so quantities and units what do they mean well if we look at the letter C uh the letter C can represent many things in physics It could be for a material perhaps the specific heat capacity It could also be the speed of light or perhaps the capacitance It could also be the unit of electrical charge that we call the kum Now all of these are represented by the symbol C Uh and that's why you need to be aware in physics what is what Now in the two columns here the ones on the left are the amount of something And this is what we call a quantity A kulum is what we measure something in and that's a unit We can think about quantities in two ways It is the amount of something Now some things are fairly straightforward Some things are a bit more abstract But we can really think about things that just depend on the amount of something perhaps like the mass of an object or we can also think about things that depend on the direction like velocity or acceleration So we can really think about quantities in terms of scalar or vector quantities What you might see is that uh we only have 26 letters in the alphabet Uh and what we have to do then is think about a way of trying to represent everything that we have in physics So one way we can get around this is using uh either perhaps a capital letter or maybe a lower case and little c may be the speed of light Uh large C is capacitance Equally we might have the mass of an object or the moment And a little M and a big M mean very very different things But you soon realize we've only got 52 possible combinations and there are hundreds of things that we need So we use letters from other alphabets perhaps uh lambda or phi However this still doesn't quite solve our problem So what we can do is maybe combine them together Okay we have various combinations So the unit of pressure is a pascal pa However you have to know your stuff As you get more and more familiar with the course you'll see what units stand for what And context is important MC delta theta is going to be very different from E is equal to MC^ 2 Okay The context is absolutely vital