Friction Force
Reference from the original Physics I textbook.
- Friction Force
Friction is a contact force that opposes relative sliding or the tendency to slide between surfaces. Kinetic friction can convert mechanical energy into thermal energy; static friction need not dissipate energy.
- Related Glossary Terms
Free body diagrams↗, Friction Force Equation, Heat Loss Equation, Kinetic Friction↗, Non-Conservative Force, Normal Force, Static Friction
- Index
Reviewed physics notes (1)
These corrections keep the original lesson’s purpose while fixing errors in the source edition.
- Friction need not oppose an object’s motion in the ground frame, and static friction need not produce heat. — Reference 1
Glossary and deeper reading · 3 refreshers
These editorial refreshers supplement the reading. Definitions and examples are added guidance; original source wording and recorded answers remain in their original context.
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Force
A force describes an interaction that can change an object’s momentum. It is a vector measured in newtons, so both size and direction matter when forces are added. For example, a rope can pull a cart while the floor exerts friction in another direction.
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Free-body diagram
A free-body diagram shows the external forces acting on one selected object or system. Each arrow names a real interaction, and its direction is the direction of that force. For example, a book resting on a desk has a downward gravitational force and an upward normal force; velocity is not an extra force arrow.
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Kinetic friction
Kinetic friction acts between surfaces that slide relative to one another. It opposes their relative slipping and is often modeled with magnitude equal to the kinetic-friction coefficient times the normal force. For example, a rapidly moving belt can exert forward kinetic friction on a slower box sliding on it.