Physics Weekly Newsletter - Monday, July 28, 2014

Top new questions this week: Which ball touches the ground first? This is a very well known problem, but I can't find an answer in the specific case I'm looking for. Let's consider two balls : Ball 1 weighs 10 kg Ball 2 weighs 1 kg Balls have identical volumes … homework newtonian-mechanics newtonian-gravity drag free-fall   asked by FlipFlapFlop 25 votes answered by Bernhard 43 votes Why is the pressure inside a soap bubble higher than outside? Apparently, the air inside a soap bubble is under higher pressure than the surrounding air. This is for instance apparent in the sound bubbles make when they burst. Why is the pressure inside the … pressure air surface-tension   asked by David Zwicker 19 votes answered by David 32 votes Is this really a golden ratio spiral? In this blog post, I found this picture: Does the water really form golden ratio spiral in such cases? Or is the photo just a provocative example, without physics grounds for claims about … fluid-dynamics everyday-life   asked by VividD 14 votes answered by Phil Frost 13 votes Why do bubbles make a sound? I have an understanding of how bubbles work. They encapsulate air (or other fluids) in a membrane caused by surface tension. When they pop, there is often a sound. Sound is a type of energy, kinetic … everyday-life acoustics pressure air   asked by Thoth19 14 votes answered by David Zwicker 16 votes Pool in a submarine A common theme in aquatic science fiction is the submarine pool/access to the ocean. That terrible TV show Seaquest had it, The Deep & Deep Blue Sea (Samuel L Jackson is standing in front of it … pressure   asked by George R 14 votes answered by bowlofred 13 votes Is the frequency of light restricted? What are the factors that limit the frequency of light? Can it have wavelengths ranging between zero and infinity? electromagnetic-radiation visible-light frequency wavelength   asked by Afrish Khan 13 votes answered by LDC3 6 votes Is speed of light and sound rational or irrational in nature? Just as circumference of circle will remain $\pi$ for unit diameter, no matter what standard unit we take, are the speeds of light and sound irrational or rational in nature ? I'm talking about … speed-of-light mathematics physical-constants   asked by kaka 13 votes answered by David Z 45 votes Greatest hits from previous weeks: Why does the road look like it's wet on hot days? Often, I'll be driving down the road on a summer day, and as I look ahead toward the horizon, I notice that the road looks like there's a puddle of water on it, or that it was somehow wet. Of course, … optics atmosphere   asked by voithos 11 votes answered by Lagerbaer 19 votes Why do grapes in a microwave oven produce plasma? Some of you may know this experience (Grape + Microwave oven = Plasma video link): take a grape that you almost split in two parts, letting just a tiny piece of skin making a link between each … electricity electrostatics physical-chemistry home-experiment   asked by JBE 17 votes answered by John Rennie 9 votes Can you answer these? What's the corresponding symmetry of enstrophy conservation? In fluid mechanics, especially 2D turbulence study, people talk about conservation of enstrophy. But I can't really understand enstrophy very well, and what's the corresponding symmetry of enstrophy … fluid-dynamics symmetry conservation-laws turbulence vortex   asked by physixfan 3 votes Which cosmological dark matter theory is most compatible with current particle physics? This occurred to me while I was writing Why hasn't warm dark matter replaced cold dark matter as the standard model of cosmology? but I think this deserves a question of its own. The background … particle-physics cosmology dark-matter   asked by Kyle 3 votes Derivation of force law in special relativity I've seen force defined in special relativity as the rate of change of 4-momentum $$ {\bf{F}} = \frac{d {\bf{p}}}{dt} $$ Can anyone comment on the following derivation of that relation? Take one … special-relativity   asked by Melativity 3 votes

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