II.1.3. Measurement units. Multiples and submultiples

Setting of the measurement units is done through international conventions.

At the international level it was agreed to have a unique system of quantities and measurement units, called the International System of Sizes and Units (the abbreviation being SI). It has been applied in Romania since 1960.

To express that the unit of length in the SI is meter we write:

and it reads the measurement unit of length in the International System is the meter.

To express that the unit of time interval in SI is the second we write:

and it reads the measurement unit for time interval in the International System is the second.

🔦 Remark:

During the study of physics you will learn many physical parameters and their units in SI. You also need to know the values of multiples and submultiples that apply to all measurement units. In addition to those that are basic, there are other larger multiples, or other smaller submultiples.

Measurement units multiples - are greater than that unit whenever their value show:

Measurement units submultiples - are smaller than that unit whenever their value show:

🔦 Remark:

When we have to transform from a submultiple or multiple to the base unit, we copy the given value, then instead of the symbol of the multiple or submultiple we replace its value (preferably as a fraction, in submultiples) and copy the remaining unit (see the examples in the table).

Remember, when we have a number multiplied by 10, 100, 1000, etc., the comma of the number moves to the right over as many digits as we have zeros.

Example:

• 0,7 ∙ 1000, we move the comma to the right over 3 digits and in the free places we put zero.

🔦 Remark:

Remember, when we have a number divided by 10, 100, 1000, etc., the comma of the number moves to the left over as many digits as we have zeros.

Example:

• 43/1000 we move the comma to the left over 3 digits and in the free places we put zero.

To characterize a physical size we need to show it:

The symbol.

Definition or calculation formula (there are parameters that do not have a formula and are only determined directly by measurement using a measurement instrument; for example: length, duration, temperature etc.).

Measurement units (the fundamental one or in the International System and the derived ones).

Measurement instruments (there are few physical parameters for which there are no measurement instruments; they are determined only indirectly by calculation using a formula; for example: area, mechanical strength, heat etc.).