Length Definition and 1000 Threads

I have tried to solve it and I would like a confirmation, correction or if something else is suggested... :) Helicoidal movement

I’m not a physicist but let’s say hypothetically ;we have the Millennium Falcon. It’s FTL hyperdrive can go Class 0.5 past lightspeed. Then we have an X-wing which has a Class 1 past lightspeed drive. This is all from the lore. MF is 0.5 and X Wing is 1 but MF is faster. Anyway even though the...

How to find the length of a wire of a 3000 Kelvin incandescent light bulb that produces L = 60W of power. The diameter of the wire is 0.00005m. I'm quite confused, as the resistivity of the bulb isn't given so I'm not sure what equation to use as resistivity = resistance × area / length does...

Hello, A light pulse moving bouncing between two mirrors (top and bottom) follows a vertical straight path w.r.t. to an inertial observer at rest relative to the mirrors. However, a moving inertial observer see the light pulse move in a zig-zag path as it bounced back and forth between the...

Hi PF! Fluids in low gravity have a natural oscillation frequency ##\lambda = \sqrt{\sigma / (\rho L^3)}##, where ##\sigma## is surface tension, ##\rho## density, ##L## characteristic length. Then given a particular object, say a sphere, is ##L=D## or ##L=r##? How about a channel; would ##L##...

Hola! So my first approach to this is use both the conservation of energy and momentum equations since collision between the first two objects are elastic. Let the 3 blocks be a,b and c (from left to right) Does this means the following: whereby ##v_{a} ##= speed of block a after collision...

A new (short 3 pg) paper, making quite a grandiose claim, caught my eye last night: https://arxiv.org/abs/1908.07719 Abstract: We propose an experiment of two-path interference in which the optical path difference between the two interferometer arms is much larger than the spatial spread of...

Hi All, Recently, I have been struggling to seek a solution for a seemingly simple flow question and try to rationalize my thoughts with mechanical engineering knowledge I have acquired from school but none of them can make me feel comfortable about answering the phenomenon I encountered in...

Homework Statement: A thin rod of length L and charge Q is uniformly charged, so it has a linear charge density ##\lambda =q/l## Find the electric field at point where is an arbitrarily positioned point. Homework Equations: ##dE=\frac{Kdq}{r^2}## A thin rod of length L and charge Q is...

The question is in the image. Working out with every step would be much appreciated.

Suppose we have a stationary metre stick with one end positioned at the origin of a stationary frame of reference, pointing along the positive x axis. The world lines of both ends of the metre stick are consequently vertical. Now consider another primed frame moving at velocity v relative to...

I figured out that the spring constant is inversely proportional to the natural length, but there’s still an unknown change in a quantity( most likely extension).

Summary: Hi, I'm doing an assessment for Physics on Optics topics, but I can't really explain how the CV affect the RV CV : Focal length of convex lens RV : Temperature of water after 20 minutes under the sun How I should explain for the temperature difference? 🤔 Please help, Thanks.

Can you transmit em wave with antenna much smaller than its wavelength? For example. ELF antenna is very long. Can you make one small enough to fit in the pocket by the device constructing the long wavelength part by part?

I am interested in purchasing Si, GaAs and/or Ge PN and PIN photodiodes, where the manufacturer would also supply the length scales as well as the doping, of the P, I and N layers. Commercial suppliers don't reveal this information [moderator: solicitation removed.]

I've managed to stump myself in attempting to answer a member on another forum. He is attempting to demonstrate length contraction using two electrons a known distance apart and moving at a known velocity.My thought experiment is based on his proposal; that's why I've chosen the components I...

What is the difference between time dilation (t is the stationary reference frame) t = Description: If two successive events occur at the same place in an inertial reference frame, the time interval 􏰋t0 between them, measured on a single clock And this equation for time, if we take t' as the...

##I_{total} = (I_{1} + A_{1}d_{1}^{2} ) + (I_{2} + A_{2}d_{2}^{2}) + (I_{3} + A_{3}d_{3}^{2})##(d is the distance between centroid of the individual box and centroid of whole shape.) By negative area method by joining the gaps in I section. ##I_{total} = (I_{1} + A_{1}d_{1}^{2} ) - (I_{2} +...

I'm trying to determine if a certain bicycle tire size will fit my bike, and that determination is based on the inflated diameter (or width) of the tire. As such, I'm trying to come up with a formula that will give me the diameter of a bicycle tire as a function of the tire's carcass width and...

Explained in statement.

So, I know it can be proven using calculus, but I need the geometric one. So, I got that ^c=^d and therefor, the amount of increment in one of a, is equal to the other(^e=^b). (Also 0<a+b<Pi/2) And AP'=BP'=BD/sin(a) and BP=BD/sin(a+b) and AP=BD/sin(a-b). AP'+BP'=2AP'=2BD/sin(a) and...

In order to try and sovle this problem, my idea here was to use an extremal argument, with two equal length maximum paths on a tree. I said that no matter where the two graphs started, they'd end up having to cross paths since if there were two distinct paths with equal lengths the graph would...

I have came across a term "coherence length of velocity field ##\lambda## ",tried to search in the internet but doesn't find any result...will anyone please give a brief summary of this in this context..

Two astronauts, Neil and Michael, visit a solid not revolving planet. They mount a jet engine on this planet to get it turning around its axis. Before starting the engine they put three dots on the surface with the help of an isosceles triangle, which measures 1 by 1 meter. Two dots are placed...

Is it known how much momentum a photon possesses if it's wavelength is at the Planck length, and what happens if it's momentum is somehow increased from that?

Richard Feynmann, in His lectures on Physics, Vol I, chapter 28. Gives an expression for calculating the E and B field of a moving point charge based on retarded radius; eg: Knowledge of where the charge was at the time when the field was being formed. The Equation was originally derived by...

L=Ra/P =6x0.0006/5x10^-8 =72000

I was always wondering if you can lift anything (no matter how heavy it is) if you just use a really long pipe. Or does torque increases in a way like ##e^x## , ##a^x## and after some point it barely increases? Also if this can be explained mathematically, I would love to see it.

If the table (with the mirrors, beamsplitter, etc.) is rotated 90 degrees, one arm will get shorter (due to lengthcontraction) because its longitudinal speed goes from zero to 30 km/s (our speed around the sun) and the other arm will get longer as its speed goes from 30 km/s to zero. So with a...

I have my PhD viva in about a months time, part of it is to give an introductory presentation. Since I'm sure some members here examine PhD students in their viva, I would like to ask what they would consider a good lenth of time for the presentation? I don't want to annoy the examiner by having...

Hello, The human eye has an average diameter of ##2.5 cm## and an optical power between ##60D## and ##64D##. An object can be brought as close as the near point which is about ##25 cm##. If ##d_{o}=0.25m## (object distance) and ##d_{i}= 0.025m## (distance to the retina), the optical power...

After watching a youtube video 2 years ago, the video said the smallest thing known is at Planck length, but could there be something smaller than Planck length

According to Sean Carroll's The Cosmological constant(https://arxiv.org/pdf/astro-ph/0004075.pdf) (Eqn.20) cosmological observations imply that the magnitude of the vacuum energy density in natural units is given by $$|\rho^{(obs)}_\Lambda|\le (10^{-12}\ \rm{GeV})^4.$$ Does this imply that the...

I got the first part of it down, $$L=\int_1^5 \sqrt{1+(\frac{1}{x^2})}dx$$ I just want to know if it's right to make your ##f(x)=\sqrt{1+\frac{1}{x^2}}## then compute it's second derivative and find it's max value, for the trapezoidal error formula.

What are the critical Reynolds number for fluid and characteristic length when a cylinder immerses and then rotates in the fluid (The fluid is initially static)? Please suggest the critical number for the transition from concentric flow to laminar and from laminar to turbulent flow. I would...

I tried -M=pq = f/(f-p) = f/f - f/p = 1-(f/p) => M+1= -f/p => -Mp-p=f But since it’s the y intercept, p will equal zero and so the focal length will be 0?

I tried following: $$ \Delta l = \alpha l_0 \Delta T $$ $$ (\Delta l)^2 l_0 = \alpha l_0^2 \Delta T \Delta l $$ $$ \Delta A l_0 = \alpha A_0 \Delta T $$ $$ \Delta A = \frac{ \alpha A_0 \Delta T }{ l_0 } $$ If we remember that: $$ \Delta l = \alpha l_0 \Delta T $$ So we have $$ \Delta A = \frac{...

I have computed the total length of a 3D triangle and its area. The code is shown below. I want to use file output instead of cout. The file name, cw2task1output, was just given as part of the task, in this case should I make an empty text file named cw2task1output then attach it to the resource...

First of all, Let me present some of the things I found from research. (considering convex lens) Interpretation 1 => Focal length is the distance from the center of the lens to the point where all rays converge. Interpretation2 => Focal length is the distance from the point of convergence to...

Homework Statement Use Desmos to graph the spiral ##r=\theta## on the interval ##0\leq\theta\leq4\pi##, and then determine the exact length of the curve and a four decimal approximation. Hint: ##\int \sec^3(x)dx=\frac{1}{2}\sec(x)tan(x)+\frac{1}{2}\ln\left|\sec(x)+\tan(x)\right|+C## Homework...

String theorists frame much of their studies in the context of Planck length. The theories are meant to fold together QM and general relativity. The equation for Planck length includes the gravitational constant, G. It seems to me the theorists are assuming the gravitational laws extend to...

So I just learned about projectile motion. I understand why you can study it as two independent straight line motions . But this can give you a way to calculate total velocities or accelerations, just by adding its individual component of each vector. If the initial position of the projectile...

Homework Statement a Basin contains water , a beaker is put upside down to a depth of 3m inside it , if the volume of the beaker is 250 cm^3 . and its C.S area = 200 cm2 calculate the length of the water column which rises inside the baker , supposed that their is no air leakage from the...

Ok this should be just an observation solution .. But isn't the equation for chord length $$2r\sin{\frac{\theta}{2}}= \textit{chord length}$$ Don't see any of the options Derived from that..

Homework Statement Serway Physics - P2.40 A glider of length 12.4 cm moves on an air track with constant acceleration (Fig P2.39). A time interval of 0.628 s elapses between the moment when its front end passes a fixed point A along the track and the moment when its back end passes this pont...

Homework Statement ##ABC## is a triangle, the midpoint of ##AB## is ##H##. Prove that ##2CH < AC+CB##. Homework EquationsThe Attempt at a Solution Note that by the triangle inequality that ##CH \le HA + AC## and that ##CH \le HB + BC##. Adding these two inequalities gives $$2CH \le HA+HB+AC+CB...

Can a single meter stick be one meter per A and less than a meter per B? If so, isn't this is a simple paradox? Does anyone here see it that way?

Homework Statement Let v, a, and b be the vectors (in the plane of the paper), all of which have length 1. (See attached picture). Let w be a vector of length 2 pointing directly out of the paper. Which of the following vectors is v×w? Homework Equations The formula for the cross product of...

I had posted a similar question on another forum but didn't get much of a discussion. I'm interested to know what people here think. So consider a spaceship midway between stars A and B and initially at rest in the reference frame of the stars. The ship then accelerates away from A to some...