In a 50 Hz ac voltage across a long wire, at a certain moment how does current vary along x, the wire length.

Were the retina at the back of our eye like a concave mirror then is it possible the image would be reflected back out the converging lens (under the iris)?

So the inverted image above is already formed in front of the retina (B’) and might essentially be re-inverted upright(B):

https://www.teachoo.com/10826/3118/Concave-Mirror---Ray-diagram/category/Concepts/

Then the image might be re-magnified on attempting to exit back out the converging lens under our pupil to potentially create a virtual image in the eye to simulate the reality we see:

https://www.teachoo.com/10838/3118/Convex-Lens---Ray-diagram/category/Concepts/#google_vignette

Cornea face reflection:

That way any appearance of eye beams from the eye would be passively reflected rather than actively emitted. However I don’t know the exact focal lengths of a potential retinal mirror to fully work out any resultant image.

An alternative theory might be to view the mind as being like a hidden periscope in the brain such that we’re desensitised to having an upside-down vision. Then the retina might function like a concave lens to minimise the image even further in order to reduce contrast with an upside-down version of the image:

“A researcher wearing goggles that inverted everything stumbled about wildly at first, but soon enough he was able to ride a bicycle.”

https://amp.theguardian.com/education/2012/nov/12/improbable-research-seeing-upside-down

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Hi all, this is my first post on the forum so please be nice.

I have been contemplating a device that is remarkably simple but, at least to me, somewhat curious.

We all know that if we bring two like magnetic poles together they will repel. Equally, if we insert a sheet of magnetically permeable material in the space between the repelling poles they will attract to the sheet.

Please examine the above drawing (sorry it is just a rough sketch).

On the left is a metal rotor that has slots cut in it so that it resembles a disc with metal fingers around the periphery. When rotated the fingers pass between the two opposing magnets that are fixed to levers. This will cause the levers to reciprocate as the fingers pass in and out of the space between the magnets. The other end of the levers have pins that run in grooves cut around a cylinder - you might consider it as a kind of double swash plate - causing the cylinder to rotate.

I imagine that there will be a cogging effect on the rotor caused by eddy currents in the rotor.

My question is, how does the inductive drag/eddy currents on the disc relate to the output power of the device?

]]>Hi, new here, though most interested in physics and its elementary subjects.

Have stayed around in physics sites at the internet since late 1990's.

~~~~~~~~~~~~~~~

And still the "universal" concept of "time" has never, to my knowledge, been satisfyingly explained in a physical and scientific manner.

This may be caused by:

1. Time is a most enigmatic function/ behavior/ dimension in science.

2. People have cognitive difficulties in general which the concept of "time" is revealing.

3. Science and physics is generally a "young" human discipline.

~~~~~~~~~~~~~~~~

To my layman understaning one have measured time historically by three main technologies.

1. Pendulum, hourglass, sun-orbits, and so on.

2. Chronographs, (clocks - electrical, mechanical, atomic, crystal).

3. Radioactive steady decay technology.

So, there are many ways in which time has been measured, still the origin of time is eluding our cognitive ability.

/chron44

]]>` because of Lavoisier quote('nothing is created and nothing is destroyed but everything is transformed')... `

Is it true?

If it's true it means that a tree removes heat from the environment as it grows,

therefore the difference in the quantity of trees (wood...) means that there is more solar heat in the environment compared to centuries ago and it can justify global warming regardless of the presence or absence of CO2...

Opinions?

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I have many "pellets" which are cone shaped. the rear is always 6mm in dia ,the front is 4.5mm.

This 4.5mm size varies slightly in manufacture.

it is very time consuming measuring with a digital caliper. i have seen a video on YT of a guy using a great method. the video is not great quality with no sound.

what he uses is a raised piece of wood to form a ramp. he puts a pellet at the top corner and lets go.

the pellet rolls in a arc. the pellets roll in different arcs depending on the size. he made little pots along the board edge to catch the pellet sizes.

What i do not understand is....... is there a calculation of the arc using the 2 dia sizes of the pellet

does the height of the slope effect the way any pellet rolls

hope that make sense,thank you

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When the ∂νL in (3.33) moves under the ∂μ in (3.34) and gets contracted, I'd expect it to become \(\delta^{\mu}_{\nu} \mathcal L\). Why is it rather gμνL ? Typo?

(In this text, gμν=ημν )

]]>Thanks

]]>Consider a shift of the field ϕ by a constant 4-vector ξ :

(1) ϕ(x)→ϕ(x+ξ)=ϕ(x)+ξν∂νϕ(x)+...

The infinitesimal transformation makes

(2) δϕδξν=∂νϕ

and

(3) δLδξν=∂νL

Using the E-L equations, the variation of Lagrangian is

(4) δL[ϕ,∂μϕ]∂ξν=∂μ(∂L∂(∂μϕ)δϕδξν)

Using (2) and (3),

(5) ∂νL=∂μ(∂L∂(∂μϕ)∂νϕ)

or equivalently

(6) ∂μ(∂L∂(∂μϕ)∂νϕ−gμνL)=0

The conclusion is, "The four symmetries have produced four Noether currents, one for each ν :

(7) Tμν=∂L∂(∂μϕ)∂νϕ−gμνL

all of which are conserved: ∂μTμν=0 ."

My question:

where in this derivation the assumption was used that the transformation is a symmetry?

P.S. I am sorry that LaTex is so buggy here. I don't have a willing power to do this again. Ignore. Bye.

]]>On the p.17 it says,

Shouldn't it say *force* rather than *potential*? Isn't any potential rather *quadratic* close to equilibrium?

F = ma= (G*M_{1}*M_{2})/R^{2}

1. F = ma

2. F = G M_{1}M_{2}/ R^{2}

Second- If it is right does G/R^{2} represent the acceleration part of F= ma ?

If we take entropy as being proportional to information then information is not constant as Entropy is not constant.

The Second Law of Thermodynamics states that the state of entropy of the entire universe, as an isolated system, will always increase over time.

If Entropy is increasing then information in universe is also increasing.

Let's say it is Quantum mechanics for which information is increasing. Quantum mechanics describes how the 12 fundamental particles behave. But it is a probabilistic theory. Because fundamentally it is random, new information is being created every time a quantum event occurs. In that case it could be these quantum measurement which are increasing the entropy of the universe as they are creating new information. The higher the entropy the higher the information if fundamentally quantum events are what is creating said information then entropy might be proportional to quantum events.

So the number of quantum event might be proportional to the number of entropy. Indicating that if there is a high entropy count then there will be more quantum events. Then the highest entropy spot might be where most of quantum events are taking place.

Stephen Hawking showed that black holes emit radiation known as Hawking radiation. By this hawking confirmed that black holes have entropy. He also determined how much entropy they have. The super massive black hole at the center of the Milky Way has about 10 to the 91 Boltzmann constants of entropy. That is 1000 times as much as the early observable universe, and 10 times more than all the other particles combined. And that is just one black hole. All black holes together account for 3 times 10 to the 104 Boltzmann constant of entropy. So almost all the entropy on the universe is tied up in black holes.

So, Hawking's radiation being very high entropy, should hold most quantum events of the universe.

]]>Undoubtedly, it is incredibly difficult to take into account all the factors even in a triangular or tetrider coordinate system, which is difficult even for visual perception. And in its direct form such a solution is impossible. But it is precisely this system that allows the logical formation of figures that we can see in water - a ring vortex or torus, similar to a figure eight (infinity) and a hexagon, similar to a snowflake or polar vortexes of gas giants.

Let's imagine a homogeneous medium that consists of individual particles. The only possible position of the particles relative to each other, at which absolute homogeneity is achieved, is a tetrider, or for simplicity, a triangular lattice in one plane, at the intersections of which the particles are located. Thus, all distances between particles are the same. Particles interact with each other by being attracted at a distance and repelled upon collision, which is caused by the forces of molecular attraction and repulsion.

Now suppose one particle received an impulse and moved from its place in the direction of the other two. If we considered particles as billiard balls, then we could assume that the momentum would be divided into two. But in this case we have forces of molecular attraction and repulsion, which allow us to regard further interaction as a chain reaction similar to the domino principle, where momentum is transmitted indefinitely due to the force of gravity. Having logically followed the trajectory of the particles, we will see that the impulse in a circle on both sides, forming a figure eight, returned to the first part, which caused the action, which will lead to an endless repetition of the process. It is precisely this mechanism that underlies the ring vortex, which under ideal conditions, according to viscous friction, can exist endlessly dissipating its energy.

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If we take entropy as being information then information is not constant as Entropy is not constant.

The Second Law of Thermodynamics states that the state of entropy of the entire universe, as an isolated system, will always increase over time.

If Entropy is increasing then information in universe is also increasing.

Let's say it is Quantum mechanics for which information is increasing. Quantum mechanics describes how the 12 fundamental particles behave. But It is a probabilistic theory. Because fundamentally it is random, new information is being created every time a quantum event occurs. In that case it could be these quantum measurement which are increasing the entropy of the universe as they are creating new information.

So the uncertainty of quantum particles might be proportional to the number of entropy .Indicating that if there is a high entropy count then there will be more quantum events.

Stephen Hawking showed that black holes emit radiation known as Hawking radiation. By this hawking confirmed that black holes have entropy. He also determined how much entropy they have. The super massive black hole at the center of the Milky Way has about 10 to the 91 Boltzmann constants of entropy. That is 1000 times as much as the early observable universe, and 10 times more than all the other particles combined. And that is just one black hole. All black holes together account for 3 times 10 to the 104 Boltzmann constant of entropy. So almost all the entropy on the universe is tied up in black holes.

So, Hawking's radiation being very high entropy, should hold most quantum events of the universe.

]]>Can you please help me figure out how this toy works? I realized that it is kind of wound up and it, accordingly, spins. But please help me to understand this question in more detail. Perhaps someone has some ideas? I would be very grateful. I would especially appreciate diagrams.

]]>Also, if this is in the wrong category, let me know. I'm not very used to forums.

]]>I would like to know if more than one wavefront can be used, to create a smoother or more complicated animation ?

]]>I have a situation that I need help with. There is a van on the street and someone took a photo of it.

I have uploaded 2 photos here

What I need to know is how far is the top of that white hinge from the ground (so the distance between the red line and the ground) and how far is the bottom of that white hinge from the ground (so the distance between the green line and the ground).

Some information that might be helpful:

This van has a California license plate. in California, license plates are 12 inches by 6 inches.

The van is a Ford Transit 150. I don't know what year.

I don't know how far the camera was from the van.

with the exception of the van, I can measure anything that appears on that street and report back.

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