Systems of Units Measurement

The CGS (centimeter, gram, second) system

• Length is measured in centimeters, mass is measured in grams and time is measured in seconds.
• Thus centimeter, gram and seconds are the fundamental units of measurement in the CGS system.

MKS (meter, kilogram, second) system 

• Unit of measurement for length is meter, for mass it is kilogram and for time it is seconds.
• Thus in this system meter, kilogram and seconds are fundamental units of measurement.
• This system was used in France and number of other European countries.

FPS (foot, pound, second) system

• Unit of measurement for length is foot, for mass it is pound and for time it is second.
• This system is used commonly in Britain and the countries that were under its rule.

SI system

• In SI system length is measured in meter, mass in kilogram and time in seconds
• The SI system or the International system of standards has now replaced all the systems of measurement.

Fundamental & Derived Units

Fundamental Units

• The units of fundamental physical quantities (length, mass & time) are called fundamental units.
• These units can neither be derived from one another nor can be resolved into any other units.
• They are independent of one another.

Derived Units

• Are the units of physical quantities which can be expressed in terms of fundamental units
• Unit of area can be an example for derived unit. If L is the length of square then L x L = L² is its area. Similarly, the volume of a cube is L x L x L = L³ cubic area.

Scalar and Vector Quantity

Scalar Quantities 

• Measurements that strictly refer to the magnitude of the medium – absolutely no directional components
• Everything from tons to ounces to grams, milliliters, seconds & volume are all scalar quantities, as long as they are applied to the medium being measured and not the movement of the medium.
• Two more commonly used scalar quantities in physical calculations are speed and temperature. As long as they are not associated with a directional movement, they remain scalar quantities.

Vector Quantities

• Refers to both the direction of the medium’s movement as well as the measurement of the scalar quantity.
• Increase/Decrease in Temperature – The measurement of the medium’s temperature is a scalar quantity; the measurement of the increase or decrease in the medium’s temperature is a vector quantity.
• Velocity – The measurement of the rate at which an object changes position is a vector quantity. For example: If a person quickly moves one step forward and then one step backward there would certainly be a lot of activity; but, there would be “zero velocity.”