Not sure why, but anytime I see a bug sitting on my car's exterior, I make it a game to see what it takes to throw it off. My driving gets progressively faster (or reckless, as the case may be -lol), until I finally ditch the bug.

Today I noticed a fly on my side view mirror (driver's side). I was in an urban area, but I managed to get a constant speed of 40mph going. Since the fly was literally on the mirror it was shielded from the wind and there was no way air speed was going to cause it to lose hold without some nasty turns. So I cracked the driver's side window to see if that might do something to the air flow. As I expected, it did nothing.

Then I cracked the passenger side window and the fly immediately was thrown off! What was it about cracking the passenger window that disrupted the air flow on the driver's side mirror? A diagram of air flow would be great, but I don't expect anyone to go through the trouble. So a simple explanation would suffice. Thanks.

Btw- I'm 90% sure this wasn't just a coincidence and the fly just decided to take off at the exact moment I cracked the window. There definitely seemed to be a correlation between cracking the window and the fly. The result was immediate. I'm not even 100% sure the fly was alive.

Maybe the fly bailed when he noticed you were swerving through city streets going 40mph whilst staring at your rearview.

Maybe you were on the side view mirror and the fly was driving.

Both windows down no? Seems like an easy answer if that is the case.

No. Sorry. All windows were up! Could it have been an air pressure thing? Or was it air flow?

LOLZ at the other two responses so far. But this is a serious question.. I'd really like to know how opening one window effected the other side of the car.

2 lulz in a row in two threads. Are you following me for comic fodder? I litlerally lol'd at this one tho.

Did you notice the pedestrian on your windscreen?

I'm 100% sure you have no way of knowing this.

PS I can simulate this for you for only $200/hour.

Two questions.

When you cracked the passenger side window and the fly left, was the driver's side still cracked or had you rolled it back up?

Is there a mirror on the passenger side?

No. All windows were closed. I cracked the driver's side and nothing. I closed it. Then I cracked the passenger side and the flop was immediately blown off.

Is there a mirror on the passenger side?[/QUOTE]

Yes.

I'm very sure the fly was blown off from the window opening, Obviously, I can't prove that so I'm not going to argue with you.

I appreciate having fun with this, but I thought it was an interesting and serious question.

You are looking in the wrong area, this has nothing to do with aerodynamics. It's all about the fly's mirror neurons.

OK. I might have been able to concoct something remotely plausible if your driver's side window was open and there was an assymmetry in the airflow over the car due to a missing passenger side mirror. I am not sure I would have believed it. Without that, I have nothing. I think it was coincidence.

If you are really curious, take some tape and a few strips of Kleenex and tape them to the driver side mirror. Drive at 40, (if that was the speed) and move the windows as you did. If something profound is happening you should be able to see changes in how the strips of Kleenex move. Make them short. If they are so long that they get out of the stagnation zone created behind the mirror then the motion will be dominated by forces that you are not interested in.

Thanks RLK! It's certainly possible it was a coincidence, but I honestly don't think it was. I like your idea and I'm going to try it. If successful, I'm going to expect some apologies -lol. If it fails, it won't be the first time I made a fool of myself on here.

Cool. Let me know what happens. By the way, when I said I would not have believed it, I meant I would not really have believed the explanation I was concocting. It was not an expression of distrust about your fly story. I have no reason not to believe that you have reported what you observed.

Haha. No worries. I was talking about all the jokes, smart ass comments, and lack of serious answers left by most who responded. I guess they don't know the answer.

But (if the window did have something to do with it), I really thought this would be an interesting question for SMP. Aerodynamics can be interesting and also counter intuitive. When I was a kid and blew on the TOP of a piece of paper for the first time to see that it lifted from underneath (same principle that provides lift in a plane's wing), I was amazed.

Anyway, I'll report back ITT with what happens. Thanks again.

lol i know exactly what youre talking about. it WAS cracking the 2nd window that caused it. the aerodynamics involved are above me, but i can confirm this phenomenon. also curious as to the explanation.

Looks like it may have been a coincidence, although I'm STILL not totally convinced.

I tried RLK's experiment and cracking the passenger window didn't seem to have any effect. However, the Kleenex was constantly flapping even before the window(s) opened. Unfortunately, opening the window didn't seem to cause it to flap any more or less.

So I think I need to try something different. I'm just not sure what. Maybe cutting the Kleenex in a strip was the problem? I think I'll try balling it up and adhering it with a piece of tape on the bottom. I'll welcome any other idea (except taking a driver's safety course). Thanks.

I tried it this AM also with the same result. I had a very short piece taped to the mirror. It flapped around although not violently, but there was no change when I opened the windows. I am leaning towards coincidence also.

I'm not a math guy, but the fly was on my mirror for at least 3 minutes. Even if the fly taking off took a full second the chances would be 1 in 180, correct? And of course, it only took a fraction of a second. I'll try once more in a different way and then I'll then concede it was a coincidence.

Anyway, this is why science is so cool. Thing aren't always what they appear. Even observation can be misleading and cause a jump to the wrong conclusion.

That is true when assuming his/her/its departure is truly random. It seems to me that this is not the case. It then becomes considerably more difficult.

Also, that's assuming that the fly can only be on the window for 3 minutes maximum.

its not a coincidence. next time youre driving on the highway, go for a little while with just the driver window down. once youve calibrated that, open the passenger window. you will easily notice the difference in airflow.

edit: not saying that the airflow was necessarily responsible for any actions the fly may have taken, but 1 window vs 2 does make quite a difference in terms of the 'wind power' or whatever that is going through the car.

When you say that it seems to you this is not the case, do you agree that it likely had something to do with the passenger side window being opened?

If not, then what other possibility is there other than the random chance event that it just happened to have flown off at the exact moment the window was opened on coincidence?

Thanks. I do understand that 1 window vs 2 makes a difference. But only one window was open (starting with all windows closed, I first cracked the driver's side. Closed it. Then cracked the passenger side, which is when the fly appeared to be blown off).

Although... Now I'm wondering if I could be wrong. Maybe I didn't fully close the driver's window before opening the passenger side. I'll test for this also. Thanks again.