# Newton’s first law of motion | Forces and Newton’s laws of motion | Physics | Khan Academy

Human beings have always observed that if you have an object that is moving, so this is a moving object, traveling to the right here, that it seems to stop on its own. That if you do nothing to this moving object, on its own, this object is going to come to a stop. It is going to come to rest. And on the other side of things, if you want to keep an object moving, you have to keep applying a force to it. We’ve never in our everyday experience seen an object that just keeps moving on and on forever without anyone acting on it. It seems like something will always stop. And this is why, for most of human history, probably pre-history, but we definitely know the ancient Greeks all the way until the early 1600s, so for at least 2000 years, the assumption was “objects have a natural tendency to stop.” Objects … have … tendency … to come to rest or to stop. And if you want to keep them moving, you have to apply some type of a net force to it. And once again, this is completly consistent with everyday human experience, this is what we’ve all experienced our entire lives. But then these gentlemen show up in the 1600s, and you might be surprised to see three gentlemen here, because this is about Newton’s first law of motion. And, indeed, one of these gentlemen is Sir Isaac Newton. That’s Newton right over there [middle]. But these other two guys get at least as much credit for it because they actually described really what Newton’s first Law describes, and they did it before Newton. This is Galileo. And this is Rene Descartes. And they describe it in different ways, and Newton frankly gets the credit for it because he really encapsulates into a broader framework with his other Laws, and the Laws of Gravitation, which was really the basics of classical mechanics, and seem to describe, at least until the 20th Century, most of how reality actually worked. And their big insight, and it was very unintuitive at the time, {so now we come to the 1600s} Is that these three gentlemen said, maybe it works the other way. Maybe objects have a tendency to maintain their velocity, their speed and their direction. And if their speed is zero, they’ll maintain that restfulness. Unless they’re acted upon by an unbalanced force. So the completly opposite way of thinking. For over 2000 years, objects tend to stop on their own, if you want to keep the movement, apply a force. These guys say, Objects have a tendency to maintain their motion forever and the only way that you’re going to stop them is if you act on it, or accelerate them, or change their velocity, so either their speed or direction some way, is to act on them with an unbalanced force. But you might be saying, Hey, come on Sal, what’s going on? You just went through this, you said for most of most of human history, including my own personal history, this is what I observed [top right]. How can these guys say that this thing has a tendency to go on forever? This seems to break down. And their big insight was, well, maybe these things don’t have, by themselves, a tendency to stop, but because of interactions with their environment, forces are being generated that are acting against their motion. So when you think you’re leaving this thing alone, there is actualy a net force that is trying to stop it. And in this particular example over here, the net force is the force of friction. It’s the interaction between the block and the ground. So, when you think you’re leaving this thing alone, you actually have a net force going against its motion, which is the force of friction. And these guys realize that, because they said, look, if it was an innate property of the block, regardless of the environment, it should kind of always come to a stop in maybe a similar way. But they saw, if you made this surface a little bit smoother this thing would travel further and further. Maybe if you eliminated this friction, if you made this surface completely friction-less, completely smooth, this thing indeed would travel forever. And they didn’t have the luxury of launching satellites, and doing things in deep space, so it was a very, very unintuitive thought experiment. And you might say, what about this other thing, what happens when I am applying the force? Becuase in my everyday life, If I want to drag my TV set across the room I apply a force to it. And what these guys would tell you is all you were doing, if you were keeping the velocity of that TV constant, all you were doing was counteracting this net negative force. So if this was a TV dragging across your carpet, this is the force of friction acting against the motion of the object, and so you are essentially just balancing it when you push it. If you balance it perfectly, you will be able to maintain it’s velocity. If you want to accelerate it, you will have to apply even more force in the direction you are actually pushing it. Many thanks to Sal! π

## 46 thoughts on “Newton’s first law of motion | Forces and Newton’s laws of motion | Physics | Khan Academy”

first

• ### GameFrosts Post author

No one cares.

• ### iMovingTarget3 Post author

on my killing spree list

• ### theonewholistenstoinnercall Post author

Is it coincidence or what that he had uploaded similar kind of video exactly 13 months ago on the same date i.e. 13?

• ### Kram1032 Post author

I was immediatedely able to name Galileo and Newton from the pictures. And I guessed right on Descartes. Now I wonder why I thought it was him. It's always interesting to see that you know something implicitly but you have no idea how or from where…

• ### sharks42 Post author

i love Newtonian physics π

• ### Alvyn Walker Post author

Newtonian physics everyone should be familiar with it…. everyone.

• ### Ello M Skrilla Post author

I love leaning and watching these videos!!!

• ### Richard W Post author

ok, so are you going to turn to topics such as generators that have been made and silenced about the motion of current and electricty ?

Get a wig

• ### APhilosopher Post author

There should be a comment about how this law is "vacuously true", since there are in fact no objects in the universe to which no forces apply. I think this law is also analytically true now, isn't it?

She

• ### Jacob Brown Post author

When Galileo died, in the year after that he

Rebirthed

• ### asdf11221ify Post author

Excellent angle to approach this concept

• ### iibornfighter Post author

Finally youβre going back to science the think that actual matter in this world not stupid financial shit

• ### Zinghere Post author

isn't this a repost?

• ### tabu12000 Post author

ummm? how would newton have a tv?

• ### McMises Post author

i like the writing

• ### mobieus7 Post author

The point is the writing interfering with his speaking. He says something, then writes that down and says it while he is writing it, then reads it after he is done writing it while reading it very slowly. Most of us heard it well enough the first time.

muntain

get you!

• ### M. Jos Muscarelle Post author

Why do we continue to teach Newtonian mechanics , when it has been so elegantly replaced with Einstein's relativity?

• ### jesse10x Post author

i'm deaf. i like the writing.go back watching your porn.

• ### brenoakiy Post author

Einstein's relativity only applies to things that move close to the speed of light.

• ### M. Jos Muscarelle Post author

General relativity restates Newtonian gravity. The concepts of motion and things being "at rest" are also redefined in special relativity. It is not just about things moving close to the speed of light.

• ### rkrk7 Post author

give her the dick

• ### Lunazul Post author

but what of things? cells? molecules? atoms? houses? fabric? animals? what exactly?

• ### Kevin Rustles Post author

give her the d

• ### Zollo Beauty Post author

I disagree i PREFER him write it thank you for doing that btw!! Cuz i can reread everything at the end or if i didnt get it on the spot as he speaks i can pause to read and think. Thank You!!

• ### kachingaaa Post author

sexy* lol (?)

• ### Mr Pregnant - Atelston Fitzgerald Holder 1st Post author

I see a strong correlation between Hegelian's Dialectics; Thesis-Antithesis-Synthesis, and Newtons Laws of Motion. Antithesis is the contrast or opposition of an idea or concept, and synthesis is the unified whole of mutually exclusive elements, or the reconciliation of contradictory ideas where a new idea is formed, and this concept has been perfectly demonstrated within the medical context. Our perception of the world is constructed around polar opposites, a notion demonstrated in Issac Newton's Three Laws of Motion, a law in nature that laid the foundation for classical mechanics.

Primarily the "Third Law" which states; every force or action is contingent on an equal reactive force. Meaning if you push a cup on a table, it's motion and velocity should be perpetual, but what hinders or constricts is movement is an external force; like the friction on the table applied contrastingly to the cup in motion, hence it stops. Or the "First Law" which states; an object in uniform motion stays in motion unless acted upon by any given force.

• ### xoppa09 Post author

the idea that if you make the surface smoother (less and less friction) an object would go on forever, that is like a geometric idealization or platonic.

• ### Doge Post author

Small loan of a million dollars.

• ### Laid To Rest Post author

wut if it was going down a hill that went forever
would it stop then

• ### Supersoulstar Post author

By "maintain its velocity", does he mean keeping it at rest and then apply a harder unbalanced for to the right to actually make it move?

• ### Abd Alkader Abdeen Agha Post author

I know why it is different now, objects have become lazy so we need to apply force π

show

• ### Sumeya Hussein Post author

gsce physics 2017 anybody?

• ### Ronald Yacyk Post author

why does he repeat things 1000 times

• ### Jaimol John Post author

So is a book sitting on a table that isn't moving actually moving at a constant velocity but we just don't see it or realise it?

• ### Rubee Rajput Post author

First of al, tell us How an object obtains an initiall velocity, because an external force is also required to move an object

• ### Funny Rooster Post author

this video is very vague

• ### Trentamigthy0425 Post author

what does be use to draw/ write like this