15
votes
Accepted
Relation between energy and time
There are at least three occasions where the notions of Energy and Time show up together in classical and modern physics.
Probably the most elementary situation is related to the fact that the ...
- 73.8k
9
votes
Is there a wavelength shift between sunlight observed from the ISS versus from Earth's surface?
The atmosphere does not shift the frequency of light, but it does scatter and attenuate the radiation. The graph below shows the relative intensity of solar radiation at the top of the atmosphere ...
- 41.1k
5
votes
Relation between energy and time
Why is energy always related to time in physics.
I don't think it is helpful to describe energy as "always related to time" in physics.
That being said, there certainly are a number of ...
- 21.9k
4
votes
Is the kinetic energy of a rotating system just the sum of the instantaneous kinetic energies of the individual particles?
There's no "linear KE" nor "angular KE", there's only KE.
KE of a particle. The KE of a particle is defined as
$$K = \frac{1}{2} m |\mathbf{v}|^2 \ .$$
You just need to take the ...
- 10.7k
2
votes
Relation between energy and time
The way I like to look at it (and which may or may not give you the same amount of intuition as it does to me) is as such:
Momentum is what gives rise to changes in position. Clasically, a body ...
- 936
2
votes
Accepted
Strogatz's condition on definition of energy
If $E$ does not depend on $x(t)$, then $\frac{dE}{dt}=0$ doesn't give you any information about $x(t)$. Since the entire goal of classical mechanics is to solve for $x(t)$, this means such an $E$ ...
- 51.2k
2
votes
Accepted
Enthalpy at constant pressure/volume
Enthalpy is defined as $H=U+pV$ irrespective of what process the system is subjected to. It, enthalpy $H$, is a state function and in equilibrium thermostatics its definition has nothing to do with ...
- 19.7k
1
vote
Why particle is certain to escape the conservative field when the mechanical energy is positive?
From the comments:
By @naturallyInconsistent
For convenience, we chose to put the conventional dividing line for this thing so that zero is the limiting case. i.e. it is a choice, a very natural ...
1
vote
Confusions in conservation of angular momentum and torque
Oh, I get it. The equation $\tau_z = I\alpha_z$ is not valid for a non-rigid object (even if it is solid and doesn't change forms, if it changes in radius relative to the axis, it is non rigid, as ...
- 61
1
vote
Can siphons improve the efficiency of hydroelectric dams?
No, you cannot gain any efficiency.
Remember the bernoulli equation:
$P_1 + \frac12\rho v_1^2 + \rho gh_1 = P_2 + \frac12\rho v_2^2 + \rho gh_2$
If you have water at rest at $P_{atm}$ on the top, and ...
- 795
1
vote
Why is all matter in the universe, not found at its lowest state of potential energy?
theoretically, if some matter loses energy (it will go to a lower
potential energy state), other matter will absorb this energy (it will
go to a higher potential energy state).
The key to all this is ...
- 6,102
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