Ilmari Karonen
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 Apr 22 awarded Good Answer Apr 4 comment Why do travelling waves continue after amplitude sum = 0? @curiousdannii: jpa does have a point; the dynamics on either side of the midpoint would look exactly the same even if you fastened the midpoint to an immobile wall. (In fact, this is how one can show that a wave hitting a fixed boundary will produce an inverted reflection.) So we effectively have two equivalent descriptions of the same motion; one in which the waves pass through each other and combine linearly, and one in which they never interact except through the midpoint, which never moves. Apr 4 awarded Nice Answer Apr 3 answered Why do travelling waves continue after amplitude sum = 0? Mar 28 awarded Nice Answer Mar 28 comment How to interpret the units of the dot or cross product of two vectors? @Ilja: I'm not quite sure what you're asking. Rotating something by 90° surely is a physically meaningful operation; I don't see how it needs any kind of "interpretation". If you like, you can take a stick and physically rotate it 90°, in any plane of your choosing, to see that it's indeed possible and physically meaningful in real physical space. Mar 27 revised How to interpret the units of the dot or cross product of two vectors? added 478 characters in body Mar 27 comment How to interpret the units of the dot or cross product of two vectors? It is, in fact, possible to interpret the dot product geometrically. See my answer for some examples. Mar 27 answered How to interpret the units of the dot or cross product of two vectors? Feb 25 comment How does a spinning object “know” that it is spinning? I suspect you may have hit the source of the confusion here. Given that, apparently, the laws of physics are intrinsically invariant with respect to position, orientation and velocity (= the time derivative of position), it's somewhat surprising that they're not invariant with respect to angular velocity (= the time derivative of orientation). But of course, an extended object with non-zero angular velocity necessarily (either breaks apart or) experiences non-zero centripetal acceleration, which is also absolute. Feb 22 comment Why doesn't an electron ever hit (and stick on) a proton? -1, this doesn't seem like a useful way to answer the question. An electron does not orbit the nucleus in a classical orbit like the moon orbits the earth, and that misconception is precisely the source of the OP's confusion. That's not something you should be reinforcing in the first paragraph. Jan 17 comment How am I able to stand up and walk down the aisle of a flying passenger jet? This does not seem to answer the question in any meaningful sense. Dec 28 comment Why is there an electric field in a wire even though it is a conductor? @1110101001: The fact that some current/voltage source (e.g. a battery, a generator, etc.) is constantly moving electrons the other way, and thus replenishing the field as fast as it decays. Disconnect the source, and the field does disappear very quickly (limited only by the resistance of the wire). Dec 25 comment Do raindrops spin as they fall? True, that part of your answer is correct -- the shape of a raindrop is not the one with minimum drag among all possible shaped. (It also doesn't seem to have anything to do with the question, but it is correct.) Dec 25 comment Do raindrops spin as they fall? Raindrops are not actually "teardrop-shaped", and do not have a tapered tail. This is just a common myth. The actual shape of a falling raindrop is a slightly flattened sphere, not entirely unlike, say, a round bread roll. Dec 5 comment In terms of forces and kinematics, why does a projectile, thrown forwards, bounce forwards? Note that, if the ball is spinning fast enough when it hits the ground, it can bounce backwards. That's probably not the case you're asking about, but I just wanted to point out that the direction of the bounce depends on both the velocity and the rotation of the ball. You can't treat those as independent, unless you want to neglect friction completely. Nov 23 revised How can we see the moon while it's between the Earth and the Sun? inline diagram Nov 23 answered How can we see the moon while it's between the Earth and the Sun? Nov 19 comment Could we launch a missile from a planet with the mass of Jupiter? Note that a planet with the radius of Earth and the mass of Jupiter would have a mean density of $1.7 \times 10^6\,{\rm kg/m^3}$. That's over 75 times the density of solid osmium, making such a planet pretty much physically impossible. (White dwarfs and neutron stars achieve far higher densities, around $10^9\,{\rm kg/m^3}$ and above, but there doesn't seem to be any way to have a planetary-size body with a density like your calculations imply.) A (slightly) more reasonable scenario might be a Jupiter-mass planet with the same density as Earth. Nov 17 comment Why can't I see the blue color scattered by the lower atmosphere of the earth? You sure you can't? You may just need to be in the right place (clear dry air + distant backdrop = mountains, typically) to notice it clearly.