If a fly is trapped inside a moving car does it have to fly as fast as the car is travelling?

• If a fly is trapped inside a car doing 80mph and the fly is flying around inside the car, is the fly flying 80+ mph just to keep off of the back glass?

• Answer:

  No. The key for how to think about your question relates to a thing called "relativity and frame of reference". For example, relative to an observer standing on the side walk watching the car go past, the fly is in fact moving at 80 MPH relative to that observer. But, relative to an observer's frame of reference while seated inside the car, the fly is just buzzing around at a few feet per second (very slow as compared to 80 MPH). And with regard to needing to move at 80 MPH to "stay off the back glass"... Since the predominant "frame of reference" is the car, and since the car is affected by effective 80 MPH wind resistance while the fly is not, the fly has no risk of being crushed against the back glass. Unless you get sick of the pest and smash him with a magazine.