In this video, I want to talk a

little bit about acceleration. And this is probably

an idea that you’re somewhat familiar

with, or at least you’ve heard the term

used here or there. Acceleration is just the

change in velocity over time. Probably one of the most typical

examples of acceleration, if you’re at all

interested in cars, is that many times

they will give you acceleration numbers, especially

for sport cars, actually all cars if you look

up in Consumer Reports, or wherever they give the

stats on different cars. They’ll tell you something like,

I don’t know, like a Porsche– and I’m going to make up

these numbers right over here. So let’s say that we

have a Porsche 911. They’ll say that a Porsche 911,

they’ll literally measure it with a stopwatch, can go

0 to 60 miles per hour. And these aren’t

the exact numbers, although I think it’s

probably pretty close. 0 to 60 miles per hour

in, let’s say, 3 seconds. So, although officially what

they’re giving you right here are speeds, because

they’re only giving you magnitude and no

direction, you can assume that it’s in

the same direction. I mean, We could

say, 0 miles per hour to the east to 60 miles per

hour to the east in 3 seconds. So what was the

acceleration here? So I just told you the

definition of acceleration. It’s change in

velocity over time. So the acceleration– and

once again acceleration is a vector quantity. You want to know not only

how much is velocity changing over time, you also care

about the direction. It also makes sense

because velocity itself is a vector quantity. It needs magnitude

and direction. So the acceleration

here– and we’re just going to assume

that we’re going to the right, 0 miles per

hour and 60 miles per hour to the right– so it’s going

to be change in velocity. So let me just write it

down with different notation just so you could

familiarize yourself if you see it in the

textbook this way. So change in velocity. This delta symbol right

here just means “change in.” Change in velocity over time. It’s really, as I’ve

mentioned in previous videos, it’s really time is

really a change in time. But we could just

write time here. This 3 seconds is

really change in time. It might have been, if you

looked at your second hand, it might have been 5 seconds

when it started, and then my 8 seconds when it stopped, so

it took a total of 3 seconds. So time is really a

change in seconds. But we’ll just go with time

right here, or just with a t. So what’s our

change in velocity? So our final velocity

is 60 miles per hour. And our original velocity

was 0 miles per hour. So it’s 60 minus

0 miles per hour. And then, what is our time? What is our time over here? Well, our time is, or we could

even say our change in time, our change in time is 3 seconds. So this gives us 20 miles

per hour, per second. Let me write this down. So this becomes,

this top part is 60. 60 divided by 3 is 20. So we get 20. But then the units are

little bit strange. We have miles. Instead of writing MPH, I’m

going to write miles per hour. That’s the same thing as MPH. And then we also, in the

denominator, right over here, have seconds. Which is a little bit strange. And as you’ll see, the

units for acceleration do seem a little bit strange. But if we think it

through, it actually might make a little

bit of sense. So miles per hour. And then we could either

put seconds like this, or we could write per second. And let’s just think

about what this is saying, and then we could get

it all into seconds, or we could all get into

hours, whatever we like. This is saying that every

second, this Porsche 911 can increase its velocity

by 20 miles per hour. So its acceleration is 20

miles per hour, per second. And actually, we should

include the direction, because we’re talking

about vector quantities. So this is to the east. So this is east, and then

this is east right over here– just so we make sure that

we’re dealing with vectors. You’re giving it a

direction, due east. So every second it can

increase in velocity by 20 miles per hour. So hopefully, with

the way I’m saying it, it makes a little bit of sense. 20 miles per hour, per second. That’s exactly what

this is talking about. Now we could also

write it like this. This is the same thing

as 20 miles per hour, because if you take

something and you divide by seconds, that’s the

same thing as multiplying it by 1 over seconds. So that’s miles

per hour-seconds. And although this

is correct, to me this makes a little

less intuitive sense. This one literally says it. Every second, it’s increasing in

velocity by 20 miles per hour. 20 miles per hour increase

in velocity per second. So that kind of

makes sense to me. Here it’s saying 20

miles per hour-seconds. So once again, it’s

not as intuitive. But we can make this so it’s

all in one unit of time, although you don’t

really have to. You can change this

so that you get rid of maybe the hours

in the denominator. And the best way to get rid

of an hour in the denominator, is by multiplying

it by something that has hours in the numerator. So hour and seconds. And here, the smaller

unit is the seconds. So it’s 3,600 seconds

for every 1 hour. Or 1 hour is equal

to 3,600 seconds. Or 1/3600 of an hour per second. All of those are legitimate

ways to interpret this thing in magenta

right over here. And then you multiply, do a

little dimensional analysis. Hour cancels with hour. And then will be

equal to 20/3600. 20/3600 miles per

seconds times seconds. Or we could say,

miles– let me write it this way– miles per

seconds times seconds. Or we could say,

miles per second– I want to do that in

another color– miles per second squared. And we can simplify

this a little bit. Divide the numerator

and denominator by 10. You get 2/360. Or you could get,

this is the same thing as, 1/180 miles

per second squared. And I’ll just

abbreviate it like that. And once again, this 1/180

of a mile, how much is that? You might want to

convert to feet. But the whole point

in here is, I just wanted to show you

that, well, one, how do you calculate acceleration? And give you a little bit

of a sense of what it means. And once again, this

right here, when you have seconds squared in

the bottom of your units, it doesn’t make a ton of sense. But we can rewrite

it like this up here. This is 1/180 miles per second. And then we divide by

seconds again, per second. Or maybe I can write

like this, per second, where this whole thing

is the numerator. So this makes a

little bit more sense from an acceleration

point of view. 1/180 miles per

second, per second. Every second, this

Porsche 911 is going to go 1/180 of a

mile per second faster. And actually, it’s

probably more intuitive to stick to the miles per

hour, because that’s something that we have a little

bit more sense on. And another way to visualize it. If you were to be

driving that Porsche, and you were to look at the

speedometer for that Porsche, and if the acceleration

was constant– it’s actually not going to

be completely constant– and if you look at

speedometer– let me draw it. So this would be 10,

20, 30, 40, 50, 60. This is probably not what

the speedometer for a Porsche looks like. This is probably more analogous

to a small four cylinder car’s speedometer. I suspect the Porsche’s

speedometer goes much beyond 60 miles per hour. But what you would

see for something accelerating this fast is,

right when you’re starting, the speedometer

would be right there. And that every second it would

be 20 miles per hour faster. So after a second

the speedometer would have moved this far. After another second

the speedometer would have moved this far. And then after another

second the speedometer would have moved that far. And the entire time

you would have kind of been pasted to the

back of your seat.

Why are people complaining about the units? It doesn't matter whether you call it mph, km or cowstitties ffs, how does it change the actual values?

acceleration is actually the rate at which the "speed"of a moving object changes in time.

not velocity!

That was best explanation ever. It's so use full to me. Thanks bro.🤗🤗

which software are u using to make videos

Why do you sound so mad?

Easy trick to go from km/h to m/s like 20km/h you just have to divide it by 3.6 to go to m/s 5,5m/s

Man Your The Reason Why I Almost Perfect my Exam In Science❤️

which car do you own sal?

here's a joke:

studying leades to success

success leades to happiness

happiness leades to slacking

slacking leades to sickness

sickness leades to death

so that's why don't study!

Thanks sir your videos did help and Im going to have a physics exam tommorow!Good luck to me

i'm having wars with physic…

IIRC, my Physics teacher told us to use a "+ or – " symbols when using vector units.

"Keep track of your Negative and Positive acceleration from your original coordinates"…

This makes the simplification easier at the end if you have multiple different or opposing forces at the same moment!

He was a former submarine commander IIRC. Seems he taught me well, all of this came rushing back!

Boy, do I miss and appreciate a good teacher now that I am trying to self-learn this math.

🙁

#RegretsNotLikingPhysics

#ShoutOutToMyChemistryTeacherMrsStrickland

Add more examples^^ Sometimes makes me confused

Best video Explaination. I think the dislikes are only for physics and not for Khan academy. Because this guy is a legend.

he butchered Porsche goddamit

bad

your voice is horrible

very nice explanation tysm for explaining😊😊😊now it's seems easy

very nice explanation tysm for explaining😊😊😊now it's seems easy

Adding more numerical to a single video would be nice

no use

I'm a bit confused how did you get 1 /180 please explain thank you

Wouldn't it be cool if a Porsche 911 s had a 0-60 of 3 seconds?

He's obviously smart and gets it and somewhat helped me but he talks too much and this video is too long. Also, he gets off topic.

It would've made more sense if he used M/S^2

Khan wat happens if the question doesnt provide the time but the only the acceleration and distance?

97 people don't like Porsches

You have helped me thanks

Khan academy saves my life cause my stupid science teacher doesnt make any sense litterally everyone hates her

Can you write it as 20mph/sec

Bro your handwriting is awesome! Especially in rush.

How can one calculate the speed during acceleration though?

Very nice

If yall are wondering, the SI unit of acceleration is m/s squared

My teacher discuss this to us but i didnt get to understand cuz my classmates so noisy and the other one is talking to me so i did get a chance to know very the accelaration and velocity

– Amber landingin

Very nicely explained!

This is the question I gotta do. An object of mass 30kg is in free fall in a vacuum where there is no air resistance. Determine the acceleration of the object. How do I do this

But what if the acceleration becomes faster over time? For example, it goes from zero to 20 in one second and then from 20 to maybe 60 in other second?

the entire time, you would've kinda been pasted to the back of your seat 9:02. :'D

Can I not just say 20 mph/s east?

Porsche did 911

HOW DO U FIND TIME WHEN DISPLACEMENT AND ACCELERATION ARE GIVEN

Hello bro what km/hr/ sec just change km/h to m/s and then its straightforward

thank you I couldn't get the information from my school either and I understood your explanation immediately thank you

Math is Evil, 9/11 😈

isn't the answer just 20m/s^2??

what if north to east

Isn't sec² = sec multiplied by sec??

So a = miles/sec multiplied by 1/sec.

And when we write

a = miles/sec/sec

The 2nd sec will go up to be like

a=miles/sec multiplied by sec

That'll be

a= (miles/sec) x sec??

Im confused is my maths procedure wrong?

Super

The video is 9:05 long and half of it is you showing us ways of writing the answer 😂 Let me tell you the problem isn't there, it's how to get the answer that most of us is here for.

почему нет субтитров на русском

it's nice to find a physicist who's also a car guy XD

shouldn't it be 0-60 in the equation and not 60-0 . since the car is moving from 0-60 and why not metres/second. who tf uses miles.

This didn’t help lol

Acceleration=change in velocity / change in time.. Simple formula

i love my physics class .___.

best teacher ever! could have a bit more animation but still awesome pls keep making more videos !!!! 🙂

PorscHE not porsh

“Porshe”, lol “Porsche”

I wanna ask a question, I did the conversion first, then calculate the acceleration and I got (72000 miles per hour square) I followed the way which my teacher told me, is it wrong ?? PLZ I need an answer be4 the med-term test 😢

5:42 bookmark

PORSCHE !!!!!!

First of all, ı am Turkish and ı did not understand this issue. thanks to the translation and thanks to you in a very nice way ı’ll follow you now and ı’ll learn again thanks you.(sorry the translation may be wrong)

Thank god there are people like this that care for kids learning.

Any idea about mprakash

I thought it's pronounced "por shei"

Talkative.

I hate physics.

You are a better teacher than mine

Very useful for my homework

Nice video… keep it up…

400th

I disagree with how the acceleration unit is reported. The change per meters, per change in seconds, becomes it's own unique derived SI unit. So then this creates two distinct units, with ⛺️m/⛺️s being one, and seconds ( time) being the other. Which then sets up ⛺️m/⛺️s = x , and time ( seconds) = y. Therefore x and y terms can't be collected so it's not seconds squared……

The Porsche 911 is exactly like a cheetah going from 0-60 in 3 seconds

"…if you take something and divide it by seconds, that's the same thing as multiplying it by 1 over seconds."

But where's the 1 at 5:10?

Edit:Oh shoot, I get it now!(16/4)/2=2

16/(4*2)=2

My son is studying for a test. This is very useful Sal.

For those of you who still don't get it:

20 mph/sec means that for every second the car is increasing it's speed by 20mph.ie,At the first second(t=1) it's speed is 20mph,the 2nd second(t=2) it's speed is 40mph(20+20),the 3rd second it's speed is 60mph(20+20+20) and so on-mph per second.

2019. teachers still suck 🙁

istg youtube teaches me better than all the teachers in school.

… or … 20 miles per second per hour. hmmm – let me think about that !

Are u mad ?u dont know hindi maddd

When he misspelled Porsche….

He sounds like Phil dunphy from modern family

"Porsche" just gonnaeave it out there

Has anyone use this for the mCAT?

you forgot to divide with 3 man

i learned this at school in 1 minute and this guy waste 9 minutes on something easy

Yeah this is unacceptable to my physics teacher

Thanks for the help 😭 My science teacher doesn’t make sense and I don’t understand anything until I searched how to solve acceleration. Your video saved me at the last minute because I’m literally up at 2 in the morning studying for a science quiz ;-;

This guys reminds me of Agent 14 from GTA V Online because of his voice.

I learned nothing from a 1hr class but this a 9min video helped me pass my test

Y’all have the answer to the packet

I like this

i find physics at the end very complicated…

This guy is a hero and public servant for good

i am feeling too much difficulty in EMT .I have to solve some questions but did"t find any solution.kindly help me.

what software do u use to explain and write?

Squared second?! What is the second? Move of Earth in equator of 460 meters (per second)? Or on poles close to zero meters? Or heart beat of passing life? Or relation between those two? What is the time? How time can be squared? Some basic terms has to be defined, starting from time.

thank you so much , شكرا جزيلا , danke so viel

2020 anyone?