Plane on conveyer: Will it ever take off?
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From: Seattle, WA
I didn't say that though, did I? I said sometimes that is the case. Again, in *general* colder water freezes faster than hotter. BUT - there are times when the *same* volume of hotter water will freeze faster than colder water.
It doesn't work the other way though, hotter water always boils faster than colder water.
It doesn't work the other way though, hotter water always boils faster than colder water.
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From: Ohio
Originally Posted by Tedow,Dec 2 2005, 12:36 PM
That's the argument most people try to make I think, but it's wrong. Here's why: the rolling friction of the wheels against the ground is constant regardless of the speed at which the wheel is rolling. Friction force = friction coefficient * normal force, where the friction coefficient is one of two values, "static" or "dynamic." The static value is higher...friction coefficient decreases once the object starts moving (that's why it's easier to keep a heavy object moving than it is to get it started in the first place). The normal force, at its maximum, is just the weight of the aircraft...it will start going down when lift is generated, but ignore that for now. So what you have is a constant times a constant...once the object (wheel) starts moving, the friction force it exerts against the ground is constant no matter what speed it's moving at. There might be some minor variations when you throw in stuff like heating or tire deformation or something, but essentially it stays constant. The thrust of the engine is fighting the aerodynamic drag of the airframe and the rolling drag of the wheels. Obviously, the thrust must be greater than the drag, or planes would never be able to take off at all. Also, since the rolling friction is independent of speed, that value stays very small all the time (or else, again, planes would never be able to take off). Hence, the presence of the conveyor belt does nothing to prevent the plane from accelerating and taking off.
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From: Minneapolis, MN
The trick is acceleration. The question is intended to make you think that the plane is being held in place while the belt turns the wheels.
i.e. wires holding the plane in place = no lift
thrust allowing for acceleration = lift
i.e. wires holding the plane in place = no lift
thrust allowing for acceleration = lift
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From: San Diego, CA
Originally Posted by exceltoexcel,Dec 4 2005, 12:03 PM
I googled the boiling/cold water thing. There are several experiments that show, cold water from the average tap boils faster than hot water from the tap, but I have found many sites that dispute this. Also many experiments that show boiling water freezes faster than normal cold tap water, and the majority say this is true.
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From: limerick
Originally Posted by PeaceLove&S2K,Dec 4 2005, 08:08 PM
Maybe the hot water pipes in question are dirty, causing contaminants to get dissolved in the water, thus raising the boiling point of the water.
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From: limerick
an experiment you can do on your own, if its freezing outside.
http://hepth.hanyang.ac.kr/~sjs/physics/hot_water.html
http://hepth.hanyang.ac.kr/~sjs/physics/hot_water.html
