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silverscorpion • Jan 22, 2009

# A silly little puzzle..

Hi all,
I have a weighing scale and there is an empty plastic bottle on the scale. A certain reading is shown in the scale. Now, a fly enters the mouth of the bottle. Note, it does not go to the bottom of the bottle. It's just flying inside the bottle. Is there a change in the weighing scale? Why?

P.S: [This qn is asked in a puzzle competition in our college. I have guessed the answer, but I dont know it for sure.]
m_rahuul • Jan 22, 2009
no!...there will be no change in the weighing scale....
the simple reason being that as long as the fly is just flying inside the bottle and has no contacts with the bottle....it does not exert any force on the bottle(no action-reaction exists).....and we know that weight is a form of force..no force=>no weight change
Kaustubh Katdare • Jan 22, 2009
Heh, I bet the answer is going to be 'yes'. But I'll go with a 'No'. At least, that's what I've observed 😉
shalini_goel14 • Jan 22, 2009
I guess it is going to affect the weight. 'Yes' beecause now weight of bottle will include the weight of that fly also. Isn't it?
The answer i think is yes ,but not due to the weight as it doesnt put weight on the bottle , but as its the small bottle as the fly flies the air around the bottle may excert some pressure on the bottle so the weight changes , this is my anticipation. 😛😛
raj87verma88 • Jan 23, 2009
Assuming that the bottle remains open the answer is yes. When the fly flies inside the bottle its wings will flap. The flapping wings will force the some air downwards. The air force in the downward direction will be equal to the fly's position in air(Newton's 3rd law).
The air pressure in the downward direction will be responsible for the increase in the scales reading. The change will be minute though.
If the bottle is closed then there will be no change as the force will be distributed along the side of the bottle.
Kaustubh Katdare • Jan 23, 2009
With that logic, we should also make sure that the measurements are taken at the time when no one in the world is sneezing. I bet it will affect the reading!
raj87verma88 • Jan 23, 2009
No, the farce will not be in the downward direction. If someone sneezes over the weighing machine then the reading may change. Again the change will be negligible unless you are measuring with an accuracy of 0.0000000001 Kg
shalini_goel14 • Jan 23, 2009
@SilverScorpion,