My Favorite Science Puzzles

None of the following puzzles have trick answers, or unwarranted assumptions, but they involve knowing some physics.

1. A barge with one man and a load of iron scrap is on a barge floating in a lock in the Panama Canal. If the man throws some iron off the barge into the water, what will happen to the water level on the side of the lock?

2. A van with all the windows closed contains some helium-filled balloons floating in it. When it starts accelerating what happens to the balloons?

3. A van containing pigeons on perches is being weighed on a scale. Something scares the pigeons and they all begin flying around inside the van. Does the total weight of the van and pigeons change?