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Length is measured using the following instruments.
(a). Metre Rule: A metre rule is a measuring device calibrated in centimetres (cm) with a range of 0 – 100cm. In using the metre rule, the eye must be fixed vertically on the calibration to avoid parallax errors.The smallest reading that can be obtained on a metre rule is 0.1cm (0.01cm).
(b). Callipers:these are used in conjunction with metre rule for measuring diameter of tubes, thickness of sheet, etc. The callipers are of two types –
The external calliper and
The internal calliper.
Fundamental quantities are physical quantities whose dimensions and units are not usually derived from other physical quantities. Basically, there are three fundamental quantities in mechanics. They include:
i) Mass: This is a fundamental quantity with dimension ‘M’, usually written in capital letter. The S.I. unit of mass is kilogramme (kg). Mass can also be measured in gramme (g), tonne (t), etc.
ii) Length: This is another fundamental quantity with dimension ‘L’, written in capital letter. The S.I. unit of length is metre (m). Length can also be measured in kilometre (km), centimetre (cm), inches (inch), feet (ft), etc.