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Apr
13
comment Why can lights(photons) bends in a curve through space without mass?
@MarkHurd: The observers will see the bend because it is effect of gravity. Whether they are "in" the gravitational field (whatever it means) does not matter.
Apr
12
comment Why can lights(photons) bends in a curve through space without mass?
@MarkHurd: According to observer in non-accelerating reference frame with no gravitational field light is not bent. The axiom does not talk about accelerating reference frame in gravitational field. It says that two distinct cases, one with gravitational field and one with no such field, but using accelerating reference frame, look the same.
Apr
11
comment Why can lights(photons) bends in a curve through space without mass?
@PoomrokcThe3years: Actually, the whole curvature of space-time is derived from simple principle of equivalence between gravity and acceleration of reference frame. From which it follows rather directly that light shouldn't be exempt from gravity.
Apr
11
comment Why can lights(photons) bends in a curve through space without mass?
Photons don't have rest mass, but they do have relativistic mass. Since it's equivalent to energy, it's a trend to just rewrite all the formulas to just use energy, but as far as Newtonian formulas can be used, the mass in them is relativistic mass and non-zero for photons.
Apr
11
comment Why can lights(photons) bends in a curve through space without mass?
@Ruslan: Since relativistic mass is equivalent to energy anyway I understand it's easier to rewrite the formulas for energy instead, but as long as we are attempting to reuse formulas from Newtonian dynamics here, relativistic mass is needed in them.
Apr
11
answered Why can lights(photons) bends in a curve through space without mass?
Apr
11
comment Why can lights(photons) bends in a curve through space without mass?
@ColeJohnson: Fortunately, photons do have mass (equal to $\frac{h\nu}{c^2}$), so you don't get that. They just don't have rest mass.
Apr
11
comment Why can lights(photons) bends in a curve through space without mass?
@ColeJohnson: Yes, if you plug in $0$ for $m_1$, you get $F_g = G\frac{0 m_2}{r^2}$, but you also get $a_g = \frac{\frac{0 m_2}{r^2}}{0}$.
Apr
1
answered Why is it easier to walk diagonally upstairs
Apr
1
awarded  Commentator
Apr
1
awarded  Teacher
Apr
1
comment Why is it easier to walk diagonally upstairs
No. You have to do less work the shorter the path is. The work that goes into climbing is the same in both cases, because only the vertical component contributes to that and longer horizontal path means more work needs to go into overcoming drag (which is small comparable to the work needed for climbing).
Apr
1
revised Why can't helicopters reach mount everest?
added 9 characters in body
Apr
1
answered Why can't helicopters reach mount everest?
Apr
1
comment Why can't helicopters reach mount everest?
@MartinBeckett: Yes, but. With less air, the engines do produce less power and thrust. Due to less drag, an aircraft fortunately needs less of it. But that's not the case of helicopter, which always needs the same power.
Apr
1
comment Why can't helicopters reach mount everest?
@hdhondt: Many aircraft do have trouble in that altitude too. The reason is somewhat more complicated though. I'll expand it to a separate answer.
Mar
5
comment Why does a remote car key work when held to your head/body?
@neonzeon: Except when the fob is in outstretched hand, it is mostly horizontal and should have decent reception while when it's held to one's head, it is almost certainly pointing the flat side at the car, the worst possible orientation.
Oct
3
revised If I am travelling on a car at around 60 km/h, and I shine a light, does that mean that the light is travelling faster than the speed of light?
mark the quote up as quote
Oct
3
suggested suggested edit on If I am travelling on a car at around 60 km/h, and I shine a light, does that mean that the light is travelling faster than the speed of light?
Sep
10
comment Explaining UV radiation to a 6 year old
Since cats and dogs hear higher frequencies than humans, you could try generating high sound in presence of an animal and showing it notices something though you don't hear it. I am not sure whether you could actually generate sound that would not be audible at all though; the dog whistle still generates some audible lower harmonics even when set to highest pitch and computers generally have 48 kHz DA that only allows 24 kHz which might still be barely but audible.