# Total newb question

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Hello all. I would appreciate any help anyone is willing to give me. I think I'm posting this to the right discussion board. I apologize if not.

This may be a bit of a silly question but here goes...

I was driving in a van with my family when I was young. We're going about 60 miles an hour down the interstate. While we were driving, a fly was flying back and forth through the van.

Now, I know the fly was not going 60 miles an hour while flying from the rear of the car to the front of the car. I never understood why the fly was not stuck to the back window.

What scientific principals or theories might be involved that could explain how the little fly could go from the back of the van to the front of the van while we were traveling 60 miles an hour?

It's like the van was its own little world for the fly to move around in, while the van was moving its its own world, at 60 mph down the road.

Silly, know. But it has always puzzled me.

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10 minutes ago, kjp said:

It's like the van was its own little world for the fly to move around in, while the van was moving its its own world, at 60 mph down the road.

Silly, know. But it has always puzzled me.

The van can indeed be considered as the fly's own little world, as with all the contents of the van.

The fly starts off on some interior surface of the van and is accelerated, like everything else, to 60mph.

So when it jumps off to fly back or forwards, it is alredy going at 60 mph and it only has to generate its normal flying speed to reach the other end.

Since the air inside the van is also going at 60 mph it offers no more than normal resistance to the fly.

Does this help  ?

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Imagine trying again, with the front and back windows removed from the van.

(As this was posted in the "relativity" section, kjp, is your next step to compare the fly with the photon of a light clock?)

Edited by pzkpfw
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6 hours ago, kjp said:

It's like the van was its own little world for the fly to move around in, while the van was moving its its own world, at 60 mph down the road.

You have probably been in buses and airplanes, able to move from one part of the vehicle to another, without once getting plastered to the rear wall. You are moving at the same speed and direction as the vehicle, relative to the ground, but a different speed and direction relative to the interior of the vehicle.

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All motion is relative to some fixed point.  You van is traveling at 60 mph relative to the road.  The fly is traveling at some much lower speed relative to the van.  It speed relative to the road is very close to 60 mph (slightly more when it is flying forward, slightly less when it is flying back) but since it is flying in the enclosed air in the vehicle the fly doesn't notice it.  (If the car were to accelerate the fly might wind up plastered to the back window- acceleration is not relative.)

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1 hour ago, Country Boy said:

All motion is relative to some fixed point.

That makes you the fixed point, not some relative...

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22 minutes ago, dimreepr said:

That makes you the fixed point, not some relative...

The notion of 'fixed point' is abitrary.

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Just now, StringJunky said:

The notion of 'fixed point' is abitrary.

Indeed...

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