how close can we get to the true weight?

Question

This is not my original idea, but this question has been bothering me for quet some time. The story goes like this: You take a fly and put it in a glass jar, and close the lid tight, you put the jar on a very accurate weight scale. If the fly is in motion (flying in the air and not sitting) at an instant moment when you measure the weight, will the jar be will this jar be heavier, lighter or the same weight as the same jar without the fly in it?

Answer 1

Buy eating properly all you like, doing exercises and forgetting about those crazy diets that can bury you.

Answer 2

If its not sitting on the jar, the jar would be lighter because the fly is not putting its weight down. But you would not be just weighing the jar and the fly, you would be weighing the air in the jar as well (i think, if that makes any sense).