Coefficient of Friction Calculator
Calculate static and kinetic coefficients of friction for material pairs. Determine friction force, angle of repose, and compare with standard values per ASTM G115.
Engineering Formulas
Static Friction
Kinetic Friction
Angle of Repose
Engineering Notes
Assumptions
Common Mistakes
Frequently Asked Questions
What is the difference between static and kinetic friction?
Static friction acts on stationary objects and must be overcome to start motion. Kinetic (sliding) friction acts on moving objects and is generally lower. Static friction is typically 20–40% higher than kinetic friction for the same materials.
What is the angle of repose?
The angle of repose (or friction angle) is the steepest angle at which an object remains stationary on an incline. It equals tan⁻¹(μs). For μs = 0.74 (steel on steel), the angle of repose is about 36.5°.
How does lubrication affect friction?
Lubrication significantly reduces friction by creating a fluid film between surfaces. Steel on steel drops from μs = 0.74 (dry) to μs = 0.16 (lubricated).
What is rolling friction?
Rolling friction (or rolling resistance) occurs when an object rolls over a surface. It is typically 10–100 times smaller than sliding friction, which is why wheels and ball bearings are efficient.
What factors affect the coefficient of friction?
Key factors include: material pairing, surface roughness/ finish, temperature, presence of contaminants or lubricants, normal load, and sliding velocity.
Why do rubber on concrete have high friction?
Rubber deforms to conform to concrete surface irregularities, creating high adhesion and hysteresis losses. Dry rubber on concrete has μs ≈ 1.0 — one of the highest common material pairs.
What is the friction coefficient of ice?
Ice has very low friction — steel on ice has μs ≈ 0.03, making it one of the slipperiest common material pairs. Skates work by melting a thin water layer under the blade.
How is friction coefficient measured?
Common methods include: inclined plane (measure angle when sliding starts), direct pull (measure force to slide a block), and tribometer testing per ASTM G115.