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It is 32 degree now,
and it is pretty hot.
But 32 degree can actually be freezing
if we are talking about 32 degree
Ferenheit.
Difference in units makes a huge different!
The situation is bad indeed
when people from all around the world use different units in their daily life!
Let me give you an example,
in Malaysia,we use kg to measure (mass)weight.
But in other countries
for example, USA,
they use pounds.
For instance,
I am 70kg,
which makes me in normal weight(mass) for my height.
But if you tell your friend in America
”hey, that guy weighs 70”
They will exclaime and say
“70 pounds!? is he a hobbit?”
That is why,
in the late 18th century,
scientist from France saw the importance for everyone in the scientific field to use the same Unit of measurement,
and make everyone use meter for length
and kg for weight(mass).
This spark a movement that eventually leads to the development of, International System of Unit,
AKA, SI Units.
Here is the list of SI units.
Not using SI unit,
Yao Ming,
is standing 7 foot 6.
weighing 311 pounds.
But if you want to use Yao Ming as a physic test subject,
you need to use SI unit!
Hence when documenting Yao Ming as a test subject,
we need to use meter and kg
Yao Ming is 2.29meter tall and weighs 141 kg.
Its the same,
just different in units.
So what is the takeaway message?
Use the SI unit in all of your science writings.
and know some example of non-SI unit
should the teacher ask you to list them down in exams.
So, one day,
a base unit (meter),
is walking down the street,
and he saw another base unit (meter).
He told her,
I love you,
lets multiply,
and boom,
meter square is born.
So, derived quantity is
when one or more unit combines,
and becomes something different!
Meter measures length,
and when meter and meter combined,
it becomes the unit
meter square
that measure area.
and combine with yet another meter,
meter square becomes
- cubic meter
which now is a unit for, Volume.
Now this example is simple and already known by you,
but how about this:
Speed,
is how far you go,
in a second.
So, obviously,
meter divided by second,
you get speed.
Now, when I was a student,
I always analyse the base unit of the derived units that I am calculating,
to get an idea of how to calculate it.
For example,
if I have forgotten how to calculate speed,
I will look at the base units that makes up "speed"
ms-1
and read “meter divided by second”
and boom, there’s your answer.
Another example that I can think of is,
Newton,
the unit for measuring force,
has the unit of kg.ms-2.
If you look closely,
you will find that the ms-2 is actually the unit of acceleration.
Hence,
kg.ms-2 means mass(kg) multiply by acceleration(a).
I repeat,
Force=Mass x Acceleration.
There,
by looking closely at the base unit of Newtons,
you've learn about Newton's second law of motion,
which will be taught in chapter 2.
However,
if you want to breakdown Newtons into base units,
you will get,
kg, meters, and seconds.
Another derived quantity is density.
You may have learn from chemistry that density
means how heavy(kg) an object is,
per cubic meter (m3).
Hence, the unit of density is
kilogramme per cubic meter.
You know, just the other day,
I bought a sim card adapter,
which allows me to put a nano-sim card into a micro-sim adapter and then,
into a normal sim card adapter.
Young people nowadays really have it easy to remember all the scientific unit prefix.
There, you already know almost all of the unit prefix from your daily life!
Now let's try to remember about deca, hecta and pico, okay?
One of my favourite Professor once said,
"humans are all lazy, it is called conserving energy for survival".
So, scientist created special symbol or signs to represent the prefix,
so that they can write less letters.
And by special symbol or signs I mean the first letter of all the prefix,
except micro, which have a special sign, looks like an "U".
One thing to look out when writing these prefix symbol is,
some of them is in UPPERCASE,
like in case of Mega's M,
Giga's G
and Terra's T.
and others is in lowercase,
like kilo's k,
and %@$#.
look at the table.
It is quite particular!
Don't mess it up!
And, don't go crazy and draw all the Zeros when you are writing
super huge or super small numbers.
I am sure the only time that your teacher feels happy counting all the zeros,
is when someone handed them a check full of them.
Instead,
use scientific notation.
Count the number of zeros yourself,
and write it properly on the top right corner of the 10.
And when it is below decimal point,
count how many places it is below decimal point,
and write the number,
in negatives,
on the top right corner.
Just like what your math teacher taught you.
If nobody taught you,
you are smart,
just look at the table and figure it out yourself.