# All Questions

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124 views

### How do we know that spacetime is uncountable/continuous/etc.?

Every major theory in physics - from classical dynamics, to quantum mechanics, to general relativity - makes assumptions about the structure of spacetime. Among the most common assumptions are that ...
26 views

### Correct relationship between the electric field and voltage at a distance from point charges

Hello I'm wondering if this is a correct understanding of the electric field and voltage strength as a function of distance. I'm helping a fellow student with their homework and I don't want to say ...
55 views

### What is the total cross section for $H \rightarrow W^{+} W^{-}$?

I need to know the total cross section for the process $H \rightarrow W^{+}W^{-}$, but cannot find it anywhere. Decay widths for Higgs decays are mentioned in Peskin and Schroeder (page 776), but I ...
69 views

### What is the most basic system that exhibits states of matter?

I'm trying to develop a more intuitive understanding of the states of matter..specifically the difference between solid and liquid. To this end, I'd like to consider the most basic system in which the ...
18 views

### What is the current in the circuit if the LED measures 2 volts? [closed]

Draw a series circuit with a 6v battery, an LED and a 330 ohm resistor. What is the current in the circuit if the LED measures 2 volts? I was able to successfully draw the circuit but I am not quite ...
33 views

### Calculating the time to perform work on rolling shutters

I have rolling shutters, e.g.: I am trying to determine how much time it takes to raise/lower the shutters a specific amount. (Because of the physics involved, the time is non-linear relative to the ...
22 views

### What difference does it make if a molecule has odd or even parity?

I've been reading a lot about term symbols and spectroscopic notation, but I must have missed the part about WHY a molecule's evenness or oddness matters, in terms of spectroscopy or whatever...
12 views

### What is the “single pulse radiometer equation”?

This document https://arxiv.org/pdf/1601.03547.pdf refers to the “single pulse radiometer equation”. Apparently, it’s used to calculate the flux of radio transients. What is the “single pulse ...
70 views

### Can a CFT have multiple primary operators with same scaling dimension and/or spin?

In CFT ($d>2$), 2-point functions (between two scalar primary operators, for example) vanish unless the operators have same scaling dimension. This leads me to wonder whether a CFT can have two ...
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### Distance and time contrasting results

I know the thing I am missing is right in front of my eyes, please help me see it, I see this equation $x_{final} = x_{initial} + v_{initial}t + \frac{1}{2}at^2$. I want to find the free fall distance ...
37 views

### If I saw two gears turning in front of me, how would I know which of the two has its own turn? [closed]

If I saw two gears turning in front of me, how would I know which of the two has its own turn? In other words, one gear rotates another static gear. How do I know which gear has its own movement?
19 views

### Calculating electrical circuits [closed]

[![Electrical circuits calculations]] : Electrical components calculations https://i.stack.imgur.com/8HoSr.jpg
38 views

### Solenoid and induced electric fields

Let us suppose there is a solenoid which has $n$ turns per unit length the current is varying with time as $I =kt$ where k is a constant if the current is flowing then there must be induced electric ...
27 views

### Intensity and frequency relation [closed]

Two harmonic sound waves, of equal intensity but at different frequencies, one at $800\ Hz$ and the other at $600\ Hz$, impinge at the ear of a listener simultaneously. What two frequencies does the ...
19 views

### Resonance frequency with metal

I've made an experiment with resonance frequency of a LC circuit. One part was to place a metal (I think iron) in the middle of the induktivity of LC circuit. I measured a higher resonance frequncy as ...
34 views

### Electrostatics and Magnetostatics as Field Theories ( isn't the Coloumb law depicting an instantaneous action at a distance)

Take the formula for Coloumb's law. It does not show in any case as to how the static field propagates. What I can feel is that the field of a static charge is ever prevading from the time the charge ...
27 views

### What does Newton mean by 3 kinds of centripetal force?

In his book "Philosophiae Naturalis Principia Mathematica", Newton writes in Definition V The quantity of any centripetal force may be considered as of three kinds; absolute, accelerative, ...
93 views

### Why is the Lagrangian defined as $L=T - V$? [duplicate]

Please try to provide a sufficient answer, and when it is just „because it satisfies Newton‘s equations“, please try to give an example or explain it. If you know it, I would be very happy if you ...
41 views

### How to measure the lifetime of a particle experimentally?

I'm wondering in experiment, how can one measure the lifetime of a particle, because it is a very short time. Also, I'm wondering how experimentalists measure the mass of the particle, which is also ...
35 views

### Computations and physical processes

Can computation be accomplished using any physical process? For simplicity let me restrict myself to the computation of performing addition. I am aware that mechanical calculators just use Newtonian ...
28 views

I'm doing some adiabatic and super adiabatic evolution using python but without success, the super adiabatic to be more precise. The problem is the way I've manage to write the super adiabatic ...
29 views

### How does a coaxial cable feed power (current) into an antenna using only one conductor? ( LogPer Antenna for ex )

I am trying to follow the power that feeds an antenna from a coaxial cable. I found this link where it explains how an dipole antenna radiate, and if I understood correctly it is used a symmetrical ...
58 views

### Why does ground reaction force decrease at the start of a vertical jump?

I don't understand why reaction force would decrease at the start of a countermovement jump. I've tried looking at this diagram and considering moments and how lowering the position of the center of ...
22 views

### Temperature dependent heat capacity and entropy

this problem is often presented as a simple demonstration of relationship between the heat capacity at constant volume $C_V$ and entropy $S$. Let's say the heat capacity $C_V$ is equal to $a T + b T^3$...
45 views

### Will a tennis ball tossed straight up in a airplane cabin move towards the tosser or will its distance from the tosser remain the same? [duplicate]

If I am in a pressurized airplane cabin and I toss a tennis ball into the air, will the ball move towards me? My thinking is that though the ball is in an air bubble that is moving as a whole at the ...
17 views

### Spring block system on a rough surface [closed]

Suppose we have a given a block of mass m connected to a spring of spring constant k and kept over a rough horizontal surface having coefficient of friction u.Initially the spring is compressed by d (...
36 views

### When matter and antimatter meet and annihilate, is that considered 'decay'? By the EM, weak and strong forces simultaneously?

Matter-antimatter destruction is 'decay', correct? And since antimatter particles are considered the opposite of matter ones in every way, not just in terms of EM charge, does that mean they are ...
30 views

### Net torque in a system [closed]

I have a shaft that is fixed on one end and has a rotating head with 4 fans attached to it . Lets say there a propulsion device pointed perpendicular and attached to the surface of the fan in two of ...
47 views

### How can we add torque acting at two different points? [closed]

How can we possibly add the torques acting at two different points?
27 views

### How does water move out of the way/around an object moving under water?

Let's say a torpedo moved under the water. Water is virtually in-compressible right? So what happens to the water in front of the torpedo as it pushes forward? It has to somehow move out of the way, ...
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### Help understanding equations of motions for a line element in their full generality

(Note: I am crossposting this from https://math.stackexchange.com/q/3740738/) Let us work with these definitions $L=\sqrt{dAdB}$ and \$S[A,B]=\int_{\Delta \lambda}\sqrt{\frac{\partial A[\lambda]}{\...