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friction

FRIK-shun /ˈfrɪkʃən/

nounB1SATACTTOEFLIELTS

GeneralTechnicalAcademic

The resistance that one surface or object encounters when moving over another.

Friction is a force that always opposes relative motion between two surfaces in contact. It can be static (preventing motion from starting) or kinetic (resisting ongoing motion). It converts kinetic energy into thermal energy (heat).

The story behind the word. Friction comes from the Latin verb 'fricare', meaning 'to rub'. In the 16th century, it was used in medical contexts to describe the rubbing of the skin with oils or ointments. By the 18th century, physicists like Amontons and Coulomb formalized the physical laws of friction, turning a medical term into a cornerstone of mechanical engineering.

Word relationships

resistance: Resistance is a broad term for any opposing force, while friction is specifically the resistance generated by two solid surfaces rubbing against each other.

lubrication: Lubrication is the application of a substance to reduce friction and allow smooth sliding.

Commonly confused with

traction: Traction is the specific, useful application of friction that allows a wheel or shoe to grip a surface without slipping.

Word family

frictional (adjective): Relating to or caused by friction.
frictionless (adjective): Having no friction; perfectly smooth.

Collocations

coefficient of friction
static friction
kinetic friction
reduce friction

Idioms & expressions

rub someone the wrong way

Example sentences

"Friction between the brake pads and the spinning brake rotors slows the vehicle down, converting kinetic energy into heat." A car maintenance guide
"Engineers use lubricants to minimize friction in the engine, which improves fuel efficiency and reduces wear." A physics lecture on efficiency

Memory hook

Think of 'friction' as 'rubbing' your hands together on a cold day to create heat. The 'fr' in friction is like 'freezing' hands rubbing together. Friction is the rub that slows things down.

When not to use

Do not use friction to describe resistance through a fluid like air or water; use 'drag' or 'viscosity' instead.

Fun facts

Without friction, you wouldn't be able to walk; your feet would simply slide in place like you were on perfectly frictionless ice.
Violin bows rely on friction; the horsehair is coated in sticky rosin to grip the strings, pulling them to create sound waves.