Physical Quantities and Measurement; SI Units
In physics we do not just say "big" or "heavy" — we measure, with a number and a unit.
Big Idea: A physical quantity is a property of a body or a phenomenon that we can measure. Every measurement has two parts that always go together: a number (how many) and a unit (of what). "5" means nothing on its own — but "5 metres" tells you a real length.
By the end you will be able to:
- explain what a physical quantity is and why a unit is always needed,
- name the SI base units for length, mass and time,
- use the prefixes kilo-, centi- and milli- to change units,
- choose the right measuring instrument for a quantity,
- find the scale division value of an instrument and read it correctly,
- write a measurement together with its accuracy.