Most active questions
199 questions from the last 7 days
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How do we know what's IDEAL if we have never seen it?
Almost everything I learn in high school considers an "Ideal System".
When dealing with classical mechanics, air resistance, friction, and a lot of other cool, unpredictable stuff are being ...
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12
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7
answers
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Where is potential energy stored in a human body?
Where is potential energy stored in a human body? See, humans need energy to live. Using this energy we can do work, so this is potential energy. When we raise a body to a height $h$, then the ...
- 145
9
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7
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537
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Can we "pick up" an absolutely smooth cone off the ground? [closed]
I came up with the following problem: imagine an absolutely smooth cone with its circular face in contact with the ground. Is it possible to pick it up? Here are the detailed requirements:
The cone ...
- 309
12
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5
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Is white light a bunch of photons or a messy electromagnetic wave or both?
I'm a layperson so I hope you'll excuse my naivete. I have this notion that white light is made of many different frequencies. When I think about them being photons I can imagine them all bunched up ...
- 229
8
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2
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466
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Trajectory in a two-body system (one body fixed)
Is it possible that for same distance (from the fixed body) and same velocity, but different launch angle (say the angle of initial velocity vector), you get different states of the system?
By states ...
- 918
5
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3
answers
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Is EM radiation from a domestic main electric supply harmful?
Pardon me if this not exactly the right site for asking this question but one of my friends sleeps in a room directly next to the main electric supply of his house (220V, 50Hz in India) and insists ...
- 61
8
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4
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Can photons of energy $\hbar\omega$ excite an atom with an energy gap $\hbar\omega_0$ if $\omega\neq\omega_0$?
Consider a two-level atom, with ground state $|g\rangle$, excited state $|e\rangle$, having an energy gap $\hbar\omega_0=E_e-E_g$. Assume that the energy levels are sharp (i.e., no level widths). Let ...
- 12.5k
13
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1
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592
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Is there a rigorous equivalence between the ball-on-hemisphere and falling rod problems?
These are two well-known problems in classical mechanics that yield the same critical result:
Problem 1: Ball on a Hemisphere
A small ball of mass $m$ is placed at the top of a smooth (frictionless) ...
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11
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1
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Why does a mosquito net block the breeze?
When my window is fully open, I can feel the breeze from outside. But when I put on my mosquito net, the breeze gets blocked almost completely. Why does mosquito net block the breeze, even though its ...
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6
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2
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In quantum mechanics, why is the perturbed state orthogonal to the unperturbed state?
In perturbation theory, we may write the full wavefunction as
$$|\Psi\rangle = |\psi^0\rangle + \varepsilon |\psi^1\rangle + \mathcal O(\varepsilon^2).\tag{1}$$
Here I'm focusing on a single energy ...
- 1,300
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4
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When the frequency ceases to exist
As long as a frequency has a wavelength and an amplitude, it can be called a frequency.
If I look to the anatomy of a frequency, what happens if a frequency transforms to a wavelength reduced to 0? Or,...
3
votes
2
answers
508
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Electric field of bound charges
I'm a physics student taking a first course on electromagnetism. I can't figure out how bound charges (or polarization charges) must be thought of. As I've thought to understood until now, in ...
- 601
3
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2
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573
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How does Hookes' law predict that a guitar string's frequency is inversely proportional to its length?
Starting with a spring that obeys Hooke's law,
if we replace it by a spring half its length, of the same uniform massless material, its spring constant (stiffness coefficient) will be doubled,
which ...
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5
votes
1
answer
148
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Does the value of the gravitational constant change due to dark matter?
Dark matter possess its own gravity. So doesn't it would mean that we will obtain different values of gravitational constant by doing experiments at different places?
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5
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1
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Interpreting Curved Spacetime
I understand that gravity is not a force, but instead that mass/energy curves space around them and hence, a object near some considerable mass, though always is travelling in a straight line in it's ...
- 918