The Forces On You (Introducing Normal Force)

[Darrin1997]

What about atmospheric force?

[nafativedec]

In a more detailed way - The body and the ground are made of atoms, and the atoms have electrons which have negative charge. As we all now the same charge repel, so the electrons in the ground repel the electrons in your feet. It's due to the electromagnetic force that we don't fall trough the ground in the center of the earth.

[ClassicJustice]

Great videos; honestly, but who laughed at 2:06?

[naruto4ever66]

so is force normal just an application of newton's third law? when gravity pulls you down towards the earth, you are also exerting a force on the surface below you, and the surface reacts with an equal and opposite force on you?

[mrsg9064]

Greetings from San Diego, CA. Wanted to let you know that we are using your videos in my 8th grade science class. They are terrific!! The students really enjoy your style of "teaching". Thanks so much!

[DoomVik]

So... do you know why does atoms attract each-other and pushing away each-other?

[OfficialBrizzyBeats]

2:06 LOL c;

[T3AI2S]

2:06

lolololololololololololol

look at the picture

[MrLatrommi]

Good video. However, usually when we combine the normal reaction forces acting on a person's leg from the ground, we still draw this combined force's point of application from the ground and not from the centre of gravity of the person. You may also want to take note of the length of the vectors since they represent the magnitude of the forces.

[1veritasium]

@MrLatrommi Most introductory physics courses draw all forces acting through the centre of mass because this avoids complexities due to rotational motion.

[MrLatrommi]

@1veritasium Yes. It is quite obvious that the net moments about the c.g. of an object is zero if it is in equilibrium. Nonetheless, in this case, by drawing the combined reaction force from the ground acting on a person such that its line of action coincides with its weight, the principle of conservation of moments applies. A little cautiousness goes a long way, especially in education.

[matbonucci]

you're so cute, nice legs and feets

[MRH3LO]

@matbonucci u r a weird one mate

[AznS0ulja]

what is college equivalent to in terms of education, ive always thought its like uni? here in sydney, australia this is year 11 physics o.O uni physics would be far more advanced than this...

[bramshih]

You gave the example of standing on a spring or the ground, but what about standing on a weak wooden table? Eventually, the table would no longer be able to hold you up and would break. So my question is: are hardness and density (if those are even the right term) factors in the amount of normal force? If so, wouldn't this contradict with Newton's 3rd law because you can have "less normal force" than gravitational force?

[1veritasium]

@bramshih This is a good question. The answer is Newton's Third Law is never violated. If you are standing still the normal force must be equal to your weight. If a table breaks beneath you, then the normal force is less than weight and you accelerate to the Earth. This doesn't violate Newton's third law because the equal and opposite reaction force is actually the force with which you attract the earth. Check out my vid on Newton's third.

[bramshih]

@1veritasium Thanks for your response! I have actually seen many of your videos, including the one on Newton's third law. But that makes sense. Thanks for clearing that up!

[livedandletdie]

I knew it. Normal force is the kind off oppositee force to gravity sure gravity keeps you down but normal force keeps you not flat dead in the center of the core of the earth. I guess that it has something to do with why I'm not dead yet. But I like your explanation better.

[PBDPBD]

Another significant force is the pressure that is being applied by the atmosphere around you. Without it, the boiling point of the fluids in your body would be lower than your body temperature, thus making all the water in your body suddenly start to boil.

Personally, I think it's pretty important :P

[Enix2012]

Makes me think what would happen if everyone in the world jumped at the same time? O.o

[sidewaysfcs0718]

isnt the normal force really electromagnetism if we go all the way down to the basics?

the electrons in the surface of the ground are reppeling you , they are also responsible for the "spring-like" property of objects.

[MultiCheeseGrater]

@1veritasium Good job except assuming we are on earth for this question what about air pressure?

[TheAdamtheClown]

technically, the ground is moving....

*cough* tectonic plates *cough*

[jmoeller82]

very informative... at 2:06 the force of gravity gives your stick person genitalia

[fffanIX]

doesnt make sense.. theres no "force" truly pushing you back up. the only thing keeping you stationary is mass. which is not a force.. also, no one is ever stationary. we are constantly moving, falling actually. there is no upward force, because there is no true downward force. its just an attraction of mass.

[psypsy751]

@fffanIX mass x gravitational acceleration = weight (G force) and that is actualy pulling on you....and not down but again perpendiculary to the surface ...

[jharv300]

@fffanIX yes it does make sense, why do you think you have a weight force?? yes weight is a force caused by the acceleration due to gravity (9.81 ms-1) times your mass in kgs. if u drop something it accelerates downwards because it experiences a force. if there was no force it wouldn't accelerate - newtons 1st law. and if there is no force pushing you back up, whats stopping you falling into the earth??

[sidewaysfcs0718]

@fffanIX if there was no opposite force, then u would fall through the earth ....stationary is a relative term , relative to the ground , u are stationary.....i dont see how people can NOT understand this clip...

[H057IL3]

I love how the kid in back keeps disappearing.

[danielcarmi305]

There are also two more opposite forces acting on us:

1) The air around us presses on us constantly (air pressure)

2) The mass inside of us is also pressing outwards, preventing the previously mention force from imploding our bodies. :)

So technically speaking, our skin is being constantly crushed. And so is the membrane/skin of all our organs.

I find that pretty interesting.

[YairGeva7]

@danielcarmi305

Also:

1) each atom & molecule in our body's have opposite forces acting on each other or else we would have just burst into a cloud.

2) the moon and the sun are pulling us just like the earth is, just not in such a dramatic way.

[nubbs]

what about the force acting on the atoms in your feet and the ground that keep you from falling through the ground? 

[1veritasium]

@nubbs haha, yes that's important - that's what the analogy with the spring is meant to be. That reminds me of the story "turtles all the way down." Check it out on wikipedia.

[nubbs]

i think i meant more that the atoms in your feet are not actually touching the atoms in your flip flops, and those atoms are not actually touching atoms in the ground. and even though all those atoms are made up almost entirely of empty space, your atoms never fall through the earth's atoms. it's that force i was talking about. and technically the strong force is "on you" too. less newton, more QM. but hey, im only a philosophy student, and you've learned not to ask us questions. OIL THIGH!

[krishna830]

@nubbs Came here to post that as well. The Strong and Weak nuclear forces are always acting on any object which has atoms. These forces are required to ensure that matter stays intact.

[sidewaysfcs0718]

@krishna830 the strong and weak nuclear forces have no influence outside the atom's radius.

[tacticalstation]

Good job, you just clearly explained what most college physics professors attempt in 40 minutes to get across to their students.

[CakesnakeFilms]

@tacticalstation you learn about this in college? this is simple primary school (elementary school) stuff in england

[tacticalstation]

@CakesnakeFilms generally our primary school consist of a general understanding whereas in college we delve deeper into the mathematics of all things. not to say that the american educational system couldn't improve itself.

[CakesnakeFilms]

@tacticalstation fair point