← MAP Physics Lab
Skid & Traction
Explore how static friction allows a rolling tyre to grip the road, and what changes when the tyre begins to slide.
35%
Road surface
STATIC FRICTION
The tyre is rolling without slipping. Static friction supplies the braking force.
Braking force needed
2.2 kN
Maximum static friction
6.5 kN
Static friction can take any value from zero up to its maximum. Kinetic friction applies only once sliding begins.
Static friction:
Fs ≤ μsN
Maximum static:
Fs,max = μsN
Kinetic friction:
Fk = μkN
The point of tyre in contact with the road is not sliding.
Static does not mean stationary
The car and wheel are moving, but the tyre does not slide across the road at the point of contact.
The friction is therefore static.
If the braking demand becomes greater than the maximum possible static friction, the tyre begins to slide.
The friction then becomes kinetic.
Static friction increases as needed up to a maximum. Once sliding begins, kinetic friction is usually smaller.
Simplified teaching model using a 1000 kg vehicle and g = 10 m/s². The coefficients of friction are illustrative values.