A coworker and I have an ongoing conversation about the following questions. Neither of us really know the answer, but we’ve developed many a wild conjecture. Without further ado, here they are:
Suppose you had a perfectly sealed box (the size doesn’t matter too much, but let’s say 10 feet cubed) with normal earth atmosphere inside it. Underneath it is a scale to measure the weight. Inside the box is a bird. If the bird starts flapping his wings and achieves liftoff, what would the effect be on the scale reading? Imagine bird takes off, flaps around a bit, lands and repeats.
Second question, same box. Instead of a bird, you have a 100 pound weight attached to the roof of the box (on the inside) and a nice fluffy pillow on the floor of the box. The weight has a release mechanism operated by remote control. Flipping a switch releases the weight and lets it fall to the pillow. Again, what would the scale show during the process of letting it hang, releasing it, watching it fall and then come to rest on the pillow.
Number three: Same box. This time, there is a fan affixed to the center of the box. The fan can be switched on and off by remote control. It is affixed such that it blows air towards the floor. Again, how would this affect the scale reading? (This ones a bit easy, but it helps set up the next one.)
Same box, also with a fan. But this fan is part of a “hovercraft” type device. It sits flat on the floor until the remote switch is thrown. Then it blows air enough to levitate a bit off the floor and drive around. Then the switch goes off and it comes to rest. For the last time, what would happen on the scale?
Okay, that’s pretty much it. It would be much appreciated if you labelled your responses complete guesses (that you aren’t really sure of) or as reasoned theories (that you think all the math works out on) or as answers (because people have asked and tested and answered these questions before). Or something like that.