface conditions.

Sliding Friction Between Moving Surfaces

dry friction

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static friction

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Kinetic friction is the sliding friction that acts when two surfaces move against each other. It opposes relative motion and acts parallel to the contact surface, in the opposite direction of travel. In the truck and car example, the car first stays still because static friction holds it in place. When the truck’s force becomes greater than the limiting static frictional force, the friction at the contact surface drops to a lower value. The car then begins to slide, and its speed increases. At...

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key terms and concepts

Learn how kinetic friction acts during sliding motion, why it changes as surfaces move, and how surface type, normal force, and lubrication affect it.

Sliding Friction Between Moving Surfaces | JoVE K12

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mechanical engineering

Sliding Friction Between Moving Surfaces

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