Measurement

Measurement is the comparison of a physical quantity with its standard unit, and it underlies every scientific study. Physics is fundamentally a quantitative science: a physicist's statements are backed by numbers, not just words. As Lord Kelvin put it, when you can express what you are talking about in numbers, you know something about it; when you cannot, your knowledge is meagre and unsatisfactory. This section builds up, from scratch, exactly what a 'physical quantity' and …