Scientists
all over the world have agreed on a single measurement system called
Le
Système International d'Unités,
or SI.
This
system was adopted in 1960 by the General Conference on Weights and Measures,
which must contain a lot of bored
people.
There
are 7 SI base
units.
SI Base Units
| Quantity | Quantity Symbol | Unit name | Unit abbreviation |
| Length | l | meter | m |
| Mass | m | kilogram | kg |
| Time | t | second | s |
| Temperature | T | kelvin | K |
| Amount of substance | n | mole | mol |
| Electric current | I | ampere | A |
| Luminous intensity | Iv | candela | cd |
Derived SI Units
| Quantity | Quantity symbol | Unit | Unit abbreviation | Derivation |
| Area | A | square meter | m² | length x width |
| Volume | V | cubic meter | m³ | length x width x height |
| Density | D | kg per cubic mete | kg/m³ | mass/volume |
| Molar mass | M | kilograms per mole | kg/mol | mass/amt. of substance |
| Concentration | c | moles per liter | M | amt.of substance/volume |
| Molar volume | Vm | cubic meters per mole | m³/mol | volume/amt.of substance |
| Energy | E | joule | J | force x length |
SI Prefixes
| Prefix | Unit Abbreviation | Meaning |
| Tera | T | 1 000 000 000 000 |
| Giga | G | 1 000 000 000 |
| Mega | M | 1 000 000 |
| Kilo | k | 1000 |
| Hecto | h | 100 |
| Deka | da | 10 |
| base unit | - | 1 |
| Deci | d | 1/10 |
| Centi | c | 1/100 |
| Milli | m | 1/1000 |
| Micro | µ | 1/1 000 000 |
| Nano | n | 1/1 000 000 000 |
Well there were more but
all the 0's wouldn't fit, if you wanna know though, a pico is
1/1 000 000 000 000,
a femto is 1/1 000 000 000 000 000, and an atto is 1/1 000 000 000 000
000 000. You should take note that all of the prefixes
above the base unit are Greek, while all the ones under it are Latin.
Anyways to help us understand these quantities, here are some equalities.
A
kilometer is about 1/2 mile.
A
meter is about 1 yard.
A
centimeter is about as wide as a child's thumb. Not a big child though.
A
millimeter is about as thick as a small paper clip.
A
kilogram is a little over 2 pounds.
And for those of us who are more technical...
1
inch=2.54 centimeters
1
lb=454 grams
Ikg=2.2
lbs
1
liter=1.06 quarts
1
quart=0.96 liters
1
meter= 39.4 inches
We are about halfway through our session. If you would like to take a break or something, go ahead. I know what you're thinking though. You think if you leave now then you don't have to come back. Just think about all of the important things that you'll learn if you stay. We're going to talk about conversion factors!
Ok! Are we all prepared to LEARN? Alrighty then. You should know that the metric units are interrelated. For example...a cubic decimeter holds exactly 1 liter. Therefore, a cubic meter holds exactly one kiloliter, and a cubic centimeter holds exactly 1 milliliter. Also, a cubic decimeter of water weighs 1 kilogram. Therefore, a cubic centimeter of water weighs one gram, and a cubic meter of water weighs a metric ton. Woah! Ok, the hard part is over. Did you understand? I'm not sure if I did. Oh well, we need to move on.
Conversion Factors!
Conversion factors are convienient in so many ways. They help you convert from one unit to another. Suppose you are walking down the street and suddenly exclaim, "Oh my! How many grams are in 5 kilograms!" If you know about conversion factors you could figure it out in a jiffy. A conversion factor in technical terms is a ratio expressing the equality between 2 different units. Here is a model for converting metric measurements.
Model for Converting Metric Measurements
Steps:
1.
Problem: How many grams are in 5 kilograms?
Do not be afraid! I also have an explanation of that ever-so complicated model. But I know that you smart kids don't need that. But remember, the solution follows a pattern.
given x CF wanted units = find
CF given units
The fraction containing the conversion factor (CF) is set so that the given (old) units cancel, and that the found (new) units are in the numerator. I get it, so like in the problem up there the kilograms would cancel ot. That is like, so cool, cuz all you're left with is grams.
Lets practice. Say our problem is how many liters are in 250 milliliters.
Given:
250 ml
Find:
x in l
CF:1/1000
l = 1 ml
Solution:
250 ml x 1/1000 l = 0.25 l
1 ml
So, there must be 0.25 liters in 250 milliliters. If I did that right of course. Now I know there is an easier way to do this, the KHDudcm method. But that is for middle schoolers. I guess you could check your work with that though. So if we move the decimal point of 250 over to the left 3 places we do get 0.25. That is lovely.
If you are still here
I would like to congratulate you. This is all you will need to know for
the test tomorrow. But you're not taking the test are you! Such a pity.
I'm proud of you anyways. I would like to give you a gold star of excellence,
but I don't have one.
Well now that we are
all full of knowledge of metrics, we can all move to the country and eat
a lot of peaches.