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1d
revised Energy efficiency for common fuels
c is 3E+8, c^2 is 9 E+16
Nov
25
comment How much air needs to be displaced to generate an audible sound?
As long as the pressure wave peak stays below ambient pressure, the waveforms would be mirrored. You indeed can have 2 atmospheres of overpressure but not underpressure.
Nov
21
answered How much air needs to be displaced to generate an audible sound?
Nov
21
comment How come neutrons in a nucleus don't decay?
@Jonathan. : good question. The neutron doesn't even know what its end state should be. At the quantum scale, things literally don't stay put. All the quarks that make up a neutron are moving around the nucleus, and interact with other particles nearby. Now it may happen that one of these interactions produces an electron. If that electron stays together long enough and escapes the nucleus (i.e. its probability of being in the nucleus drops to virtually zero), the remaining quarks in the nucleus together will have the properties of a proton - be a proton.
Nov
19
comment Is it possible to create a parachute large enough to stop all velocity?
Keep in mind that KSP has a halfway decent orbital model, a somewhat flawed model of the mechanical forces between your rocket parts, and a very flawed aerodynamical model. Unfortunately, parachute physics are primarily aerodynamic.
Nov
17
comment If we traveled at almost light speed with a mirror in hand
@coteyr: Time too behaves non-linear at those speeds. Light does travel at light speeds from the mirror to your eyes. We've measured it. Look up the Michelson Morley experiment, which famously killed Ether theory (hence Carl Witthoft's comment). If the speed of the source would matter, the earth moving around the sun should matter too. It didn't.
Nov
17
comment If we traveled at almost light speed with a mirror in hand
@coteyr: At relativistic speeds, you can no longer add up or subtract speeds as if they're simple numbers. Light coming from the mirror behind you, being light, travels with speed c towards you. Your own speed is irrelevant, it can be 99% of c or 0.00001% of c. Results are identical.
Nov
17
comment If we traveled at almost light speed with a mirror in hand
In modern physics, speed is binary. Either it's lightspeed or it's less than lightspeed. In your case, it's less than lightspeed. Without loss of generality, you may assume you're travelling 100 km/hour.
Nov
10
awarded  Yearling
Nov
3
awarded  Nice Answer
Nov
3
comment Do we take gravity = 9.8 m/s² for all heights when solving problems? Why or why not?
Relevant meta. Consensus seems to be SI good, natural too (where appropriate), CGS is edge case.
Nov
3
comment Does a cooling mass lose mass as it radiates?
Thanks for the formatting, but I think d/dt (c²) is negligible ;)
Nov
3
answered Does a cooling mass lose mass as it radiates?
Oct
20
comment Is the particle reaction $π^- + p \to K^- + Σ^+$ possible?
That's a good reason why it's not allowed. Of course, there could be multiple reasons, and it's not like nature checks them in a specific order.
Oct
15
answered Planets and Pluto? Neptune?
Oct
15
answered Can Thermal Energy be converted into usable energy?
Oct
12
comment Benefits of rear spoiler in cars
The problem with this theory is that you need to exert an upward force on the air over the spoiler to get downforce, but to decrease that low-pressure zone you'd have to send air downwards. A spoiler beneath the car seems to make more sense.
Oct
12
comment Is it possible to start fire using moonlight?
Your argument about black-body radiation from the moon holds for a new moon. I'll bet that agrees with your gut feeling. With a full moon, you're discussing reflected sunlight which isn't in thermal equilibrium with the moon surface.
Oct
1
comment Why do rockets jettison fuel tanks?
Actually, as most Kerbal Space Program players know, you don't need extra engines even if you have stages. You just have to attach the tanks to the side instead of stacking them. In reality, there's another benefit: if you have multiple engines, you can optimize them for different ambient pressures and trust levels.
Sep
26
comment Machine to identify substances
That "White laser" might be hard to source.