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If a fly were hovering in a moving car just behind the windscreen (Windshield in the US), and the driver of the car were to brake sharply, would the flys inertia cause it to hit the windscreen, or would it remain in its original position? and why?
My old chemisty teacher asked me this question years ago and its bothered me since
- Doug (age 24)
The fly might well hit the windshield (windscreen UK) due to its
inertia. The only reason it might not is that flies have a lot of
friction with the air. Since the air will not be rushing through the
windshield, that friction will impede the fly's motion toward the
glass. However, if it started close to the glass, it will indeed hit.
Flies are heavier than air and so this argument is exactly right.
If you held a helium balloon in a similar situation, the heavier air
will by its inertia be pressed against the windscreen, and a bouyant
force will push the helium balloon backwards in the car.
(republished on 07/11/06)
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