Four fundamental forces Gravity, Weak, Electromagnetic and Strong
Four fundamental forces
- 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
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At 5:31, how is the moon large enough to block the sun? Isn't the sun way larger?
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When naming a variable, it is okay to use most letters, but some are reserved, like 'e', which represents the value 2.7831...
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This is great, I finally understand quadratic functions!
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At 2:33, Sal said "single bonds" but meant "covalent bonds."
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