Welcome back. I will now introduce you to

the concept of momentum. And the letter for momentum is,

in physics, or at least in mechanics, it’s the letter P. P for momentum. And I assume that’s because the

letter M has already been used for mass, which

is I guess an even more fundamental idea. So P for momentum. So what is momentum? Well, you probably have

a general idea of it. If you see a big guy running

really fast, they’ll say, he has a lot of momentum. And if there’s a big guy running

really fast and a small guy running really fast,

most people would say, well, the big guy has more momentum. Maybe they don’t have a

quantitative sense of why they’re saying that, but

they just feel that that must be true. And if we look at the definition

of momentum, it’ll make sense. The definition of momentum is

equal to mass times velocity. So something with, say, a

medium mass and a huge velocity is going to have

a big momentum. Or something with maybe a medium

mass, but– the other way around. I forgot what I just said. So medium mass and big velocity,

huge momentum, or the other way around. Huge mass, medium velocity

would have maybe the same momentum, but it would still

have a big momentum. Or another way of doing momentum

is how little you would like to be in the way of

that object as it passes by. How unpleasant would it be

to be hit by that object? That’s a good way of thinking

about momentum. So momentum is mass

times velocity. So how does it relate

to everything we’ve been learning so far? So we know that force is equal

to mass times acceleration. And what’s acceleration? Well acceleration is just

change in velocity. So we also know that force is

equal to mass times change in velocity per unit

of time, right? Per change in time. T for time. So force is also equal

to– well, mass times change in velocity. Mass, let’s assume that

mass doesn’t change. So that could also be viewed

as the change in mass times velocity in the unit

amount of time. And this is a little tricky

here, I said, you know, the mass times the change in

velocity, that’s the same thing as the change in the

mass times the velocity, assuming the mass

doesn’t change. And here we have mass times

velocity, which is momentum. So force can also be

viewed as change in momentum per unit of time. And I’ll introduce

you to another concept called impulse. And impulse kind of means

that you think it means. An impulse is defined

as force times time. And I just want to introduce

this to you just in case you see it on the exam or whatever,

show you it’s not a difficult concept. So force times change in time,

or time, if you assume time starts at time 0. But force times change in time

is equal to impulse. I actually don’t know– I should

look up what letters they use for impulse. But another way of viewing

impulse is force times change in time. Well that’s the same thing as

change in momentum over change in time times change in time. Right? Because this is just the

same thing as force. And that’s just change

in momentum, so that’s impulse as well. And the unit of impulse

is the joule. And we’ll go more into

the joule when we do work in all of that. And if this confuses you, don’t

worry about it too much. The main thing about momentum is

that you realize it’s mass times velocity. And since force is change in

momentum per unit of time, if you don’t have any external

forces on a system or, on say, on a set of objects, their

combined, or their net momentum won’t change. And that comes from

Newton’s Laws. The only way you can get a

combined change in momentum is if you have some type of net

force acting on the system. So with that in mind,

let’s do some momentum problems. Whoops. Invert colors. OK. So let’s say we have a car. Say it’s a car. Let me do some more interesting

colors. A car with a magenta bottom. And it is, let’s see, what

does this problem say? It’s 1,000 kilograms. So

a little over a ton. And it’s moving at 9 meters

per second east. So its velocity is equal to 9 meters

per second east, or to the right in this example. And it strikes a stationary

2, 000 kilogram truck. So here’s my truck. Here’s my truck and this is

a 2,000 kilogram truck. And it’s stationary, so

the velocity is 0. And when the car hits the truck,

let’s just say that it somehow gets stuck in the truck

and they just both keep moving together. So they get stuck together. The question is, what is the

resulting speed of the combination truck and car

after the collision? Well, all we have to do is

think about what is the combined momentum before

the collision? Well let’s see. The momentum of the car is going

to be the mass times the car– mass of the car. Well the total momentum is going

to the mass of the car times the velocity of the car

plus the mass of the truck times the velocity

of the truck. And this is before they

hit each other. So what’s the mass of the car? That’s 1,000. What’s the velocity

of the car? It’s 9 meters per second. So as you can imagine, a unit of

momentum would be kilogram meters per second. So it’s 1,000 times 9 kilogram

meters per second, but I won’t write that right now just to

keep things simple, or so I save space. And then the mass of

the truck is 2,000. And what’s its velocity? Well, it’s 0. It’s stationary initially. So the initial momentum of the

system– this is 2,000 times 0– is 9,000 plus 0, which

equals 9,000 kilogram meters per second. That’s the momentum before

the car hits the back of the truck. Now what happens after the car

hits the back of the truck? So let’s go to that situation. So we have the truck. I’ll draw it a little

less neatly. And then you have the car and

it’s probably a little bit– well, I won’t go into whether

it’s banged up and whether it released heat and all of that. Let’s assume that there was

nothing– if this is a simple problem that we can do. So if we assume that,

there would be no change in momentum. Because we’re saying that

there’s no net forces acting on the system. And when I say system, I

mean the combination of the car and the truck. So what we’re saying is, is

this combination, this new vehicle called a car truck, its

momentum will have to be the same as the car and the

truck’s momentum when they were separate. So what do we know about

this car truck object? Well we know its new mass. The car truck object,

it will be the combined mass of the two. So it’s 1,000 kilograms plus

2,000 kilograms. So it’s 3,000 kilograms. And now we can use

that information to figure out its velocity. How? Well, its momentum– this

3,000 kilogram object’s momentum– has to be the same

as the momentum of the two objects before the collision. So it still has to be 9,000

kilogram meters per second. So once again, mass

times velocity. So mass is 3,000 times

the new velocity. So we could call that, I don’t

know, new velocity, v sub n. That will equal 9,000. Because momentum is conserved. That’s what you always

have to remember. Momentum doesn’t change unless

there’s a net force acting on the system. Because we saw a force is change

in momentum per time. So if you have no force

in it, you have no change in momentum. So let’s just solve. Divide both sides of this by

3,000 and you get the new velocity is 3 meters

per second. And that kind of makes sense. You have a relatively light

car moving at 9 meters per second and a stationary truck. Then it smacks the truck

and they move together. The combined object– and it’s

going to be to the east. And we’ll do more later, but we

assume that a positive velocity is east. If somehow we

ended up with a negative, it would have been west. But it

makes sense because we have a light object and a stationery,

heavy object. And when the light object hits

the stationery, heavy object, the combined objects still keeps

moving to the right, but it moves at a relatively

slower speed. So hopefully that gives you a

little bit of intuition for momentum, and that was not too

confusing of a problem. And in the next couple of

videos, I’ll do more momentum problems and then I’ll introduce

you to momentum problems in two dimensions. I will see you soon.

A cartruck now we have a new vehicle HAHAHAAH i laughed more than i should on this

Thanks for video ,Sir. It's good, but I didn't get you, when you said that;" if there is no force there is no change in momentum" .Ya, it's absolutely right .

But the one more thing you have done was you had used the same value of momentum as before (while truck was at rest), but if the car strikes the truck doesn't it giving a pushing force to the truck and even the momentum is same???

I hope you will reply it in a comprehensive way. Thanks!!!

Regards,

Christina 🙂

why is the quality stuck at 240p?

u r the best..ur all tutorials are so helpful. thankyou so much😙😙

Can't believe they're actually naming momentum as "p" and electric potential as "V". It's completely unrelated.

Why didn't they just named mass as a small 'm' and the momentum as capital 'M' ?

so force is the rate of change of momentum

Pretty useful, thanks!

Thanks this video was really helpful. Was this based on the conservation of momentum?

thanks for the video. very useful. What is the black board sofware?

Great video! It helped me a lot. Thank you very much.

Really helpful, this will definitely help me on my test tomorrow.

"CarTruck" LOL

What grade in the US is this concept taught? im curious. learning this for the first time in calculus based university physics.

I take physics as a Freshmen… is that weird ?

Can anyone tell me why he added 0 to 1,000kg times 9. Is it just a placement number or is he adding the velocity from the truck as well?!

@ 3:28, THe Unit of Impulse is "The Joule" ?? Is that what he said? Isn't it kgm/s or the N*s??

who runs this page…his name?

How did you get that new velocity of 3m/s?

Thank You 😊! It will help a lot in my exam tomorrow!

Thats Awesome i have a life that i dont understand this , thanks god , finally , Khan Academy thanks !

But then the equation E^2=(mc^2)^2 + (pc)^2 cannot explain light since it has no mass

I love your voice.

thank you very much

thankyou its really helpful you deserve a like👍

Letter for Impulse is "J"

… I assume that's because the letter "I" has already used for Moment of Inertia…

This video helped a lot and i have my physics final next Tuesday😭

goood

Can somoene explain when does momentum change in a system?

Lol, I've been watching these physics videos all day and got kind of bored, so I started messing around with the speed. Sal sounds so drunk when you set the video to .5x speed.

i also have a better concept in AP physics class.

is it just who prefer the old videos to new one? he just sounds sexier in the old vids XD

I got the problem solved in just 1 second without the math.

Waste of time

what is conservation of momentum?

i luv p.locopolous

https://youtu.be/vGeELTahWTA

It's important to note, I think, that this is an example of a COMPLETELY INELASTIC COLLISION, because after contact, the two objects begin moving together as a unit as though they were stuck together.

My new PHYSICS SOLVING APP.More then 150+ formulas,Solves for any variable you want,Covers up all physics.download now.https://play.google.com/store/apps/details?id=com.physics.lenovo.myapplication

thank you thank you thank you thank you

WHAT

http://physicsteacher.in/2017/11/18/momentum-impulse-theorem-newton/

love dis!!

As my highschool physics teacher for grade 11 always says, "biology isn't a science"

1:17 "how unpleasant would it be to be hit by that object" LMAO

A FOR AWESOME

impulse-J;momentum-p

Momemtum is Newton's first law like you already said before. Done, video ended.

Jk

Best physics lesson ever

great job sal. its impressive that how you conceptualize and explain it..

how about ball of pool that hits together and it hits the another and another how can the equation be is it m1v1 + m1v1 = m2v2 + m2v2

Measured in juuls

how to find mass and velocity using momentum???

proud to be bangladeshi cuzz da owner of da channel has bangladeshi roots

I hate these old videos… resolution is so low

Ok , so velocity = momentum/mass and mass = momentum/velocity and momentum = mass * velocity. hmm this reminds me too much of the loop distance , time , and speed seem to create because you can't have one without the other.

that's awsome

just curious, what year level are you learning this at school? or how old are you when you got taught this?

Thankgod there is no one to disturb on youtube like in class.

Can anyone explain conservation of momentum

thank you. cleared my doubt.

This was 10 years ago

Why we take delta as a change

And what is the proof that momentum Is more for a big guy

Give derivations of formulas from where it comes and why it holds

Why the momentum should be the same when car and truck hit like it was before hitting it please explain and there can be a change of force when they get hit by each other

Mass never change……

wait, will the new velocity be the square root of the initial velocity before momentum started, like for the car example?

If the internet had more of this and less off… that, we'd all be better off.

IMPULSE HAS NO UNITS

Nice 👍 thank you

The unit of the impulse can't be joules since joules is (kg*m^2)/s^2 and momentum is kg*m/s. Right? Impulse should be force X time, so (kg*m) since the seconds cancel out.

I was going to complain about the font but then I realised that it's a 10 years old video.

Taking this in my sophomore year of high school!!! This is so confusing…. 😩😩

"new vehicle called car-truck"

Allakh pandey sir( physics wallah) please also make a video on impulse and impulsive force.

HERESY!!!! joules is most certainly not the unit for impulse.

Am I supposed to be taking physics in 9th grade?

like the video but maybe you should have introduced a perfect inelastic and perfect elastic collision.

Thank you so much! Suppose the truck is moving against the direction of the vehicle, how will mathematical calculations of momentum,.

Sir which software are you using?

How can I download this video?

I want a car cartruck

I need a video where there is an actual explanation of the concept not just putting laws and etc

I feel like I’m in the future in 2019

Thanks for existing

1:18 Kinetic energy is a better representation of how unpleasant it is to be hit by an object. After a gun is fired, the gun and bullet have the same magnitude of momentum but the bullet has much greater kinetic energy.

thanks for helping, its 2019 by the way.

I love you again…. LIFE SAVER

how can u prove that f=ma

how can u prove that if we multiply mass and velocity of anv object then we will know how much force is required to stop that object

Does a bullet have a velocity or an acceleration and deceleration?

nice but mass have unit m not M

What makes change in time equal to unit in time?

But how does an impact on a 2000kg object not change the momentum?

P = mv

Unit of impulse is =J the equation is J=F•T unit Newton second (NS)

Units of impulse are NOT the Joule. Joule = units of ENERGY.

Units of impulse are the same as units of momentum because an impulse is just the change in momentum.

Units of momentum are the kg m / s ("kilogram meter per second")

3:28 joule? I thought it has the same units as momentum? Kg*m/s or N*s

Set playback speed to 0.5 he sounds like drunk then 🤦🏻♂️😂😂

wait so is this a inelastic collision?