An empty semi-truck sits on the scale of a weighing station. it is then loaded with 100 irritated pigeons. these two events then happen in sequence. a) first, the super irritated pigeons just stand on the floor of the truck. b) second, they take flight inside the truck. they all fly in the enclosed space such that they do not collide with each other or the walls/ceiling/floor. is the reading on the scale different in a) versus b)? does the reading on the scale change during the transition of these events?

The reading in the scale is going to be the same, or if it experiences some change it would be minimum. The reason is because the truck will act as a big closed cage, therefore, when the pigeons fly, the air they move with their wings in order to keep flying,  exerts the same force on the closed cage, that if they were standing on the ground.

If the truck however, allows the air flow, the weight might change, because under this scenario, the air flowing could represent less force exerted on the balance.

Explanation:

the duration of a photographic flash is related to an rc time constant, which is 0.100 μs for a certain camera.