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Electroboom: How Right IS Veritasium?! Don't Electrons Push Each Other??
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cbutlera:

--- Quote from: Nominal Animal on July 16, 2022, 09:49:38 pm ---
--- Quote from: imo on July 16, 2022, 09:39:22 pm ---We have got something like Planck scale, time, force, length, energy, temperature, volume, area, density, frequency, momentum, acceleration.. Why we cannot define the smallest blobs of energy then?
--- End quote ---
I do believe Feynman was making the same point as Magritte, when he painted "This is not a pipe".

--- End quote ---

I don't see Feynman playing with words in that way.  I think he meant exactly what he said.

We can quantify energy down to the smallest scales and make calculations with it without knowing what it is.  "Shut up and calculate" as the saying goes.  But what is a Joule?  I may see one Joule apparently moving from A to B.  Someone looking at the same event from a different reference frame may see five Joules apparently moving from B to A.  So what is this thing that moved?

With the battery, the switch and the light bulb.  If we know how the electrons move and how the electromagnetic field evolves, then there is nothing relevant missing from the picture.  We don't need to account for how the energy made the journey from battery to bulb.  We just know that if we have got our sums right then the total energy of the system will be conserved.
electrodacus:

--- Quote from: Naej on July 16, 2022, 11:32:32 pm ---What are all the forces on the vehicle?
Did you read Newton's second law?

--- End quote ---

Are you distracted by me using power instead of force ?
You can convert power to force at any time but power makes way more sense in this particular case with the available data and the questions asked.


--- Quote from: Naej on July 16, 2022, 11:32:32 pm ---The kinetic energy is 1/2*m*v². For this to be negative, the car would have to go not in a "different direction" but in an imaginary one.
In the real world, kinetic energy is positive.

Maybe do this easy exercise. A man is on a car travelling at 10 m/s (total mass=1000kg, no friction no engine). He pushes on a 1kg ball forward during 1s with 5N.
What's the speed of everything after, and what are the kinetic energies? And the powers?

--- End quote ---

All you need to have in that kinetic energy equation is a negative speed meaning speed in opposite direction.
There is already an easy exercise with 3 setups A), B) and C)
As I mentioned if you do not agree with that please solve it the way you think is correct.  Try not to invent more equation as you did on the wind power.

No friction and no engine suggest a vehicle coasting.
The ball is a bit strangely defined as mass is irrelevant if you provide the 5N constant braking force for a second that acts on the vehicle.

Vehicle starts at 0.5 * 1000kg * 102 = 50000Ws
After 0.1 seconds vehicle speed will drop to 50000Ws - (5N * 10m/s * 0.1s) =  49995Ws
sqrt(49995/(1000*0.5)) = 9.99949m/s
next 0.1 second   49995Ws - (5N * 9.99949m/s * 0.1s) =  49990.00026Ws
sqrt(49990.00026/(1000*0.5)) = 9.99899m/s
...
you get the idea 8 more time until you get to one second in 10 steps.  For more accuracy you can use 100 or 1000 steps
If you defined the ball as having a constant power say 50W instead of constant force of 5N calculation will have been much simpler.

And I guess the important part is that vehicle will have lower kinetic energy and lower speed than it did before the interaction with that ball.
electrodacus:

--- Quote from: cbutlera on July 16, 2022, 11:57:34 pm ---I don't see Feynman playing with words in that way.  I think he meant exactly what he said.

We can quantify energy down to the smallest scales and make calculations with it without knowing what it is.  "Shut up and calculate" as the saying goes.  But what is a Joule?  I may see one Joule apparently moving from A to B.  Someone looking at the same event from a different reference frame may see five Joules apparently moving from B to A.  So what is this thing that moved?

With the battery, the switch and the light bulb.  If we know how the electrons move and how the electromagnetic field evolves, then there is nothing relevant missing from the picture.  We don't need to account for how the energy made the journey from battery to bulb.  We just know that if we have got our sums right then the total energy of the system will be conserved.

--- End quote ---

The one joule was converted to something else while moving from A to B
In this case 1J of electrical energy was converted in to we may call thermal energy (the radiated photons).
Now you have 1J less stored electrical energy in the battery or charged capacitor and you have increased the temperature of the conductor due to electrons traveling through wire and interacting with the atom lattice of the material.
So immediately after you have thermal stored energy in the conductor due to conductor thermal mass that will slowly be radiated to space around as infrared (maybe even visible) photons so electromagnetic radiation.
Nominal Animal:
(Thanks, everybody, for not ridiculing my effort.)


--- Quote from: imo on July 16, 2022, 09:39:22 pm ---@Nominal Animal: the issue I see is the e-field in a good conductor is almost zero
--- End quote ---
So?

Do not forget that in a conductor, both the outermost electrons bound to atoms and free electrons "shared by the lattice" are in constant interaction with each other.  Although individual electrons' velocities are low, a perturbation in one spreads at about two thirds the speed of light in vacuum, exactly because they are interacting, and that interaction always occurs at c.  Again, the electrons are not particle-like here, they are well delocalized ("spread out"), and can be considered to "overlap".

A crude analogy would be marbles in a channel all touching each other, like a Newton's Cradle toy at rest.  Whenever you push one in at one end, one will pop out.  If you have many of them in parallel too, then the velocity of each individual marble is low, but the number of marbles pushed in and out huge.  If you knock one marble in, it takes only a tiny fraction of a second for the outermost marble to ping correspondingly, even though the velocity of any individual marble is very low.  (Consider, in particular, how the length of the marble chain doesn't really affect much how long that takes.)

If the electrons were to move like a rigid body, then the speed of electricity in a conductor would be infinite.  In practice, there is a bit of, uh, "flex?", in how the fields interact, so in typical conductors it is about two thirds of light speed in vacuum.  (It obviously depends on the lattice structure and the exact properties of the interacting electrons.)

If there is a significant electrical field in a conductor, the electrons would no longer have an uniform charge distribution (in the direction of that field).  Instead of a conductor, it would act more like a semiconductor or insulator.

It is exactly because the interactions spread out any perturbation so fast, that the electric field in a good conductor is minimal: the charge density (along the conductor, not necessarily across the conductor) stays nearly constant.


--- Quote from: cbutlera on July 16, 2022, 11:57:34 pm ---
--- Quote from: Nominal Animal on July 16, 2022, 09:49:38 pm ---
--- Quote from: imo on July 16, 2022, 09:39:22 pm ---We have got something like Planck scale, time, force, length, energy, temperature, volume, area, density, frequency, momentum, acceleration.. Why we cannot define the smallest blobs of energy then?
--- End quote ---
I do believe Feynman was making the same point as Magritte, when he painted "This is not a pipe".

--- End quote ---
I don't see Feynman playing with words in that way.

--- End quote ---
It is not wordplay.  It is a fundamental idea of what physics and mathematics are.  Philosophy, not wordplay.


--- Quote from: cbutlera on July 16, 2022, 11:57:34 pm ---I may see one Joule apparently moving from A to B.  Someone looking at the same event from a different reference frame may see five Joules apparently moving from B to A.  So what is this thing that moved?
--- End quote ---
Right.  Physics models the observations, and never tries to explain what 'that thing that moved' is; only quantify it and describe how it behaves.
Naej:

--- Quote from: electrodacus on July 17, 2022, 12:17:51 am ---
--- Quote from: Naej on July 16, 2022, 11:32:32 pm ---What are all the forces on the vehicle?
Did you read Newton's second law?

--- End quote ---
Are you distracted by me using power instead of force ?
You can convert power to force at any time but power makes way more sense in this particular case with the available data and the questions asked.

--- End quote ---
Did you read Newton's second law?
I think you distract yourself when there are 2 speeds involved.

--- Quote from: electrodacus on July 17, 2022, 12:17:51 am ---
--- Quote from: Naej on July 16, 2022, 11:32:32 pm ---The kinetic energy is 1/2*m*v². For this to be negative, the car would have to go not in a "different direction" but in an imaginary one.
In the real world, kinetic energy is positive.

Maybe do this easy exercise. A man is on a car travelling at 10 m/s (total mass=1000kg, no friction no engine). He pushes on a 1kg ball forward during 1s with 5N.
What's the speed of everything after, and what are the kinetic energies? And the powers?

--- End quote ---

All you need to have in that kinetic energy equation is a negative speed meaning speed in opposite direction.
There is already an easy exercise with 3 setups A), B) and C)
As I mentioned if you do not agree with that please solve it the way you think is correct.  Try not to invent more equation as you did on the wind power.

No friction and no engine suggest a vehicle coasting.
The ball is a bit strangely defined as mass is irrelevant if you provide the 5N constant braking force for a second that acts on the vehicle.

Vehicle starts at 0.5 * 1000kg * 102 = 50000Ws
After 0.1 seconds vehicle speed will drop to 50000Ws - (5N * 10m/s * 0.1s) =  49995Ws
sqrt(49995/(1000*0.5)) = 9.99949m/s
next 0.1 second   49995Ws - (5N * 9.99949m/s * 0.1s) =  49990.00026Ws
sqrt(49990.00026/(1000*0.5)) = 9.99899m/s
...
you get the idea 8 more time until you get to one second in 10 steps.  For more accuracy you can use 100 or 1000 steps
If you defined the ball as having a constant power say 50W instead of constant force of 5N calculation will have been much simpler.

And I guess the important part is that vehicle will have lower kinetic energy and lower speed than it did before the interaction with that ball.

--- End quote ---
The computation was simple, but ok.
How about this: one limo A at 10m/s its wheels are connected to a 1kW generator, another limo B is next to it at 11 m/s with a 1kW electric engine connected to the generator.
Which limo accelerates/decelerates?
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