7TH GRADE · POWERS
Friction force
Static, sliding and rolling friction in technology and everyday life.
The entire theory of the lesson is collected here; you can read it without an account. In interactive mode, the same theory appears as cards, followed by questions. with checking the answer and task, and progress is saved.
Basic Concepts
Static friction
A force that prevents the onset of relative sliding of contacting surfaces.
It is static friction that allows the foot to push off the ground without slipping and keeps the object on an inclined surface.
Rolling friction
Resistance to the movement of a rolling body is usually less than sliding friction under the same conditions.
Wheels reduce losses during transportation, but friction remains necessary for acceleration, braking and steering.
Sliding friction
A force directed against the relative sliding of surfaces and arising upon their contact.
Its value depends on the materials, the condition of the surfaces and the pressing force, and not directly on the contact area in a simple model.
Physical quantities
Friction force
The force of resistance to the relative movement of contacting surfaces.
Unit: newton ·
Friction coefficient
Dimensionless characteristics of a pair of contacting surfaces.
Unit: dimensionless quantity
Ground reaction force
The force with which a support acts on a body perpendicular to the surface.
Unit: newton ·
Lesson formulas
Sliding friction
The sliding friction force is equal to the friction coefficient multiplied by the support reaction force.
Condition: Model of dry sliding on a horizontal or specified support.
Related formulas
The same formulas in the reference, with symbols and units.
Tasks on the topic
Statements, answer options and the walkthrough.