Science Thread - General - Facepunch Forum

[QUOTE=MountainWatcher;30561549]Sup, so radiation happens naturally, right? And protons can turn into neutrons (ejecting a positron) which can turn into protons(emitting an electron), which means an up quark turns into a down quark after emitting a positron and a down quark turns into an up quark after emitting an electron. Soo, how does this not violate conservation of energy?[/QUOTE] Neutrinos. But this doesn't usually happen to protons by themselves since they are stable (at least more stable than a neutron). They only decay when subject to forces when they are in unstable nuclei. I'm not qualified to say anything about it though. [editline]19th June 2011[/editline] [QUOTE=PrusseluskenV2;30561557] Get out of that place when you can[/QUOTE] Working on it.

[QUOTE=MountainWatcher;30561549]Sup, so radiation happens naturally, right? And protons can turn into neutrons (ejecting a positron) which can turn into protons(emitting an electron), which means an up quark turns into a down quark after emitting a positron and a down quark turns into an up quark after emitting an electron. Soo, how does this not violate conservation of energy?[/QUOTE] I think it has something to do with the binding energy of the nucleus. Dunno though. [editline]19th June 2011[/editline] Free protons don't ever decay (or at least if they do, they have a half life longer than the age of the universe, and it's never been observed.)

Also, this half life thing, how does that work? Decay happens because of the weak nuclear force, right? Which only has atomic-level range. So how come other atoms influence how many atoms decay? Or am I looking at it the wrong way and it's just that there's a 0.5 chance of a certain atom decaying after a half-time?

[QUOTE=MountainWatcher;30562553]Also, this half life thing, how does that work? Decay happens because of the weak nuclear force, right? Which only has atomic-level range. So how come other atoms influence how many atoms decay? Or am I looking at it the wrong way and it's just that there's a 0.5 chance of a certain atom decaying after a half-time?[/QUOTE] It's all random. Just the amount decayed follows the exponential decay. Once again, nuclear physics :smith:, it's all atomic magic as far as i know.

Alright, then, electromagnetism, why do electrons flow from one end of a spire to the other when a magnet flies by? Also, what causes an electric current, electrons right? The actual current, what's measured in voltimeters and such.

[QUOTE=MountainWatcher;30562741]Alright, then, electromagnetism, why do electrons flow from one end of a spire to the other when a magnet flies by? Also, what causes an electric current, electrons right? The actual current, what's measured in voltimeters and such.[/QUOTE] The change in magnetic flux causes a force to be applied on the electrons in the metal spire, Causing a current inside the metal spire. (This in turn causes a magnetic field to be formed causing a force to applied on the flying magnet that is opposite the direction of the magnetic field, this is known as Lenz's Law) Yes, currents are the flow of electrons (or to be less precise, charge) in a circuit.Electric currents are cause by an E.M.F (or ElectroMotive force, which comes from the aforementioned flying magnet or a battery, where a chemical reaction provides an EMF) which can push the electrons around a circuit. The voltage is the amount of joules of energy per unit charge (coulombs). The actual flow of current is measured in Amperes (Amps) where the unit is defined as the flow of charge per second. Man why do I get all these Physics questions? (considering my physics exam is in 2 days time I'm beginning to think if this is an omen)

I get that it pushes the electrons ,what I DON'T get is why the move in the way they do. I'm assuming a spire isn't perfectly flat, so I would guess the electrons would try to be the furthest away from the magnet (or closest) as possible. Why is that position the opposite end of the spire? Also, another thing.The EMF force is the energy each electron gets, while U is the energy they lose that is transformed into something useful. Assuming there's no resistance in the circuit, we have that the energy lost in the generator is EMF - U, right? Energy at the start minus energy at point B. But U is the energy that each coulomb loses in the circuit. Meaning that, for Elost = EMF - U to be true, the energy/coulomb at the end of the circuit must be 0. Also, how come the speed of the electrons don't change? I mean, the reason they move is because there's a force from where they used to be and a force from where they are travelling to, the distance of the electron to each pole increases and decreases, depending on charges, the electron should speed up or speed down.

Refer to someone who actually has university level physics understanding of this. I can't explain that, sorry.

[QUOTE=MountainWatcher;30563986]Also, how come the speed of the electrons don't change? I mean, the reason they move is because there's a force from where they used to be and a force from where they are travelling to, the distance of the electron to each pole increases and decreases, depending on charges, the electron should speed up or speed down.[/QUOTE] Think of electrons in a circuit like a string of ball bearings in a metal pipe, so that no ball bearing can push past another one : they all have to stay in the same order. Now, when one electron (BB) gets pushed forward, all the others have to move as well. These little jostles spread out and so the whole thing has to move at the same speed. They can ALL move faster or ALL move slower, but you can't have some going faster and some slower. This might be an erroneous mental image, I'm not sure, but that's how I've always thought of it.

If one slows down, the repulsion forces from behind are bigger than the ones in the front, so he gains acceleration, repulsing the one behind him and exerting less force on the one in font of him, allowing the other to get repulsed by the one in the front. So they all have to be at the same distance to be in equilibrium, but are the effects in speed just not noticeable? And another thing, why the fuck does momentum, a random multiplication of mass and velocity matter more for predictions than the very essence of movement, kinetic energy? And we add directions to momentum but not energy. Why the hell not?

[QUOTE=MountainWatcher;30567615]If one slows down, the repulsion forces from behind are bigger than the ones in the front, so he gains acceleration, repulsing the one behind him and exerting less force on the one in font of him, allowing the other to get repulsed by the one in the front. So they all have to be at the same distance to be in equilibrium, but are the effects in speed just not noticeable?[/QUOTE] They're all pushing and jostling on a quantum level, but it averages out to a constant. [editline]19th June 2011[/editline] Energy is a scalar quantity - it has only magnitude. Momentum is a vector quantity - it has magnitude and direction. This is because momentum is a multiplication of a scalar (mass) and a vector (velocity). Kinetic energy is 1/2mv^2, that v^2 means multiplying a vector by a vector, which in this case gives a scalar (dot product).

[QUOTE=Turnips5;30568766]This is because momentum is a multiplication of a scalar (mass) and a vector (velocity). Kinetic energy is 1/2mv^2, that v^2 means multiplying a vector by a vector, which in this case gives a scalar (dot product - I MIGHT BE REALLY WRONG, don't take my word for that).[/QUOTE] Really wrong about what?

[QUOTE=JohnnyMo1;30568905]Really wrong about what?[/QUOTE] Multiplying a vector by a vector Because if you do the scalar product you get a scalar, and if you do the cross product you get a third perpendicular vector - only I haven't applied those things to physics yet (energy, in this case) so I'm just guessing. [editline]19th June 2011[/editline] covering my ass basically even though I think I'm right

No, yeah that's right. The dot product of two vectors is a scalar. But you can also say that you're just taking the magnitude of the velocity and squaring it. They're equivalent because of how the dot product works.

[QUOTE=JohnnyMo1;30568981]No, yeah that's right. The dot product of two vectors is a scalar. But you can also say that you're just taking the magnitude of the velocity and squaring it. They're equivalent because of how the dot product works.[/QUOTE] Oh yeah, of course. That actually makes sense.

[QUOTE=Turnips5;30568766]They're all pushing and jostling on a quantum level, but it averages out to a constant. [editline]19th June 2011[/editline] Energy is a scalar quantity - it has only magnitude. Momentum is a vector quantity - it has magnitude and direction. This is because momentum is a multiplication of a scalar (mass) and a vector (velocity). Kinetic energy is 1/2mv^2, that v^2 means multiplying a vector by a vector, which in this case gives a scalar (dot product).[/QUOTE] Then I say the same about velocity instead of momentum, why is velocity a vector? Energy has velocity as well, why not use the vector for velocity?

What. Energy doesn't have a velocity

[QUOTE=MountainWatcher;30569104]Then I say the same about velocity instead of momentum, why is velocity a vector? Energy has velocity as well, why not use the vector for velocity.[/QUOTE] Velocity is a vector... because we define it to be a vector. Or it's speed (another scalar) times a direction (really, you can't get much more vector than just a direction). [editline]19th June 2011[/editline] [QUOTE=JohnnyMo1;30569139]What. Energy doesn't have a velocity[/QUOTE] I think he means it has v in the equation. Maybe? Mountainwatcher, I explained in my last reply to you that v^2 will give you a scalar.

[QUOTE=MountainWatcher;30569104]Then I say the same about velocity instead of momentum, why is velocity a vector? Energy has velocity as well, why not use the vector for velocity?[/QUOTE] Velocity is a vector because it's the time derivative of a position which is impossible to represent accurately as just a scalar.

Kinetic energy is a quality that an object in motion has. It doesn't have any relation to which direction an object is moving. You can use the v to mean speed in that equation and it'll work just fine as well.

well it is the speed since that's what the magnitude of the velocity is

[QUOTE=JohnnyMo1;30569381]well it is the speed since that's what the magnitude of the velocity is[/QUOTE] Yeah. This whole thing is getting real redundant.

As momentum is. If you use speed, it's impossible to find negative momentum. And question, why DOES a product of two vectors produce a scalar?

Because of how the dot product works. It's corresponding vector components multiplied together and then all added up. You can also represent it as the dot product of vectors a and b is |a||b|cos(θ) where θ is the smallest angle between the two vectors. From that it's easy to see why it comes out as a scalar. There's no part of either of those two definitions that isn't just scalars and basic algebraic operations. [editline]19th June 2011[/editline] The second definition is also another easy way to see why a vector dotted with itself is its magnitude squared. The angle between a vector and itself is zero. Cosine of zero is one. One multiplied by the magnitude twice is just the magnitude squared.

But why is it right to multiply vector coordinates like we would do with scalar sums?

What do you mean "why is it right" [editline]19th June 2011[/editline] That's the operation a dot product performs on two vectors

Why don't we add a square in the middle, or a root or something. Why do we do it that way and not another? Like 2+2 = 4 and not 5.

[QUOTE=MountainWatcher;30570195]Why don't we add a square in the middle, or a root or something. Why do we do it that way and not another? Like 2+2 = 4 and not 5.[/QUOTE] Is this some kind of endurance test or what

[QUOTE=MountainWatcher;30570195]Why don't we add a square in the middle, or a root or something. Why do we do it that way and not another? Like 2+2 = 4 and not 5.[/QUOTE] That's not a sensible comparison. 2 + 2 = 5 is like saying vector v dot itself is |v|. We defined what operation + describes just as we invented the dot product, but in both cases the result you get is not arguable. It follows from the definition. [editline]19th June 2011[/editline] I don't understand what you don't understand.

What I'm saying is why the current dot product claimed superiority over all other dot products we could have invented. We know the definition of a limit is correct because it is in agreement with logic and previous mathematical premises. So, why do we multiply vectors as we do?