Skip to main content
6 votes

Rest Mass Energy

The problem with asking for an intuitive explanation is that intuition is not an objective feature of an explanation. Intuition is something that is personal and it is developed individually from ...
Dale's user avatar
  • 102k
3 votes

On the existence of Gravitational energy in GR

It depends. As you mentioned, there is no stress tensor for the gravitational field. Hence, we can't localize gravitational energy. In this specific sense, it is common to say there is no ...
Níckolas Alves's user avatar
2 votes
Accepted

Rest Mass Energy

In physics today, mass always refers to rest mass. When referring to other types of mass, such as "relativistic mass" or "invariant mass," one always adds an extra qualifier to be ...
Prahar's user avatar
  • 26.2k
2 votes
Accepted

Paradox? Why does energy conservation appear to be violated in this simple geared system?

A mass of M attached to the larger gear with radius 2R should balance a mass of 2M attached to the gear/pulley with radius R, because the torques are equal, just like a lever with one arm twice as ...
Dale's user avatar
  • 102k
2 votes

How to understand $W=pc$ in Feynman's Lectures on physics?

$$W=\sqrt{p^2c^2+m^2c^4}$$ approaches $W=pc$ for $p\gg mc$ and $W=mc^2+{p^2\over 2m} = mc^2+{1\over 2}mv^2$ for $p\ll mc$.
my2cts's user avatar
  • 24.5k
2 votes
Accepted

How to understand $W=pc$ in Feynman's Lectures on physics?

$pc$ is the total energy of a massless relativistic particle, like the photon. Electrons do have mass, so what's the catch? Well, if the momentum of the electron is very big, then we can neglect the ...
Gabriel Ybarra Marcaida's user avatar
1 vote

What is the difference between a reversible process and an equilibrium? What is the relationship with entropy and energy?

The equation \begin{equation} dS = \frac{dQ_{rev}}{T} + dS_{irr} \end{equation} Is incorrect. It should be $$dS=\frac{\delta Q}{T} + dS_{irr}\tag{1}$$ That's because the differential change in entropy ...
Bob D's user avatar
  • 72.5k
1 vote

What happens if you factor in the energy required to switch between the reservoirs and insulating stand of the Carnot engine?

The work of this switching process surely consumes...energy There is no theoretical reason why a mechanism that continually repeats the same cyclic motion could not do so forever with no energy input....
Solomon Slow's user avatar
  • 14.6k
1 vote

Paradox? Why does energy conservation appear to be violated in this simple geared system?

You asserted that the gear in the middle doesn't matter, but it does. When the gears are turning, you will have a ridiculous situation, because the turning of the gear in the middle cannot be ...
naturallyInconsistent's user avatar
1 vote
Accepted

Solution to infinite particle creation in EM by classical sources

The previous example gave a short and quantitative answer. I'll try to be more qualitative. Perhaps the most famous example of this is the Schwinger effect. I'll give a brief overview of the physical ...
Níckolas Alves's user avatar

Only top scored, non community-wiki answers of a minimum length are eligible