The study of the relationships between physical quantities by identifying their units of measure and fundamental dimensions. It is used to convert from one set of units to others such as from miles per hour to meters per second, or from calories per slice of cake to kilocalories per whole cake.
What questions should have this tag? Questions which are related to the conversion between different units of measurement or fundamental dimensions (for example, converting speed from miles per hour to meters per second).
What are the basic methods? The factor-label method for converting units involves first creating a series of ratios equaling 1 from known identities and using those to multiply your input, cancelling dimensional units which appear both in the numerator and denominator until the result is in the desired dimensions.
For example, $10 \frac{\text{miles}}{\text{hour}} = 10\frac{\text{miles}}{\text{hour}}\times 5280\frac{\text{feet}}{\text{miles}}\times \frac{1}{3600}\frac{\text{hour}}{\text{second}} = 14.\overline{6}\frac{\text{feet}}{\text{second}}$
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