Measuring Movement Over Time
Speed (a scalar quantity) and Velocity (a vector quantity) are simply a measure of distance divided by time.
Street and Highway Speeds
- km/h (Kilometers per hour): Used for road speed limits in almost every country on Earth.
- mph (Miles per hour): Standard on roads in the United States, the UK, and several Caribbean nations.
Maritime and Aviation
- Knot (kn): One nautical mile per hour. A nautical mile is precisely 1,852 meters. Knots are universally used in maritime navigation and aviation regardless of the country.
Scientific and Supersonic Speeds
- m/s (Meters per second): The SI derived unit of speed.
- Mach Number: A dimensionless ratio of the speed of an object to the speed of sound in the surrounding medium. Mach 1 at sea level is approximately 343 m/s (767 mph).
- Speed of Light (c): The absolute speed limit of the universe, exactly 299,792,458 m/s in a vacuum.