Mike Dunlavey
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 Jan 4 comment How Vision Works Good place to start. Jan 2 comment Why does moving air have low pressure? Here it's more explicit. The air being deflected downward is not just the air below the wing, but also the air above the wing. In particular, anything that disturbs the flow on top of the wing, like a thin layer of frost, kills lift badly. Big cause of accidents. Also this. Note emphasis on top of the wing. Jan 2 comment Why does moving air have low pressure? Ummm... Last sentence? Try reading this. Dec 31 comment Driving on the moon ++ Yes. But if your runway took the form of a helical loop which then exited upward, you could do it :) Dec 18 comment Equal transit fallacy in viscous materials @Bob: Here's a very good and easily understood explanation. Essentially the flow is a summation of linear and circular motion (a vortex) resulting in the downwash. If the molecules rejoin there is no vortex. No vortex = no downwash, and no downwash = no lift. Dec 17 comment Remove measured distribution from another distribution Good question. You might want to ask it on Cross Validated. Dec 16 comment Aircraft lift theory vs energy conservation Drag is a function mainly of speed and angle of attack, and other variables. I can't recommend a better source of information than this. Also, the 747 is very efficient aerodynamically, as are all jet transports. This can be seen in their glide ratio, the angle of their descent under no power. A typical glide ratio for a jet transport is around 25:1, while for a Cessna 172 it is only around 9:1, in a clean configuration. If landing gear, flaps, or spoilers are out, it is a lot less. Dec 16 comment How is momentum conserved when is is only dependent on mass and velocity, and so many other factors come into play? @AdamGraehling: You're talking about momentum, not energy, so forget about heat and deformation. Those are conservation of energy, not conservation of momentum. In your example, when you say "no external forces act", that means no friction, like if the cars are on a greased surface. If so, the cars will not stop after colliding - the pileup will continue moving at the same speed as their center of mass did before. Dec 15 comment Why current loses its energy? Google electrical resistance. Dec 14 comment What makes bathroom soap bars to crack during winter season? @nemu: Just guessing - put a bar of soap in a cool oven? Travel to the nearest dry lake or river bed? Dec 13 comment why is pressure more convenient than force while dealing with fluids? These questions are very elementary. You want a general understanding of fluid statics. Think of a cube of fluid as full of bouncing rubber balls, and the walls are vibrating too (with temperature). That model answers all your questions. Dec 12 comment How does gas spin the turbine in a jet engine? @Ethan: Do you have trouble understanding how a table fan works, or a propeller on a boat? Failing that, does a paddle on a canoe make sense to you? Dec 10 comment If quantum tunneling is possible, is there a maximum thickness of material a particle can go through, and is it random? + I like your explanation but I don't see something that helped me understand it. Before entering the potential barrier the wave function takes the form $e^{-ix}$ so it is cyclical, but in the barrier the exponent becomes real $e^{-x}$ so it is an exponential decay (or something like that - I'm rusty on this). Dec 7 comment Fluid Dynamics - How does air behave out a window? If air comes in, some other air has to go out, or vice versa. It's not just one-way. (And quit smoking!) Dec 2 comment Lift provided to an aeroplane Aviation is over a century old, and it is very well understood. In spite of that, it's amazing how many people have been taught things that are wrong. Bernoulli's principle is not in conflict with Newton, in fact it is derived from conservation of momentum. Take a look at aerobatic planes with symmetric airfoils. They can fly inverted as easily as upright. The crucial variable is the angle of attack, which creates the downwash circulation. Asymmetric airfoils are nothing more than an optimization for non-aerobatic flight. Dec 2 comment How to calculate the time it takes water to travel 100' It sounds like the examiner is trying to see if you are confused by things that don't matter. I used to do that too. It's a good way to tell if you understand. Dec 2 comment How much effect does wind have on cooling an object? And various small airplane engines. Dec 1 comment What forces are applied as a car exits a curve with constant speed? +1 I would only add that in a car it takes a certain amount of time to move the steering wheel when transitioning from straight line to circular arc and back. In that time, the car is actually traveling in a spiral, so modern highways and railways all have spiral segments leading into and out of curves. (I programmed those on a 360 model 40!) Nov 30 comment Kinetic energy of fluid + collision @Tonylb1: Suppose have a stack of two 1kg boxes piled up. You grab the bottom box and lift the stack. How much force does it take? 2kg, right? Did the top box touch your hand? No. You lifted it through the bottom box. Gasses are the same way. Molecule A bounces off the surface. Then it bounces off B, then back, etc. Check out Newton's cradle. Nov 30 comment Why on a frictionless incline, a rolling object reaches the bottom slower than an non-rolling object? @Doeser: Smooth is one thing. Frictionless is another. If the slope is covered with grease, you won't get much rotation, it will all be sliding. Maybe you need to decide what your question is.