Speed is the rate of change in position of a moving quanity, without factoring direction into the equation. Walk forwards or backwards at 2 meters per second, and your speed is just that: 2 m/s. Velocity is speed in the context of direction. Say you were walking backwards again: your velocity would be negative 2 m/s, although your speed would still be positive.
For most science applications, the SI unit for speed and velocity is meters per second (m/s), although kliometers per hour (km/h) are sometimes used when measuring the speed of vehicles. The English system usually expresses speed as miles per hour (mph) or sometimes feet per second (ft/s), while marine vessels typically use knots, or nautical miles per hour.
Conversions are performed by using a conversion factor. By knowing the conversion factor, converting between units can become a simple multiplication problem:
S * C = E
Where S is our starting value, C is our conversion factor, and E is our end converted result.
To simply convert from any unit into meters per second, for example, from 5 mph, just multiply by the conversion value in the right column in the table below.
5 mph * 0.44704 [ (m/s) / (mph) ] = 2.2352 m/s
To convert from m/s into units in the left column divide by the value in the right column or, multiply by the reciprocal, 1/x.
2.2352 (m/s) / 0.44704 [ (m/s) / (mph) ] = 5 mph
To convert among any units in the left column, say from A to B, you can multiply by the factor for A to convert A into meters per second then divide by the factor for B to convert out of Pascals. Or, you can find the single factor you need by dividing the A factor by the B factor.
For example, to convert from miles per hour to kilometers per hour inch you would multiply by 0.44704 then divide by 0.2777778. Or, multiply by 0.44704/0.27777778 = 1.6093439. So, to convert directly from mph to km/h (kph), you multiply by 1.6093439.
|To Convert from
|and Convert to
( m/s )
( m/s / Unit )
|centimeter per minute||cm/min||meter per second||0.0001667|
|centimeter per second||cm/s||meter per second||0.01|
|foot per hour||ft/h||meter per second||8.46667E-05|
|foot per minute||ft/min||meter per second||0.00508|
|foot per second||ft/s||meter per second||0.3048|
|inch per minute||in/min||meter per second||0.000423333|
|inch per second||in/s||meter per second||0.0254|
|kilometer per hour||km/h (kph)||meter per second||0.2777778|
|kilometer per second||km/s||meter per second||1000|
|knot (nautical mi/h)||kn||meter per second||0.5144444|
|knot (UK)||kn||meter per second||0.5148|
|meter per hour||m/h||meter per second||0.0002777778|
|meter per minute||m/min||meter per second||0.01667|
|meter per second||m/s||meter per second||1|
|mile per hour||mi/h (mph)||meter per second||0.44704|
|mile per minute||mi/min||meter per second||26.8224|
|mile per second||mi/s||meter per second||1609.344|
|speed-of-light (vacuum)||c||meter per second||299792458|
|yard per hour||yd/h||meter per second||0.000254|
|yard per minute||yd/min||meter per second||0.01524|
|yard per second||yd/s||meter per second||0.9144|
The National Institute of Standards and Technology (NIST) - The NIST Guide for the use of the International System of Units - Appendix B, subsections B.8 Factors for Units Listed Alphabetically and B.9 Factors for units listed by kind of quantity or field of science.
Lide, David R., Daniel (Editor-in-Chief). CRC Handbook of Chemistry and Physics, 89th Edition New York, NY: CRC Press, p. 1-28, 2008.
Wikipedia contributors. "Conversion of units" Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, last visited 26 Jun. 2011.
How Many? A dictionary of units of measurement at http://www.unc.edu/~rowlett/units/