# All Questions

1 views

### Vector Calculus in non orthogonal basis

Given a general spacetime, namely a metric, is there a standard way to define vectors and products between them? What I am actually interested in is how to generalize the familiar dot/cross product ...
11 views

10 views

### Why is radiance a measure for how bright an object appears if it is constant regarding the distance to the light source?

Radiance is flux per solid angle per unit area normal to the beam. Let’s say, you look at a piece of paper that is lit by the sun. Now you move twice as far away, the flux is then reduced by four due ...
22 views

### Steering a motorcycle

From my experience riding, at low speeds (between 0 and 10 mph) you mostly steer the bike with the handlebars. What I mean by this is if you want to turn left you rotate the handlebars ...
48 views

### What is matter made of in the light of Quantum Mechanics?

I've always wondered what matter (particles, force particles, etc.) was actually made of considering the fact that quantum mechanics has shown us that particles can actually act as a probabilistic ...
23 views

### Boundary problem with forced vibration [on hold]

Consider the forced vibration of a string governed by $$\frac{\partial^2 u}{\partial t^2} = \frac{\partial^2 u}{\partial x^2} + Q(x,t)$$ subject to the boundary conditions $$u(0,t) = A(t)$$  ...
17 views

### Are muon energies quantized?

I'm working on a problem that asks: For a central charge $Ze$, obtain an expression for the radius $r_n$ of the $n$th muonic orbit. Express this as a multiple of the radius $a_o$ of the first Bohr ...
228 views

### Other explanation for cosmological redshift?

I'm interested if any of the following explanations have enough predictive capability to explain the observations we see today. The claim is that the Universe is not expanding, and that red-shift of ...
18 views

### Do the strong magnetic field affects the Human Brain? if yes, then how? [on hold]

How this phenomenon occurs tell in detail
38 views

### Force balancing - Newtonian mechanics

If a horse pulls the carriage, the carriage should pull the horse with equal force (Newton's third law), then how does the whole system move? I drew the free body diagram but not yet figured what ...
12 views

### Magnitude of magnetic field due to current in a semicircular wire at a specific angle θ? [on hold]

My task is to find the magnitude of magnetic field due to a current going in a semicircular wire at an angle θ. Now, using Biot-Savart law, I have the current equation at dB = (μ0 I/4piR) ...
25 views

### Flow in the strip $0 < x < \pi/2$, $y > 0$ [on hold]

Could anyone please explain how to show that a complex valued function represents a flow? For example, how does one show that $\Phi(z) = \sec^2 z$, where $z = x + iy$ with $x, y \in \mathbb{R}$, ...
49 views

### Is it possible to have a mathematical mind, though somewhat failing in physics? How to rectify it then? [on hold]

I'm inclined to think I'm kind of good at mathematics, I've also been told so, quite often, by both my professor and friends. After all, it most importantly is my greatest passion. It is true as well ...
49 views

### Point, bar and a mass

This question is a simplified down version of my first question to understand the core essentials of my question. The question now stands with the simplified diagram: There are three things in the ...
27 views

### Force on ball going around loop

Suppose I have a ball of mass m going around a loop. It is radius $r$, and rolling without slipping. Half way up the loop, what is the force in the $x$ an $y$ direction if it is at velocity $V$? I ...
20 views

### Where does the polarity of particles come from? [duplicate]

Going though current lessons, I can clearly see that some particles, electrons, are charged negatively and other, protons, are charged positively. Where does this polarity come from? Knowing that ...
14 views

### How to model the impedance of a coil with a dielectric slab on the top

I have sketched what I meant in the image below. Were there no dielectric slab, the coil could have been simply modeled as an inductor. But I am not sure what the impedance can be if there is a ...
44 views

### Representations of Galilei group

Show that the operator $U(\alpha, \beta) = e^{i(\alpha \hat{x}^2 + \beta \hat{p}_{x}^2)}$ can represent the space reflection of the 1D Galilei group: $x \to -x; t \to t$. I don't really know ...
18 views

### Voltage changes under load across parallel pack [on hold]

I have 97 LiFePO cells in parallel. They've been sitting for days so the average cell voltages is 3.19v. I put a 5A load on the pack at "B". I measure V across "B": 2.80V. I measure V across "A" ...
36 views

A question about memristors: These semiconductor entities have been defined in terms of magnetic flux leakage, and a non-linear relationship to the electric charge that has flowed. In essence, the ...
36 views

### How does matter interact with spacetime? [on hold]

It's easy to see how matter interacts with itself but how does it interact with spacetime which is "not" matter? Einstein showed us that mass and energy cause a curvature in spacetime, which intern ...
34 views

### What is the symbol for the moment of force (torque): $N$, $M$ or $\tau$? [on hold]

Classical Mechanics (Goldstein, Poole and Safko) calls it $N$. Principles of Dynamics (Donald T. Greenwood) calls it $M$. Google calls it $\tau$. So... which is it?
28 views

### Parallel Resistors (special cases formula)

1) A car's rear window defroster uses $n=15$ strips of resistive wire in a parallel arrangement. If the total resistance is 1.4 ohms, what is the resistance of one wire? Solution: I rearranged ...
50 views

### Ray tracing in General Relativity

I would like to find out what one would see at the Schwarzschild radius of a massive non-rotating black hole, if the black hole is surrounded by a bright ring. For that, I would place the observer at ...
31 views

### Force-carrying particles instead of forces

Are there physical theories in which notions of particle are used without the concept of force? I know about gauge bosons, see: http://en.wikipedia.org/wiki/Force_carrier and ...
25 views

### Negative pressure experiments

One method of understanding the physics of materials is to study their properties under the effect of pressure. Under high pressure, new phases can arise. Experimentally, high pressure can be obtained ...
26 views

44 views

### What causes a resistor to heat up?

In the following video clip at 2:10, http://www.youtube.com/v/YslOUw5oueQ , Professor Walter Lewin talks about a misconception people have that the energy going through a wire to a resistor is in ...
14 views

### Driving force in a homopolar motor

I can't really figure out the driving force in the following homopolar motor: http://www.youtube.com/watch?v=w2f6RD1hT6Q I am not convinced by the usual argument involving the Laplace force, so ...
34 views

### What would happen if Newton's Cradle was made of other geometrical objects rather than spheres?

What would happen if Newton's Cradle was made of other geometrical objects rather than spheres? For example, what would happen if it was made of cubes and the contact area was larger?