File "CE, Topic 1.1.1 - Ref from PaperPlainz on Vimeo.vtt"

Path: /PaperPlainz/Topic 1 Concept Explanations/CE, Topic 111 - Ref from PaperPlainz on Vimeovtt
File size: 5.51 KB
MIME-type: text/plain
Charset: utf-8

WEBVTT

00:00.000 --> 00:04.880
In this video we will talk about fundamental and derived SI units.

00:04.880 --> 00:11.800
We will see the reasons for using SI units, discuss the seven fundamental SI units, learn

00:11.800 --> 00:17.880
about derived SI units, and finish with an example about finding the fundamental SI unit

00:17.880 --> 00:20.720
combination of derived SI units.

00:20.720 --> 00:25.240
Let's see what SI units are and why most of the world uses them.

00:25.480 --> 00:31.480
SI is an abbreviation that comes from French and it stands for International System of

00:31.480 --> 00:32.480
Units.

00:32.480 --> 00:39.000
Before the French Revolution there were over 250,000 units used just in France.

00:39.000 --> 00:44.200
After the Revolution the Academy of Sciences created the metric system in order to unify

00:44.200 --> 00:46.440
and simplify the use of units.

00:46.440 --> 00:50.440
The International System of Units grew out of this attempt.

00:50.440 --> 00:56.240
So simply put, it allowed scientists to use a single system when communicating.

00:56.240 --> 00:59.040
There are seven fundamental SI units.

00:59.040 --> 01:04.920
These are the meter, the kilogram, the second, the ampere, the kelvin, the mole, and the

01:04.920 --> 01:05.920
candela.

01:05.920 --> 01:10.760
Only the first six are part of the IB physics syllabus.

01:10.760 --> 01:16.000
Outside these seven units, all other SI units are called derived SI units.

01:16.000 --> 01:20.880
This is simply because they are derived using one of the seven fundamental units.

01:20.880 --> 01:24.680
An example of a derived quantity is speed.

01:24.680 --> 01:29.240
Speed is equal to change in distance over change in time.

01:29.240 --> 01:34.280
Note that V stands for speed, S for distance, and T for time.

01:34.280 --> 01:39.680
The small triangle that you see in front of S and T is the Greek letter delta and means

01:39.680 --> 01:41.440
change.

01:41.440 --> 01:45.080
Distance is in meters, which is a fundamental SI unit.

01:45.160 --> 01:52.080
Time is in seconds, which is also a fundamental SI unit, so speed will be meters per second,

01:52.080 --> 01:57.400
which in physics we usually write as m, S to the power of negative one.

01:57.400 --> 02:03.040
You probably remember from math that the power of negative one basically means division,

02:03.040 --> 02:07.520
so S to the power of negative one means divided by S.

02:07.520 --> 02:12.800
This is why m, S to the power of negative one, stands for meters per second.

02:13.040 --> 02:18.680
Finally, let's see an example of finding the fundamental SI unit combination of derived

02:18.680 --> 02:20.440
SI units.

02:20.440 --> 02:25.680
We will find the unit of force expressed in fundamental SI units.

02:25.680 --> 02:29.480
Force is equal to mass times acceleration.

02:29.480 --> 02:35.240
Mass is a fundamental SI unit, however, acceleration is not.

02:35.240 --> 02:41.600
Acceleration is equal to change in speed over change in time, so we can write m times delta

02:41.600 --> 02:44.320
v over delta t.

02:44.320 --> 02:50.680
Time t is a fundamental SI quantity, however, v speed is not.

02:50.680 --> 02:56.800
Speed is equal to change in distance over change in time, so we can write m times and

02:56.800 --> 03:03.680
as you see here I have replaced delta v by delta S over delta t, so we get delta S over

03:03.680 --> 03:07.800
delta t divided by another delta t.

03:07.800 --> 03:17.440
After combining the delta t's in the denominator, we get m times delta S over delta t squared.

03:17.440 --> 03:25.360
S distance is a fundamental SI quantity, so now our equation only has fundamental SI quantities.

03:25.360 --> 03:29.000
All we have left is to write out the units of these quantities.

03:29.000 --> 03:36.240
M is mass and it is in kilograms, S is distance, it is in meters, and t is in seconds and since

03:36.240 --> 03:42.280
delta t is in the denominator and is to the power of 2, we get S to the power of negative

03:42.280 --> 03:43.520
2.

03:43.520 --> 03:49.560
So the fundamental SI unit combination of force is kilograms times meters times seconds to

03:49.560 --> 03:55.920
the power of negative 2, or in other words kilograms times meters per second squared.

03:55.920 --> 03:58.680
Let's summarize what we've covered in this video.

03:58.680 --> 04:02.800
We learned a bit about the history of the international system of units and that it

04:02.800 --> 04:07.280
allowed scientists to use a single system when communicating.

04:07.280 --> 04:15.240
We enlisted the seven fundamental SI units, meter, kilogram, second, ampere, kelvin, mole,

04:15.240 --> 04:16.240
and candela.

04:16.240 --> 04:22.880
A reminder that only the first six fundamental SI units are part of the IB physics syllabus.

04:22.880 --> 04:25.720
You will not work with the candela in this course.

04:25.720 --> 04:31.640
We discussed derived SI units, which are basically all other units outside the seven fundamental

04:31.640 --> 04:33.280
SI units.

04:33.280 --> 04:38.440
And finally, through our example, we have seen that derived SI units can be written

04:38.440 --> 04:41.760
as a combination of fundamental SI units.

04:41.760 --> 04:45.960
This wraps up our discussion of fundamental and derived SI units.

04:45.960 --> 04:50.480
In the next video, we will learn about scientific notation and metric multipliers.