SUMMARY

Physics is an experimental science in which measurements made must be expressed in units.
All physical quantities have a magnitude (size) and a unit
The SI unit of length, mass, time, temperature, electric current, amount of substance and luminous intensity are metre, kilogram, second, kelvin, ampere, mole and candela respectively.
Units of all mechanical, electrical, magnetic and thermal quantities are derived in terms of these base units.
Screw gauge, vernier caliper methods are available for the measurement of length in the case of small distances.
Parallax, RADAR methods are available for the measurement of length in the case of long distances
The uncertainty in a measurement is called error. The accuracy of a measurement is a measure of how close the measured value is to the true value of the quantity.Every accurate measurement is precise but every precise measurement need not be accurate.
When two or more quantities are added or subtracted, the result can be as precise as the least of the individual precisions. When the quantities are multiplied or divided, the result has the same number of significant figures as the quantity with the smallest number of significant figures.
Dimensional analysis is used to perform quick check on the validity of equations.Whenever the quantities are added, subtracted or equated, they must have the same dimension. A dimensionally correct equation may not be a true equation but every true equation is necessarily dimensionally correct.