2640 lumens. 1 foot.

2.3 kilograms. 9 volts. Aaah! I just closed the circuit with my tongue and

I felt all 9 of the volts. So what do all these things have in common? They’re units. Yes, but they’re also absolutely,

completely arbitrary. [Theme Music] You know who decides how much a kilogram weighs? A hunk of platinum and iridium known as the

International Prototype Kilogram or IPK. The IPK isn’t just how much a kilogram weighs.

In a very real sense the IPK is the kilogram. Every other kilogram is exactly the same as

the IPK, and the IPK is the lump of metal that decides

what that mass is. A kilogram is defined as being the same mass

as the IPK. We made kilograms up just like we made up

seconds and weeks and volts and newtons. There’s nothing about these things that makes

them them. Someone just decided one day that that was

a kilogram. Now the fact that I find units fascinating probably says more about me then it does about units, but I can talk about them all day. For example, did you know that the International

System of Units only includes seven base units and every other unit is derived from those

units? Speed is length divided by time. Acceleration is speed divided by time again,

so meters per second per second. Force is that acceleration multiplied by mass,

cause F=ma remember? Work done in joules is force multiplied by

distance. And power is work divided by time, so how much work can be done per unit of time. Makes sense. It goes pretty deep, and it’s absolutely correct to say that there are an infinite number of possible derived units, just most of them aren’t useful enough to

name. But here’s a bit of trivia for you. When I say watts or hertz, those things are just regular words. No special capitalization necessary. But Hertz and Watt, they were real people

with like last names that were capitalized. So what’s up with that? Well, getting a unit

named after you is kind of the holy grail of science. To quote Richard Hamming: “True greatness is when your name – like hertz

and watt – is spelled with a lowercase letter.” Of course when these geniuses were first piecing

together how the world works they had no idea that there were fundamental

basic units beneath it all. They were basing all of their units on arbitrary

values because, well, how could there possibly be a fundamental

amount of mass or distance. Interestingly, one of the standard base units is derived from an actual value though not a universal one. The second is 1/60th of 1/60th of 1/24th of the time it takes for the Earth to rotate a single time. That’s something, at least but it also illustrates

an interesting point. As fundamental as that seems, when you get down to the dirty details things start to get kind of cloudy. The Earth’s rotation for example is slowing

down. Does that mean that seconds should also slow

down? No. That would mess up every calculation ever. So seconds are slowly becoming less and less

based on reality. Now don’t worry. It’s gonna take forever for

the Earth to slow down noticeably. And when it does we’ll just keep adding leap

seconds to keep things balanced. But units are extremely important in chemistry

and in sciences in general, as we learned when the Mars Climate Orbiter

crashed into Mars because instructions were inputted in the

wrong units. Next time you get a B instead of an A because

you didn’t keep track of your units, just remember at least you didn’t destroy

a 300 million dollar mission to Mars. But what do I mean when I say keep track of

your units? Well. I mean watch them. Do not let them do anything you didn’t tell them to do because they’re sneaky. And a lot of chemistry is just converting

between units. So say you are in a car, and the car is going

60 miles per hour. Now right now everyone who doesn’t live in

America is like: “Boo, miles are terrible. Convert to kilometers

Hank!” Well I’ll do you one better. From a scientific

perspective, kilometers are terrible too. They’re just as arbitrary. We should use something

more universal. Like lightyears. The amount of distance light can travel in a year. And hours, hours is no fun. So let’s convert to lightyears per second.

60 miles per hour. When you say it it sounds like a whole number

with a single unit. But it’s not. It’s actually a fraction. 60

miles over 1 hour. Let’s start with the easy part. Getting to

the seconds. So first we’ve got to get to minutes. So there’s 60 minutes per hour. And also 1 hour per 60 minutes. That fraction once we have it can flip either

way. We want it with the hours on the top, on the

numerator. Why? Because we want the units to cancel. We want

to destroy the hours. We don’t want them in our units when we’re

done. And then the same thing happens again with

1 minute per 60 seconds. Now we go to lightyears. I asked Google, and there’s 1 light-year in

every 5.9 * 10^12 miles. Looking at this we see that the hours cancel

and the minutes cancel and the miles cancel. Leaving us with lightyears per second. That’s

really what matters. We’ve come out with the correct units. The rest is just hammering at the calculator

to discover that a car going 60 mph is also going 9.3 * 10^-12 lightyears per second. Now we perform an important test. The “does

this make sense?” test. And yes indeed it does because 9.3 * 10^-12

is a very, very, very, very small number. Which makes sense because when you’re traveling

in a car you’re going a very, very, very, very, very, very, very

tiny fraction of a light-year every second. Now there are probably gonna be fifty to a

hundred thousand people that watch this video. And I’m gonna guess that maybe a solid seven of you did the math along with me with your calculator out. Now I’m not giving you a hard time. That’s

just my guess. If you want to follow along with your calculator

in the future that might be helpful. It would at very least be very nerdy. But if you have been following along with your calculator, you might maybe have noticed something interesting. I said 9.3 * 10^-12. When your calculator… Your calculator probably said something like

9.3487658140029 * 10^-12. So why, when I had so many more numbers to give, did I only give two? Was I trying to save time? Well obviously not, because now I appear to

be wasting time talking about it. Do you think that it would be too hard for

me to remember all those numbers? Well obviously not, because I just did it.

So I will tell you why. When you’re doing experimental calculations, there’s two kinds of numbers. There’s exact and measured. Exact numbers are like the number of seconds

in a minute or the number of eggs in a dozen. They’re defined that way and thus we know them in effect all the way out to an infinite number of decimal places. If I say that there are a dozen eggs you

know that that’s 12. It’s not 12.0000000001 or 11.9999999. It’s 12. But that’s not true for the number of miles

per hour my car was going. That car wasn’t going 60.0000-out into infinity

mph. I only know the speed of my car to two decimal

places because that’s all I get from the speedometer. So the car could have been going 59.87390039 mph or 60.49321289 mph; the speedometer would still say 60. And no matter how well I measure the car’s

speed, I will never know it at the same level of precision that I know the number of eggs in a dozen. So that’s the second type of number, measured

numbers. Now the cool thing about measured numbers, because you never ever know them exactly,

is that they tell you two things at once. First, they tell you the number that was measured. And second, they tell you the precision at

which that number was measured. People often get their heads all tangled up

about this, but with a measured number you just have to remember that the actual number goes out to infinite decimal places, you just never know all of them. You can’t.

It’s impossible,. So when my scale says 175 lbs, that doesn’t mean 175.000000 lbs. It means 175.something lbs. And all those numbers after the five? We don’t

know them. And here’s the thing, a measured number can

be pretty unhelpful if you don’t have knowledge of the precision of the measurement. So you have to conserve the precision through

your calculations or else you might end up killing someone with

an imprecise dose of insulin or something. So we have a set of rules for what are called

significant figures: these are the digits in your number that you

actually know. With my speedometer there are two: 6 and 0. But 0 is weird, because sometimes it’s just

used as a placeholder. Like if I said that the fastest plane can

go 13,000 mph, which it can by the way. An unmanned military test glider did it in

2011. That’s not an exact number, those zeroes are

just placeholders. So when a number ends in a zero, or two or three zeroes, it’s hard to tell if those zeroes are significant. But this all gets so much simpler when you use scientific notation, which since it’s science we should. So 60 mph would instead be 6.0 * 10^1. We

get that zero is significant because we wrote it. Otherwise it would just be 6 * 10^1. We keep

that zero around because we actually know it. Scientific notation is awesome by the way,

once you get the hang of it. If you’re having trouble you can always just

type it into Google or your calculator to see exactly what number we’re talking about, but the number of the exponent just tells

you how many places to move the decimal point. So to the 1st power you move it one to the

right and you get 60. To the negative 1st power you move the decimal

point one place to the left and you get 0.60. To the fifth power, one, two, three, four, five, and you get six with five zeroes or 600,000. Of course your significant figures get preserved,

so 2.4590 * 10^-4 is 0.00024590 and you still get the same five sig figs. Now to the magic of figuring out how many

sig figs your answer should have. There are two simple rules for this. If it’s addition or subtraction it’s only the number of figures after the decimal point that matters. The number with the fewest figures after the

decimal point decides how many figures you can have after

the decimal in your answer. So 1,495.2+1.9903 you do the math. First you get 1,497.1903 and then you round

to the first decimal, because that first number only had one figure

after the decimal. So you get 1,497.2. And for multiplication just make sure the answer has the same sig figs as your least precise measurement. So 60 x 5.0839=305.034,

but we only know two sig figs, so everything after those

first two numbers is zeroes: 300. Of course then we’d have to point out to everyone that the second zero but not the third is significant, so we’d write it out with scientific notation:

3.0 * 10^2. Because science! Now I know it feels counterintuitive not to show all of the numbers that you have at your fingertips, but you’ve got to realize: all of those numbers beyond the number of sig figs you have? They’re lies. They’re big lying numbers. You don’t know

those numbers. And if you write them down people will assume

that you do know those numbers. And you will have lied to them. And do you know what we do with liars in chemistry? We kill them! Thank you for watching this episode of Crash

Course Chemistry. Today you learned some keys to understanding

the mathematics of chemistry, and you want to remember this episode in case

you get caught up later down the road: How to convert between units is a skill that

you’ll use even when you’re not doing chemistry. Scientific notation will always make you look

like you know what you’re talking about. Being able to chastise people for using the

wrong number of significant digits is basically math’s equivalent of being a grammar Nazi. So enjoy these new powers I have bestowed

upon you, and we’ll see you next time. Crash Course Chemistry was filmed, edited,

and directed by Nick Jenkins. This episode was written by me, Michael Aranda is our sound designer, and our graphics team is Thought Bubble. If you have any questions, comments or ideas

for us, we are always down in the comments. Thank you for watching Crash Course Chemistry.

Nice

Sig Dig"there are going to be 50-100.000 people watching this video"

Oh hank

2,554,070 viewsJust so no-one gets confused, we don't use IPK anymore, we use magnets, we stopped using IPK in late 2018 I think

HEY WAIT, THE UK USES MILES TOO…

I have to dumb it down for my science teacher

100-50k… this vid has 2.5mil views!

great informative content, but not everyone is a native speaker. Please go just a bit slower.

IPK is no longer the kilogram!

"50-100K viewers"

notices the 2.5 million viewsA second is actually 9192631770 periods of radiation that gets created by the transition of the two hyperfine levels of the ground condition of the atom cesium-133 (13th CGPM-1967, Rés 1)

We banned that arbitrary definition more than 50 years ago, apparently. Also, I don't fully comprehend what I just said yet. I just translated it from my BiNaS, a handy piece of literature we get to use on our exams here in the Netherlands. Stuff like the periodic table is in there and all. Also all formulas secondary schoolers (ages 16-19) are expected to be able to use.

I don’t know how he memorized 14 numbers

0 Celsius is the freezing point for water so that one is derived as well

helped me study for my test better than my teacher did.

50k-100k views you say.try 2000000+ views

Did anybody follow with their calculator

actually got 2 mil views hank

"There are probably gonna be 50- to 100-thousand people who watch this video…"

Six years later, the views count is at 2.57 million and

stillrising. 🙂Can someone give me clarity here. Using Hanks methods for Sig Figs for something like:

0.0002314

Decimal points of accuracy 7

SIG FIGS 4

2.314 x 10 to the power of 4

A small page l went on to brush up more on Sig figs say the scientific answer is 2.314 x 10 to the -4.

What did l miss? I thought moving the decimal to the right and it would be "power of". And to the left it becomes negative.

But this page l looked at, l got the answers in reverse. So when the point moves right its negative and to the left its standard power of…

What have a missed?

My answer: 0.0002314= 2.314×10 power of 4

Theirs: 0.0002314= 2.314×10 negative 4.

I like your science liars quote, but, wanna say that it’s not always true, since Pons, and Fleischman weren’t offed for their “discovery” of cold fusion.

50 to 100 thousand viewers… more like 2.8 Mil

Lol when he says 50k to 100k people watch this video when it's at 2.3 million

I only just started taking college level chemistry and thought my teacher was just being overly stern about representing significant figures. Now I realize he's actually trying to save my life.

You got me Hank, no calculator here lol

ugh 60 only has 1 sig fig

"BECAUSE SCIENCE" 10:09 lol

Sorry, love your videos, but there are a couple of errors here. At 6:45, you say that you only know your car's speed to 2 decimal places – that should be 2 sig figs. Also, at 7:01 you use the word 'precision' when it should be 'accuracy'. Actually, you use the term 'precision/precise' quite a lot when you really mean 'accuracy/accurate'. Accuracy is a term used to show how close a measured number is to a particular or accepted value, and is a measure of the performance of the measuring instrument; precision refers to how close a given number of measurements are to each other.

"There are probably going to be 50- to 100,000 people that watch this video…" 2.6 mill + views later

Wasn't hank sounding like umbridge at 10:28–10:30

Became so dark at the end

"You know what we do with liars?"

Me:we burn them in fire

Did anyone else notice he spelled metre wrong at 1:23?

IPK is now obsolete!! YAY!!

Now 1kg is not a platinum iridium

The end was a bit unsettling…

The kilo gram is actually no longer based off of the lump? It recently changed.

Love your videos!!! Greets from El Salvador.

Doesn't 305.034 round to 310

2019??

Wow..it started dark (literally), then ended dark (metaphorically.)

It seems to be a little over 50 000 views

There are probably going to be 50 to 100 thousand people who are gonna watch thisHow many Greens are there!?!?

At 10:29 I burned my chemistry book no.. JK

This video is great! But it needs an update. Quoth Wikipedia: "The kilogram, ampere, kelvin, and mole will then be defined by setting exact numerical values for the Planck constant (h), the elementary electric charge (e), the Boltzmann constant (k), and the Avogadro constant (NA), respectively. The metre and candela are already defined by physical constants, subject to correction to their present definitions." So after May of this year, no more silicon dioxide weights that keep changing mass for reasons we don't understand. What a relief!

Thanks for your attention and please keep up the good work!

10:09 BECAUSE SCIENCE!

Lol! Killing Liars with chemical bases muhahahaha

On 6:43 Hank tells 60.49321289 while the animation put a zero in between making it 60.493201289

0:07 this man just tried to taste a volt

WATT's up doc

Sometimes the truth HERTZ ???

Oh cmon, did you really just use word "pounds"/lbs in chemistry? Cmon, real chemist would never do that…

We know the exact speed of the car when it is at rest

whats a garmmar nazi?

I think this episode is the pinnacle of crash course humor

Your calculation is wrong in the light year per second

And you know what we do with liars in chemistry? We kill them!

…by dissolving them in Hydrochloric acid?

soon, this video definition of kilogram has to be edited lol

thank you for teaching me chemistry

I’m failing Chemistry and completely lost and it’s like every crash course assumes that you know something and is just revision. I don’t know where to start and have no previous knowledge. Any help?

All the dislikes are the people who use the imperial system

When you have an AP test in two days and and you are anxious out the bazooka and then you see Crash Course coming out of the clouds with angel music and then you bow and proceed to binge.

"Now there's probably gonna be fifty to a hundred thousand people who watch this video" Try 2.7 million.

"probably 50 to 100 thousand people will watch this video"

2.6M view count: am I a joke to you?

you're a GENIUS

Studying for an exam last minute be like, "Hank help me!"

50-100k…

I'm studying this to get into med school. and yes its better than college.

Dude this guy is hilarious. Such a great way to keep the audiences attention.

?

So at 10:08 — If I wrote down 30 x 10, would that also be correct scientific notation?

I think you need to update the definition of a kilogram…it has changed now and is no longer dependant on the physical "hunk of metal"…

5:19 wow that was like a 98% percent error.

"We might get 50-100,000 people watching this" – almost 2.7M views

This is a bit inappropriate but it’s hard to watch your videos because you’re very attractive. Big ups to your S.O. ??♀️ In all seriousness though, loved the info! ?

this would have gotten me into so much trouble in school with my teachers lol, im going to show this to my son to mess with his math teacher.

jokes on you I haven't owned a calculator since before this video came out

(but I do have access to google, which has free calculators galore….and didn't use it)

Crash course has literally everything that I need! Thank you!

sees titlehas horrific honors chem flashbacksMaybe is my brain fault, but I can not calculate9.3*10^-12 at 5:02. I only got 2.82*10^-15

50 to 100 thousand people who will watch this video… 2.7 million views later.

You are the BEST VIDEO HOST EVERRRRR!!!! Love you Bhaiya.

5:00 My calculator says 2.824858757E-15

uhh… help?

my i phone calculator kept sayin 0.00000000003 or something and i was stressed cuz i wasn't getting the answer in the vid or the answer in the comments and i sepent 30 whole minutes and i started thinking OH NO WONDER I FAILED PHYSICS. then i flipped my phone vertically and got 2.8 x 10^-15

You could update this video with the new definition of kilogram

Acceleration has a better equation.

Vf – Vi

A= ————

Delta time

Delta time is Tf – Ti

I have a question regarding this problem you worked out.: 60 x 5.0839 = 305.034. Wouldn't 60 only have 1 significant figure, since there is no decimal place following it. So, then the answer would be rounded to 300?

7:11 Oh really? I would have never noticed

Omgggg this made everything so much better!!!! Thank you I understand everything so much better.

I thought 60 was only 1 sigfig? not 2?

omg i think i love you lol

The addition (@9:40): (1495.2 + 1.9903) = 1497.1903, but becomes 1497.2 because of 1st decimal place precision. (One sig-fig?).

The multiplication ( 60 x 5.0839 ) = 305.034, but because of "two sig figs", becomes 300, then 3.0 X 10^2.

My question: Why did the first calculation ROUND to the required number of Sig figs, but the multiplication did not? (i.e. became 300, not 310.)

I'm I the only one does understand chemistry, I don't know why because i really understand your biology from the first time i watch it, I'm really getting pissed off

how do i even study this course

My chem teacher every day

10:28

6:53 – Hank, why don't u just look where u are going & stop staring at me like that with the creepy background sound ???

the 9.3 is wrong

10:05 i thought 60 has only 1 sig fig?? 🙁

Hank in 2013: "maybe 50-100k views"

2019: 2.7M views

Tells everyone not to run away from Chemistry in the first episode. And says, "do you know what we do with liars in Chemistry? We kill them" in the second episode. Well, THAT escalated quickly,,

The IPK doesn't define the Kilogram anymore

*Previous definition*: The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram.

*2019 definition*: The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.62607015×10−34 when expressed in the unit J⋅s, which is equal to kg⋅m2⋅s−1, where the metre and the second are defined in terms of c and ΔνCs.

Lmao I love this video