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4h
comment Do gravitational waves travel faster than light?
It's good to be skeptical, both of positive results and negative results. It's worth deeply evaluating the arguments, pro and con. General suspicion is not very helpful.
4h
answered How can I calculate how high an arrow goes when all I know is its initial speed?
2d
revised Is it possible that a plane in turbulences has more downward acceleration than gravity's
added 517 characters in body
Feb
9
answered Why doesn't Torque of masses on a pulley depend on the friction between the rob and the pulley according to a question in the physics 1 book
Feb
9
comment Why does a propeller suck in air from the front?
@jameslarge: Yes of course there's a pressure difference. The wrong explanation is the one that says the air parcels reunite at the trailing edge - the "equal transit time" fallacy.
Feb
8
revised How can a product of Bra and Ket be a scalar if they are matrices?
added 67 characters in body
Feb
8
answered How can a product of Bra and Ket be a scalar if they are matrices?
Feb
8
revised Is it possible that a plane in turbulences has more downward acceleration than gravity's
added 119 characters in body
Feb
8
revised Is it possible that a plane in turbulences has more downward acceleration than gravity's
added 83 characters in body
Feb
8
revised Is it possible that a plane in turbulences has more downward acceleration than gravity's
added 266 characters in body
Feb
8
answered Is it possible that a plane in turbulences has more downward acceleration than gravity's
Feb
6
answered How can I clarify the difference between free falling and Newton's law?
Feb
5
comment 2 airplanes same size and shap different mass
Not steeper, just faster. Both lift and drag are proportional to velocity squared, so their ratio is roughly constant, L/D. The tangent of the descent angle is just D/L. So if Weight is greater, Lift must be greater, so Velocity increases as the square root of Lift, and Drag increases linearly with Lift. So - same angle. For a small plane, the L/D ratio is about 9. For a jet airliner it is more like 25. For a sailplane, 30.
Feb
4
comment Adding cinnamon to my coffee makes it stop whirling much faster: Why is thats?
@HolgerFiedler; I'm with you. I suspect the coffee below is still spinning.
Feb
4
comment What is the difference between vortexing and centrifuging?
+1 The difference is in the angular velocity as a function of radius. In a vortex the angular velocity decreases as $1/r$, while in a centrifuge it is constant, so in a centrifuge the centripetal acceleration $\omega^2r$ increases with radius, so things more rapidly float/sink to their preferred depth.
Feb
2
comment Why is an airplane propeller so different from a boat propeller in shape?
I'm not sure I believe that other answer. This is just a comment because I don't really know. I can only point out that they are both rotary wings, and the lift/drag ratio of a wing is better if it has higher aspect ratio - long and narrow. Another factor is cavitation - water propellers cannot have too large of a pressure difference, to minimize steam bubbles, so they might have to make up for it with area. But I don't really know.
Feb
2
comment If the Earth is curved, why don't planes need to adjust attitude to stay parallel to the ground?
@Dargscisyhp: So you should know what I mean, having had your hands on the controls yourself. Aircraft power is not on/off, if it more/less. Aircraft are always gliding. Whether they glide down or glide up is just a matter of whether the thrust is less than the drag or more. If you want the plane to maintain constant height above the earth, that's one power setting. If you want it to follow a "straight line" and ascend, that takes a higher power setting. If you want to descend to the airport, you decrease the power, to idle if necessary.
Feb
2
comment If the Earth is curved, why don't planes need to adjust attitude to stay parallel to the ground?
@DavidHammen: Yeah, sure. Good planes, properly loaded, damp that out. (I'm talking about common aircraft. Aerobatics and fighters are a different story.)
Feb
2
answered If the Earth is curved, why don't planes need to adjust attitude to stay parallel to the ground?
Jan
29
revised How do the Americas Cup Yachts sails work?
added 28 characters in body