What is the SI unit for speed   

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The SI system is based on seven base units. These are defined as the units for length (meter), mass (kilogram), time (second), current (ampere), temperature (kelvin), amount of substance (mole) and luminous intensity (candela). All other SI units are combinations of these seven units and are thus called derived units.

We see that speed is not one of the base units. So we must breakdown speed until we find a relationship that describes speed using the base quantities.

Speed is a measure of how fast something is moving, or rather, how much distance is the object moving per unit time. 

`Speed = (distance)/(time)`

Distance is a length. Since length and time are base quantities, we can then deduce that the SI unit for speed is the SI unit of length (meters) over the SI unit of time (seconds), or `(meters)/(seconds)`  which is abbreviated m/s.

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