Viscosity
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Definition
Viscosity is a fluid's resistance to deformation or flow, quantifying internal friction between fluid layers; dynamic viscosity is measured in pascal-seconds (Pa·s) or centipoise (cP).
Explanation
Water at 20°C has a dynamic viscosity of about 1 cP; honey is roughly 2,000–10,000 cP; glass is sometimes cited humorously as extremely viscous, though it is actually an amorphous solid. Viscosity decreases with temperature in liquids (engine oil thins when hot), which is why multi-grade motor oils (e.g., 10W-40) are formulated to maintain consistent viscosity across temperature ranges.
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RELATED TERMS
Torque
Torque is the rotational equivalent of force, equal to the applied force multiplied by the perpendicular distance from the pivot point, measured in newton-meters (N·m) or pound-feet (lb·ft).
Stress
Stress is the internal force per unit area within a material resulting from externally applied forces, measured in pascals (Pa) or pounds per square inch (psi).
Strain
Strain is the dimensionless ratio of a material's deformation (change in length) to its original length under applied stress: ε = ΔL/L₀.
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Tensile Strength
Tensile strength is the maximum stress a material can withstand while being stretched before it fractures, measured in megapascals (MPa) or pounds per square inch (psi).