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HNQ
12:40 AM
2
Q: Does an atom recoil when photon radiate?

SergioConsider an atom in the excited state radiating a photon and goes to the lower energy state. But photons have a certain angular momentum, the momentum itself is not defined. In this case, will there be a recoil of the atom due to photon emitted?

 
 
3 hours later…
HNQ
3:38 AM
2
Q: If an earthquake can destroy buildings why it cant kill us according to physics?

ZheerMost Earthquakes with a magnitude (5.5) and higher can damage or destroy buildings, according to my knowledge and expierence i have never seen someone dying from earthquake itself, they die from tsunami, damaged buildings...etc You need much more force to destroy a building or damage it than the...

 
 
12 hours later…
HNQ
3:09 PM
2
Q: How is linear momentum conserved in case of a freely falling body?

ZamWhen an object is experiencing free fall, it has a constant acceleration and hence an increasing velocity (neglecting friction). Thus its momentum is increasing. But according to law of conservation of momentum, shouldn't there be a corresponding decrease in momentum somewhere else ? Where is it ?

 
 
4 hours later…
HNQ
7:25 PM
2
Q: Why isn't temperature definable for a single, classical particle?

Edoardo SerraI read that the relation between temperature and kinetic energy of an ideal gas is only applicable to a large number of particles so that the mean value for kinetic energy has to be considered, so the temperature concept makes sense only as a statistical quantity. But why is that? Using the afor...

 
HNQ
7:44 PM
2
Q: Why do proofs of Bernoulli's equation assume that forces on opposite ends point in different directions?

user3711671 I've read 4 different books and yet nobody explains why forces $F_1$ ($=p_1A_1$) and $F_2$ ($=p_2A_2$) point in different directions. Shouldn't $F_2$ point in the same direction as $v_2$? Since we're assuming that parts of fluid between $a$ and $b$ have the same kinetic and potential energies...

 
HNQ
8:24 PM
2
Q: Kinetic energy vs temperature

Federico TosoI know that macroscopic temperature is a measure of kinetic energy of particles at very low scales (let's call it microscopic kinetic energy). But how can we derive which part of this microscopic kinetic energy gives rise to temperature, and which part instead gives rise to macroscopic kinetic e...

 
HNQ
8:43 PM
1
Q: From Poisson's equation to Laplace's equation

khaled014zI want to understand how exactly $$ \nabla^2 V = - \frac{\rho}{\epsilon_0}$$ turns into $$ \nabla^2 V = 0.$$ Of course it is by setting $ \rho$ equal to $0$ but what does setting $ \rho$ equal to $0$ mean? $$ \int_{S} \vec E \cdot d \vec a = \int_{V} \nabla \cdot \vec E \, d \tau = \frac {Q}{\...

 

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