Imagine a bird in a parked bus. The bird is at a standstill in midair (say it's a colibri ), it's speed by that being 0 km/h. The bird is thus not touching the interior of the bus. Now imagine the bus accelerating, only driving straight forward (no, it will not crash into anything). The question is as follows; will the bird hit the back window? The given factors above should be considered only (don't be a nitpicker I mean by that). Present your arguements!