Re: Bird flyng inside a moving vehicle

First of all, velocity is relative.  That is velocity must be measured 
between two things.  There is no "absolute" velocity.

When a bird flies, it flies through the air.  It generates lift, thrust and 
drag all through interaction with the air around it.  As far as its 
aerodynamics are concerned the only important thing is the speed of the air 
over its wings, body and tail.

Now when a bird flies inside a moving car, the air within the car is moving 
 with the car, and with the car's speed relative to the earth outside.  
However the important thing to the flying of a bird is the speed of the air 
over its wings.  So the bird needs to fly through the air of the car just 
as it would fly through the stationary air outside the car.

To an observer outside the car the bird is flying relative to them at the 
speed of a bird plus the speed of the car.  To an observer in the car the 
bird is flying at the speed of a bird.

The same thing happens for birds and aeroplanes in wind.  Their speed 
relative to the ground changes depending on the wind, but their speed in 
the air remains the same.  Similarly for boats in currents etc etc.

I am not sure what your hover question was about.  Do you mean it would 
hover in the car, relative to people in the car?  The only way it could do 
this if it was a bird that can hover in still air (like a humming bird).  
As far as the bird and the people in the car are concerned there is no 
difference to flying in a car as there is to flying in still air outside 
the car.  Steady motion of the car (no accelleration) does not change the 
way the bird flies relative to the car.

If the windows of the car where blacked out, and it moved at a constant 
pace you could not in fact tell if the car was moving or stationary.  A 
bird would fly around merrily, unable to notice the movement of the car, 
whether it was doing zero relative to the earth or if it was doing 99% the 
speed of light relative to the earth.

Martin Smith