Absolute meter-kilogram-second system
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The absolute meter-kilogram-second system is a system of mechanical units. The meter is the base unit of length or distance, the kilogram is chosen to be a unit of mass, and the second is the base unit of time. All other mechanical quantities, and specifically force, are expressed in terms of combinations of these three units. In absolute systems, Newton's second law is expressed as F = ma, and since acceleration is the second derivative of a distance with respect to time, if the unit of length or distance is denoted by L, the unit of mass by M, and the unit of time by T, the unit of force becomes a derived unit of dimensions MLT^{−2}, in this case kilogram·metersecond^{2}, which is known as the newton.
Base |
force, length, time | weight, length, time | mass, length, time | |||||
---|---|---|---|---|---|---|---|---|
Force (F) | F = m·a = w·ag | F = m·ag_{c} = w·ag | F = m·a = w·ag | |||||
Weight (w) | w = m·g | w = m·gg_{c} ≈ m | w = m·g | |||||
System | BG | GM | EE | M | AE | CGS | MTS | SI |
Acceleration (a) | ft/s^{2} | m/s^{2} | ft/s^{2} | m/s^{2} | ft/s^{2} | gal | m/s^{2} | m/s^{2} |
Mass (m) | slug | hyl, also called “metric slug” or “TME” | lb_{m} | kg | lb | g | t | kg |
Force (F) | lb | kp | lb_{F} | kp | pdl | dyn | sn | N |
Pressure (p) | lb/in^{2} | at | PSI | atm | pdl/ft^{2} | Ba | pz | Pa |
International System of Units (SI)Edit
The SI is basically an example of an absolute meter-kilogram-second system, but with a number of additional units, which are used in decribing quantities outside of mechanics, to complete the system.
SI base units | ||
---|---|---|
Name | Symbol | Quantity |
kilogram | kg | Mass |
second | s | Time |
meter | m | Length |
ampere | A | Electrical current |
kelvin | K | Temperature |
mole | mol | Amount of substance |
candela | cd | Luminous intensity |
See also
ReferencesEdit
- ↑ Lindeburg, Michael, Civil Engineering Reference Manual for the PE Exam
- ↑ Wurbs, Ralph A, Fort Hood Review Sessions for Professional Engineering Exam, http://engineeringregistration.tamu.edu/tapedreviews/Fluids-PE/PDF/Fluids-PE.pdf, retrieved October 26, 2011