# All Questions

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### Inconsistency with electrostatic energy formulas

The energy of point charge configuration can be written as: $$W = \frac{1}{2}\sum_{i=1}^{n}q_{i}V(r_{i}) \, ,$$ which can take both positive and negative values. However, when we integrate the ...
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### How much work can the human body do before dying of exhaustion

If we could assume: We don't increase our energy from absorbing food. Our human example in scope isn't starving or suffering from malnutrition. I mean how much work can we do until the body would ...
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### Machine readable database of gamma lines

Friends of mine did a lab experiment where they recorded $\gamma$-spectra in the range from 0 to 1500 keV with a soil sample. The data contains some background and a couple sharp peaks at different ...
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### Need to know height of wave generated by spherical object falling into water

Working with an architect at present.I need to know the height of wave/ripple that would be created by a spherical object weighing approximately 10 tonnes and measuring 42 metres in diameter falling ...
4k views

### How Special Relativity causes magnetism

So my physics teacher assigned us an article about how special relativity causes magnetism in a wire with a current, even with the low drift velocities of electrons in a current. It seemed that the ...
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### Infrared light and heat

I know that mid wave IR, long wave IR, and far IR are all infrared light that we feel as heat. Often, even when it is cold and windy, if I face the sun in a sunny spot it feels like it is 80 degrees F ...
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### Quadratic Casimir operator of higher dimensional $\mathfrak{su}(3)$ representations

In higher dimensional representations of $\mathfrak{su(3)}$, what will be the quadratic Casimir operator? Is it same as in lower dimensions or different?
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### Smoothed particle Hydrodynamics (SPH), changing length of smoothing kernel makes sim unstable

I am trying to simulate water for a video game. Now I need to make the smoothing length .1 of it's original value, however the simulation explodes. What constants and by how much should I change ...
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### Neck size of wormholes in shape dynamics

As far as a dilettante like me knows, in shape dynamics, black holes are really wormholes. What it the expected diameter of the necks of such wormholes (both for regular holes resulting from the ...
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### How does this spool have an angular acceleration opposite to its acceleration?

Consider this spool. It rests on a rough horizontal force. The green lines are the ground, and a line parallel to the ground. The spool is pulled without sliding by the thread (with tension T), with ...
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### General Solution to Linear Schrodinger equation

I am trying to find a solution to $$\displaystyle \left[-\frac{1}{2}\nabla^2 - \frac{2}{r} + C(r)\right]\phi(r) = E\phi(r)$$ where $C(r)$ is a known function of r. I am just looking for some help on ...
58 views

### Spinning rubber ball with equatorial ridge

I have this rubber ball with something like a very slight equatorial ridge (sort of like Saturn's moon Iapetus) which I often spin around on my desk. I keep noticing that no matter the inclination of ...
381 views

### Is it really possible to “discover” the speed of light with a microwave oven?

I've seen a number of sites/videos online that describe a method for measuring the speed of light, using a microwave oven and a chocolate bar. For example, this video on youtube. The basic idea is to ...
212 views

### Clarification on factors of $c$ in the Lorentz' force

I was told that Lorentz' force is given by $${\bf F}= q{\bf v} \times {\bf B}.$$ But I have read that it is given by $${\bf F}= \frac{q}{c}{\bf v} \times {\bf B}.$$ Why have these two relations ...
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### Constant $c$ in Lorentz force [duplicate]

I met some of examples of force in studying classical dynamics, and Lorentz force was represented as $$\mathbf{F}=\frac{q}{c} \mathbf{\dot{r}} \times \mathbf{B}$$ I've searched for meaning of $c$, ...
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### Units of Lorentz Force Explanation [duplicate]

The Lorentz Force for electromagnetism is obviously $${\bf F}=q({\bf E}+{\bf v}\times {\bf B})$$ And according to Jackson, the B-field (for a charge moving relative to our frame) is proportional to ...
24 views

### Can the use of a magnetic compass be inconsistent with Galileo's Relativity Hypothesis?

I just read Galileo's Relativity Hypothesis from this website: http://physics.ucr.edu/~wudka/Physics7/Notes_www/node47.html It states that - "any two observers moving at constant speed and direction ...
375 views

### Heisenberg XXX time evolution operator for three qubits

I've a problem to reproduce the result in equation (4) on page three of this paper: http://arxiv.org/abs/0802.2588. So far I've understood that they apply a Heisenberg XXX interaction between ...
22 views

### How to understand particle decoupling in the early universe?

We often say that when the rate of some interactions, say the beta decay and electron capture, are slower that the rate of universe's expansion, then the corresponding particles, say neutrinos, ...
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### Help to find a simple setup for optical surface topography

I'm looking for some help from someone expert in optics to create an inteferometry based setup to map the surface of a small object. This is for a small lab project so I'm not looking for a really ...
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### Oil Lamp Dynamics

Here is a photo of an oil lamp I am making. I am facing a few problems.first how its made. Its a glass bulb with a custom fit plug made out of aluminium.The bulb balances by way of a neodymium ...
2k views

### Is electricity instantaneous?

My question is basically what exactly is electricity? I've simply been told before that it's a flow of electrons, but this seems too basic and doesn't show that electricity is instant. What I mean is ...
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### Safest place to store a laptop in a car? [on hold]

I sometimes drive my younger brother to his robotics club meetings and he brings a laptop to work on. He weighs about 70 lbs (32 kg) and is about 5'3" (1.6 m) tall. The laptop weighs about 20 lbs (9 ...
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### What subatomic particle is a blackhole composed of?

In a black hole, what is the "state" in which the mass that is present is in? Are they there as tightly packed neutron or soup of quark or are particles broken down into 10D strings and coiled as ...