Term 1 Week 5

This week, we have been learning physical quantities and units. If you have a certain amount of substance, or any other thing such as length, volume, time, how are you going to represent them? Furthermore, how are you going to ensure that the way you represent that particular amount of substance/time etc is the same universally? Thus we need units. Units are used firstly to tell the viewer what is being measured, then how much of it. Examples are cm, kg etc. These units are universal so that if one scientist in Singapore says that this substance is 100kg, a scientist in America knows exactly what him or her is talking about. In the past, we had different units across the globe thus sharing information was rather difficult. Furthermore the measurement system was much more complicated. The difference in magnitude between units was quite random, for example from one unit to the next would be *6, then *22 to the next, especially when measuring volume. This made conversion very difficult. Nowadays, out units are mostly if not all in increments of powers of 10 which makes conversion much easier since you only had to add or subtract zeros. Till this day, some measurements such as length are still slightly different across the globe, with the main two scales being cm and inches which are not related in increments of powers of 10.

Base quantities-mass (kg), length (m), time (s), current (A), temperature (K), amount of substance (mol), light intensity (cd) which stand for kilograms, metres, seconds, amperes, kelvin, moles and candelas respectively. These base quantities are all the quantities that are not derived, meaning that they are not a product or quotient of two other quantities. Examples of non base quantities are Newtons, speed, acceleration etc which are measured in kg/m/s^2, m/s and m/s^2 respectively. These are all SI units, the set of units recognised worldwide (note: not including inches) and are the main scale used when measuring objects.