Speed measures distance traveled per unit time, expressed in units like kilometers per hour (km/h), miles per hour (mph), meters per second (m/s), feet per second (ft/s), or knots (nautical miles per hour). For example, 100 km/h equals 27.78 m/s (100,000 m ÷ 3,600 s) or 62.14 mph (100 ÷ 1.60934). Different domains prefer specific units: automobiles use km/h (metric countries) or mph (US/UK), physics uses m/s (SI standard), aviation/maritime use knots. Understanding conversion factors enables cross-domain communication and accurate calculations.
SI base unit for speed is meters per second (m/s), derived from base units of length (meter) and time (second). All other speed units convert to m/s: 1 km/h = 0.277778 m/s, 1 mph = 0.44704 m/s, 1 knot = 0.514444 m/s, 1 ft/s = 0.3048 m/s. Knots are unique—based on nautical miles (1.852 km), originally defined as one minute of latitude. Aviation and maritime navigation use knots because nautical miles relate directly to latitude/longitude, simplifying navigation calculations without unit conversions.
Velocity differs from speed by including direction (velocity is a vector, speed is scalar magnitude). In physics, velocity specifies direction: 'moving north at 50 m/s' vs speed 'traveling at 50 m/s'. For practical conversions, speed and velocity use identical units—only vector components (northward velocity, eastward velocity) require directional notation. When converting speeds, context determines precision: highway speeds need 1 decimal (100.0 km/h), ballistics need high precision (850.50 m/s), casual estimates tolerate rounding (≈60 mph).
