- Jar Of Flies - Explained!


Jar of FliesCongratulations to all of you who were able to order their free dinosaur skeleton kit last week.

We are really proud of you. 67% of all students who participated in the quiz selected the correct answer.

Frank Cascarano, Physics Instructor at the Foothill College, CA was so kind to explain the physics occurring inside the jar.

Here is the question again for those who don't remember: Maxi and I had a little disagreement over the weight of flies in a jar.
You place the jar on a scale. The scale will register the most weight when the flies are
a) sitting on the bottom of the jar
b) flying around inside the jar
c) ... the weight of the jar is the same in both cases

Click here to watch Frank's explanation on our Youtube Channel or continue reading his explanation.

"Short answer is: it weighs the same whether the fly is hovering in the
middle of the jar or landed on the floor of the jar. Basically, when you weigh the jar you are weighing the jar and all of its contents. Another example, if the jar has air in it, the jar will weigh more than a jar that has been evacuated and just contains a vacuum.

Long answer is that it does depend slightly on whether the fly is moving (well, actually, whether the fly is accelerating). With the fly in the air the jar could weigh more or less than with the fly standing on the floor of the jar, depending on whether the fly begins moving up or down. Let's just say the average weight of the jar+air+fly when the fly is flying is the same as the weight with the fly on the floor of the jar."

We also liked deborah109's answer a lot! Thanks for your excellent explanation!

"Since the jar is closed when it is weighed all of its contents are being weighed. (jar, lid, air, and flies no matter the positin of the flies.) The flies in motion would still put pressure on the air then the jar then the scale."
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