Question

If a humming bird flew into a running car and was still off the ground while inside, would it need to fly at the speed of the car, or float as if the car were not moving? Why? Does having the windows open/ closed change anything (assuming the bird is already inside)?

Answer 1

A hummingbird, or any bird, flies by pushing air downwards. And it pushes air back to move forward with the respect of a zone of stationary air, not the ground. Air pushes the bird forward not the ground.

A car usually has still and stationary zone of air inside. Unless the front windshield is broken (of course no) or the roof is open, the air inside does not have a velocity equal to the car's velocity. Opening a window makes the air inside turbulent but not that high-speed.

When the hummingbird enters the car two things happen:

a) While it's entering the car outside air has a backward velocity = car's velocity and it has to push air quickly to match up with the car's speed and enter inside. Respect to the ground the bird has a velocity = car's velocity.

b) As soon as it enters into the car, the bird experiences a stationary block of air, all the windows are closed. The bird no longer has to fly forward, it just has to stay afloat by thrusting air downwards. So, the bird flies as if the car was not moving. Although with the respect to ground the bird moves = speed of the car.

If a window is open and the bird is flying close to any of the windows while it's in the car, air flows in with a speed = car's speed and it pushed the bird backwards. So just floating no longer works, it then has to move forward to catch up and not fall behind.

However, if the car s big and only a small number of windows are opened, the air becomes a little turbulent and the bird will have to stabilize its flight in all direction.