| From: miguel | 23/06/99
17:58:16 |
| Subject: the fly | post id:
19342 |
| I would like to know
why? picture this... you are driving your car A fly is along for the ride (in the car) when you drive off - no matter how fast it doesnt hit the back window, however... if that same fly is at your side window (outside) when you drive off it only watches you depart in the distance.... hmmmmmmm | |
| From: legolas | 23/06/99
18:01:17 |
| Subject: re: the fly | post id:
19343 |
| I think it doesn't matter how
fast you go, the speed within the car does not change. The air
particle things aren't moving around or
anything. | |
| From: miguel | 23/06/99
18:05:11 |
| Subject: re: the fly | post id:
19347 |
| but if the fly is flying and the
windows are open he or she still doesnt hit the rear window.. i like your thoughts though | |
| From: Daryn Voss | 23/06/99
18:19:48 |
| Subject: re: the fly | post id:
19356 |
| In the following discussion, all
references to velocity will mean velocity relative to the road. Let us say that there are two things that will affect the velocity of the fly; 1) Va, the velocity of the air that surrounds the fly and 2) Vr, the fly's velocity relative this air. (I'm assuming this is all happening in a straight line.) The latter will be determined by the fly's behaviour. So V = Vr + Va. Suppose I am driving along at 20km/h and there is a fly somewhere outside my car, zooming along at 20km/h in the same direction. Let us also ignore turbulence and wind, so that we may say that Va=0km/h and Vr=20km/hair, so V=20km/h. Now, let us say that this fly is content to maintain this speed (it isn't trying to keep up with us). We accelerate, but the fly's relative speed doesn't change, the air speed doesn't change, so V still equals 20km/h, and the fly tastes our dust. Suppose instead that the fly is in the car. Va in the car is 20km/h, the same as the speed of the car. The fly is also moving at the same speed as the car, but Vr=0km/h. Relative to the air it is in, it is just hovering. We apply acceleration, Va also increases, but Vr stays at zero. So the fly stays at whatever speed the car is doing, and doesn't smack the back window. 8^) | |
| From: mike | 23/06/99
22:46:33 |
| Subject: re: the fly | post id:
19420 |
| Miguel there is also another thing to consider in this question When you apply a force to the car and accelerate away you will also apply a force to the air inside the car via 1)the back window creating a higher presure on the air 2)the front windscreen creating a lower presure on the air. As your fly is hovering in this air it is producing a force equal and oposite to it's mass therefore giving it the appearace of maitaining a stable position.As this air moves with the car your intrepid fly gets forced to go with the flow ,tha is it moves with the air in the car because this air is applying a force to the fly (in actual fact it will move to the back of the car a small amount). NOW TO SHOW THIS here is a small exsperament that you can do to show this Materials: 3 balloons 1 broom handle (wide enough to go across the back seat of the car) some water some balloon gas He(or any gas that will make the balloon float) some string Method: 1-Fill one balloon with He,one with water,one with a mix of air and He(it should not float or sink). 2-tie these to the pole and fix it to the rear doors so that the balloons are free to move around without hitting anythingg. 3-get a mate to hammer it as if he's on the strip up against Victor Bray while you watch the balloons Conclusion: now that you have done the physial tests you need to answer why to do this you need some mates some beer and time to ponder Have fun with this regards mike | |