SI Units

– [Lecturer] One of the
most important concepts to really grasp and
understand, as a scientist, is that numbers have absolutely no meaning until you give them context. And that context comes
in the form of a unit. So for example, if I tell
you that my weight is 100 that just doesn’t mean anything. But, if you say 100 pounds,
then, all of a sudden, you know how much I
weigh, I weigh 100 pounds. The unit here, the unit of pounds, gives this number, 100,
context, it gives it meaning. In your everyday life you
hear lots and lots of units, I mean dozens are units, right. Kilograms and grams, there’re
many, many, many units that you hear. And as a scientific community,
we’ve reached a point where we recognize that there
are so many different units that are being reported in
the scientific literature, that we needed to standardize
things, or normalize things. So we came up with a system
of units called the SI system. Okay, we call these our SI units. SI means system international, or the international system of units. And these are a collection of units that all other values are based on. And we have five really
important units that we, as a scientific community, we need to know because these are the
baseline of everything else. So these are gonna be distance, so we’re gonna have an
SI unit for distance, for time, for mass, for temperature, and, finally, for amount. Okay. So the SI unit for distance is the meter, and we give this the symbol lowercase m. The capitalization’s important here, this is a lowercase m. The SI unit for time is the second, and, again, this is the
lowercase, this time it’s s. Mass is the only SI
unit that has a prefix, the SI unit for mass is the kilogram, it’s not the gram, that’s
a very common mistake. So the kilogram has a
lowercase k, a lowercase g. Okay, that’s the kilogram. The SI unit for temperature
is not what you might think, you might think it’s degrees
Celsius or degrees Fahrenheit, but in fact, it’s what’s known
as the absolute temperature, which is Kelvin, and
this gets a capital K. I want you to note, this is not
degrees Kelvin, it’s Kelvin. So temperatures are reported
in Kelvin, not degrees Kelvin. And amount, this is gonna be one that becomes incredibly
important in this class, the SI unit for amount is the mole, which we abbreviate as
lowercase m-o-l, so a mol. So these are your SI units
that you really need to know. All other units are gonna be
based on these five units. In the next video, we’re
gonna see how these five units can be used to determine
SI units for other values, that don’t fit within these categories. For example, area, or volume, or speed.

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