Physics Brain Teaser: Bee in a Jar

Imagine you’ve got a jar on a scale, sealed so that no air can escape. Inside this jar, there’s a bee hovering in place. Does the scale read more, less, or the same as when the bee is resting at the bottom of the jar?

Image Credit: Elder Scrolls Wiki

At first blush, you might think that a hovering insect’s weight shouldn’t show up on the scale, but you’d be mistaken! If the jar is sealed and the bee stays at a constant height, it doesn’t matter whether the material propping it up is air or glass—it’s exerting the same amount of force on the scale. If you’ve ever been around a helicopter while it was taking off or landing, you might have felt a fraction of the rotors’ power as air was forced downward and then, having nowhere else to go, outward. The total force exerted on the ground by the helicopter must be equal to the helicopter’s weight in order to keep it aloft at a constant height, but since the force is transferred through air, it’s spread out. Since our bug is in a jar, however, and the jar is sealed, there’s no way for the air (and the downward push imparted onto that air by the bee’s wings) to disperse. As a result, the air molecules colliding with the bottom of the jar have more force than those colliding with the jar’s other surfaces, and it acts heavier—as though the bee were sitting still on one of the jar’s interior surfaces.

What would happen if the bee were to flap faster or slower, and rise or sink in altitude within the jar? Post your answers in the comments below!

You may also read these articles