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 Jan 23 awarded Yearling Sep 24 awarded Autobiographer Jan 14 awarded Yearling Nov 23 comment Tension in vertical circular motion What makes you say that tension isn't conservative? Sep 12 awarded Critic Feb 6 answered If we are travelling with the speed of light, can we see what's behind us? Jan 25 comment Does light induce an electric current in a conductor? You neglected to mention that if the energy of the photon must be higher than the work function of the metal, excess energy may be carried away by the ejected electron by the photoelectric effect. Jan 24 comment Ways to create controlled small bubbles in water within plastic tubing This isn't an answer, but I had some friends in grad school who worked with the physics of bubbles. They always used nitrous oxide. I'm not sure why, but they did say, vaguely, that it made for better bubbles. Jan 24 comment Does the Earth rotate the same encased in ice during the height of an Ice Age as it does when the bulk of it's water is liquid and always in motion? The tides will change, too. With less water to slosh around, the earth will transfer rotational energy to the moon more slowly. The moon's rate of outspiraling from the earth, and the rate of slowdown of the day, will probably decrease modestly. Jan 22 comment Rotating a reference system on a vector Ouch! Yeah, been there, back when I was learning this stuff. Jan 22 answered Rotating a reference system on a vector Jan 22 comment Rotating a reference system on a vector I'm not sure you're correct. The inverse should map (0, 0, 1) to his original vector; it maps it to x⃗ =(-sin(ϑ)cos(φ),sin(ϑ)sin(φ),cos(ϑ)) (note the minus sine in the $\textbf {i}$ direction) Jan 22 comment Is there any case in classical mechanics where Newton's (strong) third law doesn't hold? @SumukhAtreya Ah, yes, I was right in my guess. The weak form simply implies conservation of linear momentum, the strong form conservation of angular momentum. And for conservative, spherically symmetric fields centered on the point particles, you're right. You can't have a torque between two point particles if they can only push & pull each other along the line. Let them "shove" each other "sideways" (by which I mean perpendicular to the line joining them), and you still have an action/reaction pair, but it violates conservation of angular momentum. Jan 21 comment Is there any case in classical mechanics where Newton's (strong) third law doesn't hold? oops, used p rather than r, sorry. I was learning the LaTex to make it look good, and went over the 5 minute deadline for re-editing. For $\textbf{p}$, please pretend it's $\textbf{r}$ Jan 21 comment Is there any case in classical mechanics where Newton's (strong) third law doesn't hold? Okay, I had never seen "weak" form applied to Newton's 3rd Law, and a quick googling doesn't give me the answer in the top 2 hits, but I assume you mean the case where the net force is zero, but the net torque is not. For example, suppose we have a 2-dimensional system, with particles at positions $\textbf{p}_1=1m \textbf{i}$ and $\textbf{p}_2=-1m \textbf{i}$, but forces $\textbf{F}_1=1N \textbf{j}$ and $\textbf{F}_2=-1N \textbf{j}$. This isn't made explicit, but it's not seen in nature. If seen, it would violate conservation of angular momentum. Jan 21 comment How are current and voltage out of phase in capacitive circuit? @Qmechanic Looks the same to me, but I feel like the answer wasn't very good. What's the protocol -- answer the older question, or the newer one? Jan 21 comment Is it feasible to detect light emitted from planet earth 2,000 years ago by reflection from an object situated 1000 light years away? We'd want to calculate the number of photons that are incident & then reflected from the earth (from the sun, the brightest source in our vicinity), then assume a $\frac{1}{r^2}$ law to see how many of those reflected photons hit the distant planet, then determine what fraction of those photons are reflected from the distant planet, give it another $\frac{1}{r^2}$ law on the way back, and see how many photons get back to us. I'm guessing it's <<1 per year, but haven't done the math. At that rate, it's going to be hard to separate that expected photon each year from noise. Jan 21 answered Is there any case in classical mechanics where Newton's (strong) third law doesn't hold? Jan 19 answered Could one argue that h (Planck constant) and $\hbar$/2 (Dirac constant) are in fact independant constants? Jan 18 comment Calculating projectile range from known maximum height and time traveled Don't factor in wind resistance; it gets annoying. As for hang time, you should already know how to calculate hang time for a drop from a certain height. The real question is, did you calculate $v_{0x}$? With that & the time, you can see how far it goes.