Rubber Friction Coefficient
What is the friction coefficient of rubber?
Friction is the force that resists the relative motion of two solid surfaces sliding or rolling over each other. The friction coefficient is a numerical value that characterises this resistance. It defines the relationship between two surfaces in contact, resulting from the normal force pressing them together and the tangential force causing or attempting to cause motion. The unit of the friction coefficient is derived from force (newton, N).
What is the static friction coefficient?
Static friction occurs between two surfaces that are in contact but not moving relative to one another. The force of static friction can increase up to a maximum value (T max). When an applied force (F) on an object exceeds this maximum value, the object will begin to move. This is because the maximum static friction force is no longer sufficient to counteract the applied force. The ratio of the maximum friction force (T max) to the normal force (F) is called the static friction coefficient. This value depends on the materials in contact.
Examples of static friction include glass on glass, rubber tyres on asphalt, and steel on steel.
What is the kinetic friction coefficient?
Kinetic (or dynamic) friction occurs between two surfaces that are sliding relative to each other. Kinetic friction is divided into two categories: physically dry and technically dry friction. It is essential to consider the mechanical and physical properties of the surfaces in contact, including surface roughness, finish quality, possible deformations, and the materials involved. Generally, the kinetic friction coefficient is lower than the static friction coefficient.
What is the friction coefficient of rubber?
Both static and kinetic friction coefficients are used to measure the resistance between two objects in contact.
The coefficient varies depending on:
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the surface material in contact with the rubber
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the static friction coefficient
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the kinetic friction coefficient
For example:
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Rubber on rubber: static coefficient = 1.15
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Rubber on asphalt: static coefficient = 0.9
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Rubber on concrete: static coefficient = 1.0
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Rubber on tool steel: static coefficient = 0.86
According to physicist Guillaume Amontons, who formulated the laws of friction, the friction force is generally independent of the contact surface area, except when changes in contact area affect the pressure distribution.
Types of Solid Friction: Sliding and Rolling
Friction types are categorised by contact conditions (dry, fluid, mixed, boundary) and motion type (sliding vs. rolling friction). Sliding friction refers to the resistance encountered when two surfaces move or attempt to move across each other. Its coefficient is a dimensionless value. Rolling friction (or rolling resistance) occurs when one object rolls over another surface.
Common Effects of Friction
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Beneficial resistance in motion (e.g., braking, grip in conveyor belts, or clutches)
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Unwanted energy loss due to resistance
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Surface wear
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Heat generation
Friction Coefficient Table
What does a low friction coefficient mean?
A coefficient of 0 means there is no friction between the two objects. The lower the coefficient, the less grip exists between the surfaces, and they slide more easily against one another.
Can the friction coefficient be higher than 1?
Yes, the friction coefficient can be greater than 1. Friction force is calculated as the product of the static or kinetic friction coefficient and the normal force acting on the object. Only certain material combinations produce a friction coefficient above 1 (e.g., rubber on rubber, or aluminium on aluminium with values between 1.05–1.35).
At Power Rubber, we offer a wide range of high-quality rubber products. If you have any questions, feel free to contact our experts for assistance.
