# Speed of a fly inside a car

A couple of weeks ago I was travelling in a car (120 km/h approximately) and I saw a fly flying in front of me (inside the car, near my nose, windows closed). I wonder how was that possible.

Does it mean is really flying at 120 km/h or the fly is being affected by some kind of gravity/force?

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Outside the car? How far in front of you was it? –  David Z Jan 31 '12 at 23:46
Sorry, I updated my question –  César Jan 31 '12 at 23:50
It flies 120 km/h if it was a convertible without windshield. Did you feel like you where in a hurricane in your car? If not then why should the fly? –  Alexander Feb 1 '12 at 0:00
Because the fly can fly. I can't –  César Feb 1 '12 at 0:06
But in a 120 km/h wind your are pretty close. It is really not more subtle than this, the wind you feel on your nose is the same wind the fly feels, so in a closed car almost nothing. The fly does not have to be strong at all, it also works with dust in your car, it will stay more or less in one place as you move the whole air inside your car around with you which acts like a 'seat' for the fly. –  Alexander Feb 1 '12 at 0:16

So the speed of fly with respect to you is $v=0\,\frac{m}{s}$, with respect to some observer on the road is $120\,$km/h.