Confusion Definition and 1000 Threads

What is time derivative of angular velocity ( measured w.r.t. an inertial frame ) of a rotating co. system w.r.t. the same rotating co. system? I think a person sitting in a closed rotating box feels the an object at rest w.r.t. him as rest. He doesn't observe the angular velocity of the...

I caught this on the BBC iPlayer and I'm somewhat puzzled. The report - brief though it is - seems to suggest that meaningful information can be transmitted via quantum entanglement. I've always understood this to be impossible as it would violate Special Relativity. Or can quantum entanglement...

Homework Statement Accidents at a busy intersection follow a Poisson distribution with three accidents expected in a week. What is the probability that at least 10 days pass between accidents? Homework Equations F(X) = 1- e-λx μ = 1/λ The Attempt at a Solution Let x = amount of time between...

Hey everyone, first, let me say I understand the complement rule. Where I am confused is over the integration. My professor said that suppose you have a continuous cumulative distribution function F(x) = 1-e-x/10, if x > 0 (0, otherwise). And suppose you want to find P(X>12) you can use the...

In the attached pic,it is shown that the coordinates of point B are (a cos theta, a sin theta) ,but shouldn't it be (-a cos theta,a sin theta)? Can anybody please help?

Hello, Over the past couple of weeks I have been working my way through the basics of physics on my own. I've just arrived at work and energy and there is one thing that confuses me a little bit. Let's say I have a 25kg box on a sidewalk. I go to push it and I ultimately push it 5m east (lets...

I understand that gravitational acceleration is independent of mass. However, I've seen a common mathematical description of this that I can't help but find circular. I suspect that there's an error in my thinking that I'm hoping someone can point out for me. It goes like this; ##F=mg## but we...

From the reference frame of the earth, the distance between the surface of the Earth and the muon is longer, but the muon survives because time for the muon is slowed down. From the reference frame of the muon, the time experienced by the muon is not slowed down but the muon survives because...

I'm sure there's an obvious answer to this, but this problem has been confusing me for some time. Imagine there were a massive object attached to the end of a crankshaft. A force is applied to accelerate the crankshaft, causing the mass to oscillate. Assuming there is no friction, what would...

Say I want to investigate the rate of crime by the density of police inside a city. The sampling unit is per city. So according to a problem I saw, it claims that we can model it by ##log(\mu_{i})\sim PoliceDensity_{i}+log(PopulationSize_{i})## Where ##\mu_{i}## is the mean count of crime in...

Why is the equation Power Loss = I^2*R rather than Power Loss = V*I? What I mean is why use I/R to represent V? Also if Power Loss is equivalent to V*R, doesn't step up transformers which creating higher voltage also cause Power Loss to increase which contradicts to textbooks stating that power...

Hi everybody, I apologize if something like this has been asked before but I have been unable to find an answer through searching. If a weight is carefully added to a moving cart then the cart should slow down due to conservation of momentum. How is it that the cart has accelerated without a...

This past semester, I just took an introductory course on G.R., which translates to a lot of differential geometry and then concluding with Schwarzschild's solution. We really didn't do any cosmology. However, one of the themes that kept creeping up again and again is that in 4-dimensions...

Sorry if this is the wrong place to post this, but I wasn't sure where exactly to put it. When we calculate the force on a closed loop of current-carrying wire in a uniform magnetic field, We calculate the line integral of the loop to be 0. However, when we evaluate the line integral for an...

I've got confused over a topic in my physics textbook (Fundamentals of Physics). The textbook says if a charged particle is enclosed by a shell of uniform charge, there is no electrostatic force on the particle from the shell. I don't firmly get this, as the book uses a confusing reasoning for...

I know variations of these have probably been asked numerous times before, but I'm having trouble with this specific scenario. Imagine the classic Train Paradox, except instead of lighting strikes we have an observer at the centre of the train shooting laser pulses towards the rear (Event E1)...

1. The problem statement Relevant equations: I am confused. When dealing with Ampères law: dl is supposed to be the length element? Like when we have Gauss' law for electric fields and we use a circular Gaussian surface, we have E(4πr^2)=Qenclosed/ε So in this case, when we have a circular...

Hello! I am a bit confused by the Doppler effect. Based on the formula it seems that if the source moves towards me with speed ##v## I hear a frequency ##\nu_1## but if I move towards the source with the same speed ##v## I hear a different frequency ##\nu_2##. However according to the...

Homework Statement Hi guys, I have am having a problem with the questions below. what do they mean by show ## B_{perp}=B sin\theta ## I mean I know it a silly question, and my first thought is just use socahtoa, or am I missing something. The question from there on is straight forward...

Is forcing a closed system to expand (e.g. by pulling out a piston), causing it to cool, work done to the system or work done by the system? I assume it was work done to the system, but that means the first law of thermodynamics formula no longer balances if you assume an adiabatic change...

Homework Statement I have several question regrading with this post . 1.) For BC and CB , we could see that it's far end pinned / roller supported , so , shouldn't be the K = (3/4)(EI / L ) ? 2.) I don't understand how the carry over factor works (in the second picture) Homework...

One way to see that spacetime is curved is to try and draw a "rectangle" in spacetime (see the figure in the Feynman lectures, ch 42.7): If I wait for 100 seconds and then move upwards on earth, I end up at a different point in spacetime than when I first move upwards and then wait for 100...

Homework Statement I am working on this problem: The formula I am given in my notes is: I found a website which explains this problem, and they give this formula: But then, their answer is: And I don't see how they went from sqrt(8) to 2 on the numerator. I am confused which formula to use...

1. The problem statement, all variables, and given/known data I have a single loop RL circuit with no source. I am given the the inductance of 3mH, as well as that energy storage is as follows 1 J @ t=0 and 100mJ @ t=1ms. No current is given. I have to find R. I don't need the answer just some...

I'm having some confusion about the creation of magnetic field lines. How I understand it so far, is that a magnetic field is basically an electric field viewed from a relative point. I don't have a great understanding so far, as I just started to learn about it, but I've learned that objects...

Hello, Homework Statement I'm given the following exercise: "A rod with neglected thickness exists. What is the relation between the α,β angles to Euler angles of orientation? α is defined as the angle between the rod and its projection on the XY plane. β is defined as the angle between the...

Hi, I am studying about F ratio and how, as a random variable, it follows F Distribution. So let me explain what confuses me. This is what the theory says -- We draw two random samples $sample_x$ and $sample_y$ from two different Normally distributed populations with equal variance...

Ok, so the title was pretty vague, I'm not sure how to succinctly describe the confusion. Anyway, so I've learned that the power lost is P=I2R, and so by increasing the voltage, as P=VI and is constant, the current will be lowered, and thus the power lost will decrease. I'm confused about a...

Hello, A dude I'm discussing momentum and kinetic energy with says this: "Place two masses in deep space, the only gravitational attraction is from each other. One of the masses is ten kilograms and the other is one kilogram. From Newton's Third Law we know that the mutual attraction is equal...

If I understand correctly, the Planck length, or maybe a tenth of it, is considered the point at which quantum effects mess up any attempt to apply our present physical laws, and so one could not even in theory make a dependable measurement of something smaller. However, I was wondering what...

Hello. I have several confusions regarding Faraday's law of induction. EMF = \int_{}^{} {\vec E \cdot d\vec l} = - \frac{{d\Phi }}{{dt}} = - \frac{d}{{dt}}\int_{}^{} {\vec B \cdot d\vec S} . It means that If the magnetic flux Φ through the closed conducting loop changes in time, electric...

Homework Statement The electron density per area, ##N## for a gas layer of thickness 10 cm can be determined $$n = k \times p \times 2.47 \times 10^{19}$$ For each adjacent sets of pressure data using Matlab, calculate the average energy in keV, the pressure difference in hPa, the energy...

Okay so when there is time-translation symmetry because the metric components do not have any time- dependence, ##\partial_x^0## is a Killing vector. I'm just confused what this means explicitly, since a derivative doesn't make sense without acting on anything really? But by 'spotting the...

Hello all, I am taking a thermodynamics course and unfortunately my professor is not very instructive. I have attended every class and I still feel lost. I was wondering how it is possible to find heat capacity if both the pressure and the volume are changing? I was under the impression that...

Homework Statement A chemist dissolves 16mmol of a nucleoside diphosphate, CDP, in 1L of an aqueous solution containing Mg2+ and buffers the solution at pH 8.7. The chemist monitor the reaction by measuring the amount of inorganic phosphate produced. No reaction is detected for 30mins, then the...

Homework Statement Hi guys, I am having trouble with ex 6.1 and 6.2. I am listed my ans below, and shown working. Could someone please advise. First I am not sure why I have to start with $$x=Ae^{imt}$$. Why cannot start with $$Ae^{px}$$? Homework EquationsThe Attempt at a Solution i) $$Aux...

In my textbook.In some question gives me angular speed as ( )rev/s.I know that its the frequency (f).But some questions It says angular velocity and says rad/s. Interesting thing happens when the textbook says in angular speed and I use f and then using w=2πf and then continue I get wrong...

example code from python-course.eu def factorial(n): print("factorial has been called with n = " + str(n)) if n == 1: return 1 else: res = n * factorial(n-1) print("intermediate result for ", n, " * factorial(" ,n-1, "): ",res) return res...

Homework Statement I have three questions spanning three different situations, but each deal with the single concept of electric flux. Problem 1: Write an expression for the net electric flux through the entire surface in terms of the area vectors and the electric field E. Problem 2...

If light is pure energy, then how can gravitational lensing work? And if light has some mass, how can it change directions instantly when it is traveling through a prism? My high school science teacher had no answer 45 years ago.

Homework Statement Hi guys, I am having a issue with the notation of this question. I can workout what to do, but I don’t understand what is $$C^+,C^{++}$$ Could someone please explain. My thought is maybe is 2 carbon atoms bonded together? Homework EquationsThe Attempt at a Solution

I found it somehow tricky to understand average speed and average power in mathematical fashion. I suppose general idea of taking average of some quantity is: sum of all values/number of values. how that idea fit's into idea of average speed=distance traveled/time traveled similarly, average...

Hello, everyone! When thinking about an issue pertaining to a work of fiction, does the "primary vs secondary sources" rules matter when coming to a conclusion? Does this wildly held belief hold up in the world of fiction where things are up for interpretation? An example would be, at the end...

Homework Statement So in the attachment you'll see a picture taken from a linear algebra book where a linear system of equations is presented in the equivalent augmented matrix form. I'm confused about the representation of the first equation in the augmented matrix. What happened to the...

Okay, so I have just started with simple harmonic motion(SHM). So the equation of displacement in my textbook is given as: X= ACos(wt +x) where A is the amplitude X is displacememt from mean position at time t w is angular frequency x is phase constant...

Homework Statement This is just one of the example problems in my book which is already solved for me, but I don't really understand their solution which I'll post here: They start out with assuming Vin is very negative, which makes D1 turn on and makes Vout=VD,on+Vin. THen they solve for...

Homework Statement I'm working through some exercises in which I'm supposed to convert various units of speed from SI units to other units Example: 0.4m/s into km/h Homework Equations The Attempt at a Solution Having checked, I know my answer to be (to 3 significant figures) correct. My...

If a wheel is freely rolling on the ground (not torque driven, but by a force acting on its center of gravity) towards the right, the friction force on the bottom of the wheel would be acting towards the left. What if the friction force was equal to the force acting on the wheel's COG? Then the...

I find it somehow confusing to imagine why m*a=-k*x is "generally valid". that minus sign bothers me. Imagine I raised a bob to some height (ex. from the left side) and then released it. from that moment till the moment where it reaches equilibrium position m*a and restoring force have same...

Why is ##\theta## a scalar whereas ##d\theta## a vector ?