Back

Four Fundamental Forces

⇐ Use this menu to view and help create subtitles for this video in many different languages. You'll probably want to hide YouTube's captions if using these subtitles.

Four Fundamental Forces : Gravity, Weak, Electromagnetic and Strong

相關課程

0 / 750

What i wanna do in this video
is give a very high level overview
of the 4 fundamental forces of the universe
And I'm gonna start with gravity.
and it might surprise some of you
that gravity is actually the weakest
of the 4 fundamental forces
And that is surpring cause thats what keeps us glued,
well not glued, but what keeps us from
jumping off the planet
its what keeps the moon in orbit around the earth
the earth in orbit around the sun
the sun in orbit around the center of milky way galaxy.
So it is a little bit surpring that it is actually the weakest
of the forces. and that starts to make sense when actually you
think about things in more of a human scale or a molecular scale
or even an atomic scale. Even on a human scale
your computer monitor and you have some gravitational
attraction, but you don't notice it or your cell phone and your
wallet, there is some gravitational attraction, but you don't see
them drawn to each other the way you might see 2 magnets
drawn to each other or repelled from each other.
and if you go even for a smaller scale you see that it matters
even less, we don even talk about gravity in chemistry, although
the gravity is there. but at those scales the other forces really start to dominate
So the gravity is our weakest.
If we move up a little bit from that, we get,
and this is maybe the hardest force for us to visualise, at least the hardest force for me,
is actually the weak force, sometimes called the weak interaction
and it's what's responsible for radiactive decay,
in particular beta minus and beta plus decay
and just to give you an example of a weak interaction
if I had some cesium 137
137 means that it has 137 nucleons
a nucleon is either a proton or a neutron
you add up the protons and neutrons of cesium, you get 137
and it is cesium because it has exactly 65 protons.
Now, the weak interaction is what's responsible for one of its neutrons,
essentially for one of its quarks flipping and turning into a proton
and I'm not going to detail of what a quark is, and all of that
and the math can get pretty hairy
but i want to give you an example of what a weak interaction does
so if one of these neutrons turns into a proton
we're going to have one extra proton
but we're going to have the same number of nucleons
instead of an extra neutron you have an extra proton here
and now it is a different atom it is now barium
and in that flipping, it will actually emit an electon
and, an anti-electron neutrino
I'm not going to go into the details of what anti-electron neutrino is
these are fundamental particles
but this is just what the weak interaction is
it's not something that is really obvoius to us
it's not just these traditional things pulling and pushing away from each other
like we associate with the other forces
Now, the next stronger force
and just to give you a sense of how weak gravity is
even relative to the weak interaction
the weak interaction is 10^25 times the strength of gravity
and you might be thinking:
if this is so strong, how come this does not operate on planets
or us relative to the earth
why doesn't this apply to intergalactical distances
the way gravity does
and the reason is
weak interaction really applies to very small distances
so it can be much stronger than gravity
but it only applies over subatomic scale
you go anything beyond that,
it kind of disappears as an actual force, or interaction
And now, the next force up the hierarchy,
wich is the one we are more familliar with
it is something that actually dominates most of the chemistry that we deal with
and the electromagnetism that we deal with
And that is, the electromagnetic force.
And just to give you a sense, this is 10^36 times the strength of gravity.
So it kind of puts the weak force in its place
it's 10^12 times stronger than the weak force
these are huge numbers that we are talking about
either this relative to that, or this relative to the gravity
so you might be saying, the electromagnetic force,
that is unbelievably strong, why doesn't that apply over
over these macro scales, like gravity
lemme write it down, macro scales
why doesn't it apply to macro scales?
and actually
there is norhing about the electromagnetic force why it can't
or it actually does apply overlarge distances.
The reality though, is that
you don't have such concentrations of either coulomb charges
or magnetism,
the way you do mass
so mass, since you have such huge concentrations,
it can operate over huge, huge distances
even though it's way way way weaker than the electromagnetic force
The electromagnetic force, what happens,
because it is attractive and repulsive,
it tends to sort itself out
sou you don't have these huge, huge concentrations of charge
Now, the other thing you might be wondering,
why is it called the electromagnetic force?
In our everyday life,
there's things like the coulomb force
or the electrostatic force, which we're familiar with:
positive charges, or like charges want to repel
if both of these were negative, the same thing would be happenning
and different charges like to attract
we've seen this before, this is the coulomb force,
or the electrostatic force
and then on the other side of the.. word i guess
you have the 'magnetic' part
and magnets, you know you've had played with magnets on you fridge,
if they're the same side of the magnet,
they're gonna repel each other
if they're the opposite sides, opposite poles,
they're gonna attract each other
who why is it called one force?
And it's called one force,
and once again, I'm not going to go into detail here,
it's called one force , because it turns out that
the coulomb force (electrostatic force) and magnetic force
are actually the same thing
viewed in different frame of reference
so I won't go into much detail,
but just keep that in the back of your mind
that they are connected
In the future video, I'm going (????)
of how they're connected (????)
It's more apparent when they're moving,
when the charges are moving in relativistic frames, and you have..
Just keep in mind that they are really the same force,
just viewed from different frames of reference
Now, the strongest of the forces,
it's probably the best named of them all,
and that's the strong force
and although, you've probably haven't seen this yet in chemistry classes
it actually applies very strongly in chemistry
because when you first learn about atoms, lemme draw a helium atom
A helium atoms ha two protons in his nucleus
and it has two neutrons,
and the it also has two electrons circulating around
So it has electron, and I can draw the electron much smaller
Well, I won't try to so anything in relative size,
but it has two electrons floating around.
And one question, that may or may not have jumped into your mind
when you first saw this model of an atom
is like: I see why electrons are attracted to the nucleus,
It has negative coulomb charge,
the nucleus has positive coulomb charge,
but what's not so obvious,
and what tends to sometimes not be explained in chemistry classes is:
These two positive charges are sitting right next to each other!
If the electromagnetic force was the only force in play
if the coulomb force was the only thing happening,
these guys would just run away form each other
they would repel each other
and so, the only reason that they're able to stick to each other
is that there's even stronger force
than the electromagnetic force
operating at these very, very small distances
so if you get two of these protons close enough together,
and the strong force applies only over very, very small distances
subatomic, or I should even say sub-nucleic distances
then the strong interaction comes into play
so then you have the strong interaction actually
keeping these charges together
And once again, just keep it in mind
relative to gravity, it is 10^38 times the strength gravity of
or it's about 100 times stronger than the electromagnetic force
So once again, the reason you don't see the strong force,
which is the strongest of all forces,
or the weak interaction,
applying over huge scales,
is that their strength dies off super, super fast
even when you start to go into large radius nuclei of atoms
the strength starts to die off, especially for the strong force.
The reason you don't see the electromagnetic force applying over large distances,
even though in theory it can, like gravity,
is that you don't see the type of charge concentration
the way you see mass concentrations in the universe
because the charge concentrations tend to sort themseleves out,
they tend to equalize
If I have a huge positive charge there and a huge negative charge there,
they will attract each other and then they become
essentially a big lump of neutral charge,
and once they're a big lump of neutral charge,
they won't interact with anything else.
Gravity, if you have one mass, and another mass, they attract each other
then you have a mass that's even better at attracting other masses
and so it'll keep attracting things to it.
So kind of snowball-like process
and that's why gravity can operate some of these
really, really large objects in our universe
and the universe as a whole

載入中...

Four Fundamental Forces

Four Fundamental Forces : Gravity, Weak, Electromagnetic and Strong