HallsofIvy said:Do you mean "relative"?
HallsofIvy said:Yes, a fly does move "relative" to you but that doesn't mean it is going "at higher speed with no more effort". [...]
You might get a more interesting result if you calculate the flies kinetic energy using each of those speeds. Where did that enormous change in kinetic energy come from?
(Remember that kinetic energy is also always measured relative to something. Energy itself has no physical significance. Energy difference[\b] has physical significance
What I mean is, will the fly get more exhausted keeping up with the boat, even though the windshield bounce off all the wind? If not, why?
Ok, how come? Is the fly some how gaining the boats kinetic energy?Jelfish said:... For your fly and boat example, it may be that the windshield reduces the wind near the person enough that the fly can still follow the person's head without feeling like it has to compensate for the entirety of the speed of the boat ...
However much wind the fly feels is how fast he has to go to keep up with you. If you're talking about dragonflies, they will fly alongside boats, in the airstream, at up to 40mph. But any insect can fly along with you if they are not in the airstream.Lars Laborious said:What I mean is, will the fly get more exhausted keeping up with the boat, even though the windshield bounce off all the wind? If not, why?
If the fly is behind the windshield, the boat pulls a bubble of air behind it and the fly is pulled along with the bubble of air.Ok, how come? Is the fly some how gaining the boats kinetic energy?
Oh no. Perhaps I was assuming a bit too much. The fly's kinetic energy and the boat's are seperate. My explanation was assuming that the fly was buzzing around the person as though the boat were at rest. If the fly had no desire to stay in the boat, the wind shield wouldn't be enough to keep the fly in the boat (though that really depends on how large the wind shield is, how the fly is flying around, and the fluid mechanics of the system). The fly would only tag along if it were inside an enclosed space, where it wouldn't feel the effect of the boat moving away from the fly's air space.Lars Laborious said:Ok, how come? Is the fly some how gaining the boats kinetic energy?