Ross Millikan
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 18h comment While deriving Coulomb's Law from Gauss' Law, the power of 'r' comes out to be exactly 2 while experiment shows that it differs about 10^(-16). Why? You should provide a link to the data that you are citing. Is this within the error bounds? One would expect it to be so. 1d answered How precise can current technologies measure the mass of an object? Apr 23 awarded Yearling Apr 14 comment What role does the center of mass play in this situation? (electric potential) @NowIGetToLearnWhatAHeadIs: the figure has two pairs of masses linked by strings, so I think it is after the strings are cut. Then it says the two bottom ones are charged, but they still have a string connecting them. That is the source of my suggestion that the leftmost two are charged, presuming the string connecting them has just been cut, as has the one on the right. Apr 14 answered What role does the center of mass play in this situation? (electric potential) Apr 12 reviewed Approve Should I see evidence of neutron induced gammas on a background spectrum? Apr 10 answered A person on a concrete slab on a frozen lake starts walking $2 m/s$, what is the speed of the concrete slab? Mar 28 answered Helium Lift Potential Mar 26 comment Modelling an Airplane Question The density of air is usually considered to be constant. Where I have seen drag calculations, the velocity is the current velocity, not the terminal velocity. You can keep the state as a three position matrix, location, velocity, and acceleration. Then you update each one every timestep based on your acceleration and drag equations. Mar 26 answered How does quadcopter's battery capacity relate to it's maximum flight time? Mar 26 comment How does quadcopter's battery capacity relate to it's maximum flight time? I strongly disagree with the close vote. This is quite on topic. We want to encourage people to think about physics, which is what is being done here. Mar 20 comment How much more “work” (or energy) is required for short people to hike uphill? The physics answer is that the taller person needs a factor $\frac {40}{110}$ more energy to get up the hill. It seems reasonable that the efficiency of converting food to mechanical work should not be too different depending on height. The shorter person will need more steps, but each step will represent less energy output, so shorter legs are no disadvantage in this regard. Mar 18 comment How much more “work” (or energy) is required for short people to hike uphill? @JBentley: It is important to think about a question and what you are interested in. Mar 18 answered How much more “work” (or energy) is required for short people to hike uphill? Mar 15 comment Elastic collisions and 90 degrees angles In what reference frame? In the CM frame two objects are always moving in opposite directions. They can change direction by $90^\circ$ in inelastic collisions. It would not be convention, it would be because you can't balance momentum without balancing energy. Please draw a figure to show the angle you are referring to. Mar 13 comment Pumping water vapor into liquid water The usual way to make pure water vapor is to boil water. That gives water vapor at 1 atm pressure and 100C temperature. If you bubble that through room temperature water, the heat will go into the liquid water and much of the water vapor will condense as the vapor pressure of water at room temperature is much lower than 1 atm. When you see bubbles going through water, say in a fish tank, they are mostly air with (maybe) an equilibrium concentration of water vapor. Mar 13 answered Pumping water vapor into liquid water Mar 11 comment Maximize time of flight and range at the same time in projectile motion I don't think that question makes sense because $k$ is dimensional. The intuitive thing would be to take $k=1$ as giving them equal importance. If I measure T in seconds and R in mm, I get a very different answer than if I measure T in microseconds and R in km. If you set $k'=1$ you get $\theta = \arctan \frac 1{\sqrt 7}\approx 0.361367$ Mar 9 comment How the flow is distributed when the water flow from one river/drain to multiple rivers/drains? If you are given the total flow $Q$, as I said before you have $\Delta P=(\frac Q{\sum C_i})^2$ Then you plug that in to get $Q_i=C_i\sqrt{\Delta P}$ The flows divide proportional to the $C_i$ if all the $\Delta P$s are the same. It could be that the drains flow out at different elevations, so the $\Delta P$s are not all the same, but you can still find the proper $P$ at the junction to make the flow correct. It will probably take numeric solution then. Mar 9 comment How the flow is distributed when the water flow from one river/drain to multiple rivers/drains? I don't know how to use the information you have in point 1 to compute the $C_v$s. Maybe somebody has some software that does that. There should be tables available online for simple shapes, like round pipes.