Jar of Flies

jar-of-fliesA scientist weighs a jar of sleeping flies. Then, he shakes the jar to wake them up. While flies are flying in a closed jar, the scientist weighs the jar again. Does the jar weigh less when the flies are flying?

Answer.

A fly is flying by pushing air downward. The fly applies a downward force on the air equal in magnitude to its weight mg. According to Newton’s 3rd Law, the air exerts equal and opposite force on the fly. Therefore, the fly stays in the air.

Now, the force is exerted on the air in the closed jar transferred to the walls of the jar. And finally, the force mg, the weight of the fly, transferred to the scales.

In conclusion, the jar weighs the same when the flies are flying.

Image By Blake Facey

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s