Friction

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Friction Noun

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[frik-shun]

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Friction

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A force that opposes the motion or tendency of motion between two surfaces that are in contact with each other.

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Example: This diagram shows a car moving onto a rough surface, illustrating that friction is a force that acts in the opposite direction of an object's motion.

Front

Static Friction Noun

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[stat-ik frik-shun]

Back

Static Friction

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The frictional force that prevents two surfaces from sliding past each other when there is no motion between them.

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Example: This diagram shows an applied force trying to move a box, while static friction is the opposing force that keeps the box from moving.

Front

Kinetic Friction Noun

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[ki-net-ik frik-shun]

Back

Kinetic Friction

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The frictional force exerted on one surface by another when the two surfaces are moving relative to each other.

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Example: A skier moving down a slope experiences kinetic friction, a force that acts in the opposite direction of their motion, slowing them down.

Front

Coefficient of Static Friction Noun

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[koh-uh-fish-uhnt ov stat-ik frik-shun]

Back

Coefficient of Static Friction

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A unitless value representing the relative difficulty of initiating sliding motion between two surfaces, used to calculate maximum static friction.

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Example: This diagram shows the forces on a stationary block, where the frictional force opposes the applied force, preventing movement. The coefficient of static friction relates this friction to the reaction force.

Front

Coefficient of Kinetic Friction Noun

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[koh-uh-fish-uhnt ov ki-net-ik frik-shun]

Back

Coefficient of Kinetic Friction

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A unitless value that relates the kinetic friction force to the normal force for two surfaces already in motion.

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Example: This diagram shows the forces on a moving skier, including the friction force opposing motion. The symbol μk represents the coefficient of kinetic friction.

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Normal Force Noun

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[nor-muhl fors]

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Normal Force

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The support force exerted by a surface on an object, which acts perpendicular to that surface.

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Example: A surface exerts an upward push, called the normal force, on an object resting on it, which counteracts the downward pull of the object's weight.

Front

Microwelds Noun

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[mahy-kroh-weldz]

Back

Microwelds

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Microscopic bumps and ridges on surfaces that can interlock, creating friction when the surfaces are in contact.

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Example: This diagram shows that even smooth surfaces are rough at a microscopic level. The bumps and grooves interlock, creating "microwelds" that cause friction.

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Force Noun

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[fors]

Back

Force

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A push or a pull exerted on an object that has both magnitude and direction, causing a change in motion.

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Example: This image displays eight different types of forces. The top-left example illustrates friction, a force that opposes the motion of a sleigh sliding on snow.

Front

Rolling Friction Noun

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[rohl-ing frik-shun]

Back

Rolling Friction

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The resistive force that occurs between a rolling object and the surface it rolls on, opposing the rolling motion.

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Example: This diagram uses a tire and opposing arrows to show that rolling friction is a force that acts against the direction of an object's motion.

Front

Air Resistance Noun

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[air ri-zis-tuhns]

Back

Air Resistance

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A type of fluid friction that opposes the motion of objects as they move through the air.

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Example: This image compares a falling feather and coin to show that air resistance, a type of friction, has a greater effect on objects with a larger surface area.