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Posted: 10/8/2007 4:53:32 AM EST
[Last Edit: 10/8/2007 7:16:45 AM EST by DangerousNinja]
There is a sealed jar sitting on a very sensitive scale with a fly in it.

Does the fly flying (compared to sitting still on the bottom) make a difference in the weight being shown on the scale?

The answer I have so far is that the scale will show a temporary increase in weight when the fly is starting to fly but when it is hovering it will read the same weight as when the fly is sittting still.

The question in a nut shell is this: Does a jar with a fly flying in it weigh more than if the fly was sitting still?

D_N
Link Posted: 10/8/2007 4:54:50 AM EST
This needs a poll.

But my guess is that the weight would remain constant.
Link Posted: 10/8/2007 4:59:27 AM EST
I don't know the answer but am signing on to this topic to view the responses.
Link Posted: 10/8/2007 4:59:45 AM EST
It'll read the same.
Link Posted: 10/8/2007 5:00:30 AM EST
The weight will be the same.

There may be a slight increase or decrease while the fly is landing, taking off, or while changing altitude...

But for constant hover flight, the weight of a jar with an airborne fly and a sitting fly will be the same.
Link Posted: 10/8/2007 5:01:01 AM EST
Depends if the jar is on a conveyor belt and if the fly has eaten any chili beans before being put in the jar.
Link Posted: 10/8/2007 5:01:28 AM EST
Why would it read the same?

The mass of the fly is no longer pressing against the bottom of the jar, and subsequently against the scale.

I say it will read lighter.
Link Posted: 10/8/2007 5:01:45 AM EST
[Last Edit: 10/8/2007 5:02:47 AM EST by Keith_J]
Covered in Mythbusters. Except birds in a trailer. No change.

They even tried it with an RC heliocopter.

Link Posted: 10/8/2007 5:02:07 AM EST
Since the jar is sealed I'm guessing the weight would remain constant.

Weight of the jar + weight of the air sealed in the in jar + weight of fly.

No matter where the fly is in the sealed system; I think the total weight would remain the same.

I think.

Link Posted: 10/8/2007 5:03:07 AM EST
It's like a buffer in an AR15. When the fly takes off the acceleration of the fly will show a momentary increase in weight. Conversely when the fly levels off the scale will show a momentary decrease in weight. These will average out to zero. There is no NET change in weight.
Link Posted: 10/8/2007 5:04:08 AM EST
i predict epic arguments in this thread.
Link Posted: 10/8/2007 5:04:11 AM EST
For the fly to fly in the jar its wings have to create a downward force equal to the weight of the fly. The force of the wings is against the air and the air in turn is against the jar. Because it is air, some may confuse the issue. It is no different than does a person weigh the same sitting or do they decrease in weight when they stand up. In the case of a person, the legs are creating a force equal to your weight. The only difference is that the air is fluid and your legs are solid.

So - the answer is, the weight is the same.

If you want to get technical the weight is slightly less because the force of gravity varies with the square of the distance between objects but thats a different subject.
Link Posted: 10/8/2007 5:04:23 AM EST
same weight.

Link Posted: 10/8/2007 5:04:25 AM EST
[Last Edit: 10/8/2007 5:04:49 AM EST by RSP]

Originally Posted By DangerousNinja:
The question in a nut shell is this: Does a jar with a fly flying in it weigh more than if the fly was sitting still?


No, this is the question in a nutshell, "Help! I'm in a nutshell!". Which raises another question, what happens if the fly is flying in a nutshell? And what happens if the question is in a nutshell, and raises another question? Does the newly raised question also raise the nutshell? What if the nutshell is raised into a flying fly? Is it harder or easier to raise?
Link Posted: 10/8/2007 5:05:38 AM EST
The weight remains the same because flying requires that you have a means to push air around your mass and offset the weight and consequently, generate some kind of lift. So the air pushing down on the weighing surface makes up for the weight being lifted.

Link Posted: 10/8/2007 5:06:10 AM EST
Same weight. They did this with a bunch of birds in a truck on Mythbusters.
Link Posted: 10/8/2007 5:06:55 AM EST

Originally Posted By RSP:

Originally Posted By DangerousNinja:
The question in a nut shell is this: Does a jar with a fly flying in it weigh more than if the fly was sitting still?


No, this is the question in a nutshell, "Help! I'm in a nutshell!". Which raises another question, what happens if the fly is flying in a nutshell? And what happens if the question is in a nutshell, and raises another question? Does the newly raised question also raise the nutshell? What if the nutshell is raised into a flying fly? Is it harder or easier to raise?


Or we could just throw the nuts back in the nut house. Off you go now.
Link Posted: 10/8/2007 5:07:34 AM EST
height=8
Originally Posted By Mister44:
Same weight. They did this with a bunch of birds in a truck on Mythbusters.


I believe they also illustrated this concept with their anti-gravity machine debunking episode.
Link Posted: 10/8/2007 5:08:52 AM EST
Closed system = same weight.
Link Posted: 10/8/2007 5:09:03 AM EST
Same weight. The fly at rest on the jar will be the same as the fly at a constant hover. The air pressure from the fly beating its wings will press against the bottom of the jar.

-Foxxz
Link Posted: 10/8/2007 5:12:20 AM EST
Wow, I didn't expect this many responses this quick! My friend who gave me my inital answer put it to me like this:

If you were on a scale and you weighed 200 pounds the scale would show 200 pounds. Now if you were to bend your knees and lower

your body it would show 200 pounds. If you were to stand up with alot of force the scale would show a temporary increase in weight.

Once you weren't moving it would show 200 pounds.
Link Posted: 10/8/2007 5:14:50 AM EST

Originally Posted By theblaze:
The weight will be the same.

There may be a slight increase or decrease while the fly is landing, taking off, or while changing altitude...

But for constant hover flight, the weight of a jar with an airborne fly and a sitting fly will be the same.


Roger. The scale will read the acceleration. It should read constant when the fly is not moving much either hovering or sitting on the bottom of the jar.
Link Posted: 10/8/2007 5:19:17 AM EST
I magine the fly was flying in water. The flies height in the water won't change anything. The air has mass so the example is a good one.
Link Posted: 10/8/2007 5:21:27 AM EST

Originally Posted By Mazeman:
same weight.


+1

unless the fly is on a conveyor belt.
Link Posted: 10/8/2007 5:22:09 AM EST
[Last Edit: 10/8/2007 5:23:27 AM EST by Melvinator2k0]
Weighs more\

Same
Link Posted: 10/8/2007 5:22:35 AM EST
[Last Edit: 10/8/2007 5:24:25 AM EST by mhoffman]

Originally Posted By Keith_J:
Covered in Mythbusters. Except birds in a trailer. No change.

They even tried it with an RC heliocopter.



+1

If the fly weighs 1 gram while resting, then there must be 1 gram worth of downward thrust exerted by its wings in order for it to fly. This thrust will be read by the scale just like the fly was when it was at rest.

_MaH

ETA: Quoted wrong post.
Link Posted: 10/8/2007 5:26:29 AM EST
I own all your fly page 2!

Weight is the same.
Link Posted: 10/8/2007 5:27:57 AM EST
[Last Edit: 10/8/2007 5:29:02 AM EST by Admiral_Crunch]
Don't try it outdoors!! The weight of all the air above the jar pressing down would destroy the jar and the scale.
Link Posted: 10/8/2007 5:32:29 AM EST
[Last Edit: 10/8/2007 10:08:00 PM EST by MEGR]
"Does a jar with a fly flying in it weigh more than if the fly was sitting still?"

The weight won't change (*edit meaning it won't increase when the fly is flying).

A digital scale uses load cells (strain gages) to measure weight. With no load acting upon the scale, the gages won't be strained and output a voltage (load is proportional to Vout/Vin). Think about it, say you're in a phone booth. Like this is a badass phone booth that's got thick doors and seals you in like a jar. You stand over a scale (not on it). There will be no change in weight, because you need a force to directly act upon it.

I've never seen the insides of a mechanical scale. I'd like to take it apart one day to see how it works.

Link Posted: 10/8/2007 5:37:25 AM EST
But the fly is burning calories while flying, turning mass into heat energy.

The fly will be losing weight, while it does not have any food or liquid to take in and replace its weight or fuel its caloric expenditure.

What does that do to the equation?
Link Posted: 10/8/2007 5:40:34 AM EST

Originally Posted By DangerousNinja:
Wow, I didn't expect this many responses this quick! My friend who gave me my inital answer put it to me like this:

If you were on a scale and you weighed 200 pounds the scale would show 200 pounds. Now if you were to bend your knees and lower

your body it would show 200 pounds. If you were to stand up with alot of force the scale would show a temporary increase in weight.

Once you weren't moving it would show 200 pounds.


Technically, yes, the acceleration of the fly could produce minute changes in the measured weight. But since flies don't weigh very much and can't accelerate very fast, you'd need a really sensitive scale to have a chance at seeing it, and it would probably be overpowered by other effects like air currents on the outside of the jar, vibration from people walking around on the ground, etc.

Link Posted: 10/8/2007 5:45:42 AM EST
It will weigh the same
Link Posted: 10/8/2007 5:45:56 AM EST

Originally Posted By chooper:
This needs a poll.

But my guess is that the weight would remain constant.


It will remain constant I think. The force required to lift the fly will just be applied on the jar. Didn't myth busters do this with pigens?
Link Posted: 10/8/2007 5:50:42 AM EST

Originally Posted By psyops4fun:
But the fly is burning calories while flying, turning mass into heat energy.

The fly will be losing weight, while it does not have any food or liquid to take in and replace its weight or fuel its caloric expenditure.

What does that do to the equation?


It isn't losing weight, because you can't turn mass into heat energy. Mass is conserved - it can't be created or destroyed, only moved around. The only time the fly's weight actually decreases is when it poos. What's being converted to heat is chemical energy, the way that the atoms are bound together. The atoms are rearranged when the fly converts its food into poo, and uses the energy to flap its wings, but the total number of atoms and the total weight of the system never changes.

(Well technically, nuclear reactions do change mass into heat energy. But that isn't really relevant unless you're in a nuclear reactor or a star or something.)

Link Posted: 10/8/2007 5:59:12 AM EST
What if there was a tiny hole poked into the top of the jar that let air in but did not let the fly out?
Link Posted: 10/8/2007 6:18:37 AM EST
does the scale measure mass?

IF you popped a human in a jar and put a strong spring under the jar and then the human jumped up, wouldn't the spring throw the jar up?

I don't get it.
Link Posted: 10/8/2007 6:23:39 AM EST
No difference at all. When the fly is in flight, the downdraft from its wings put as much pressure (on average over time) on the bottom of the jar as does the fly when it is just sitting.
Link Posted: 10/8/2007 6:24:04 AM EST
Conservation of mass.........


Stays the same.
Link Posted: 10/8/2007 6:24:33 AM EST

Originally Posted By mhoffman:

...If the fly weighs 1 gram while resting, that's one big damn fly.


FIFY
Link Posted: 10/8/2007 6:28:07 AM EST

Originally Posted By DangerousNinja:
There is a sealed jar sitting on a very sensitive scale with a fly in it.

Does the fly flying (compared to sitting still on the bottom) make a difference in the weight being shown on the scale?

The answer I have so far is that the scale will show a temporary increase in weight when the fly is starting to fly but when it is hovering it will read the same weight as when the fly is sittting still.

The question in a nut shell is this: Does a jar with a fly flying in it weigh more than if the fly was sitting still?

D_N


No, the mass (and in this case the weight) of the jar includes the jar, the air inside, and the fly....
Link Posted: 10/8/2007 7:15:55 AM EST
Lets increase the size of the question.

You have a gigantic sealed container that can hold a helicopter and has enough

room in it for the helicopter to fly around. The whole sealed container is on a scale.

Does the container weigh the same if the helicopter is hovering, taking off, or landed?
Link Posted: 10/8/2007 7:19:22 AM EST

Originally Posted By DangerousNinja:
Lets increase the size of the question.

You have a gigantic sealed container that can hold a helicopter and has enough

room in it for the helicopter to fly around. The whole sealed container is on a scale.

Does the container weigh the same if the helicopter is hovering, taking off, or landed?


Like I posted on page 1, the Mythbusters did it with birds and then an RC heli. NO CHANGE. END OF STORY.
Link Posted: 10/8/2007 7:19:28 AM EST
Does pushing down on a scale make it read a heavier weight? Yes. Does pushing down on a scale make your hand heavier? No. The weight would not change, regardless of the scale reading.
Link Posted: 10/8/2007 7:19:53 AM EST
There will be a difference. If the fly takes off he has to displace his weight using his wings, which in turn will push the scale down.
Link Posted: 10/8/2007 7:26:15 AM EST
[Last Edit: 10/8/2007 7:27:22 AM EST by Magurgle]

Originally Posted By Greenhorn:

Originally Posted By 1Andy2:
Why would it read the same?

The mass of the fly is no longer pressing against the bottom of the jar, and subsequently against the scale.

I say it will read lighter.


All the air above us is suspended in air - it's not touching the ground. Therefore there should be no air pressure.
Link Posted: 10/8/2007 7:28:57 AM EST

Originally Posted By DangerousNinja:
Lets increase the size of the question.

You have a gigantic sealed container that can hold a helicopter and has enough

room in it for the helicopter to fly around. The whole sealed container is on a scale.

Does the container weigh the same if the helicopter is hovering, taking off, or landed?




The concept remains the same, regardless of size. The weight remains the same.

Now if we incorporated a conveyor belt....

_MaH
Link Posted: 10/8/2007 7:34:15 AM EST
[Last Edit: 10/8/2007 7:34:46 AM EST by Dilbert_556]
What would happen if you replaced the glass jar with a container made of nylon mesh like a window screen, suspended by a string from the scale? Since there is a significant reduction in surface area for the air to push against, will the container be lighter while the fly flies?
Link Posted: 10/8/2007 7:34:45 AM EST

Originally Posted By BaxterStockman:
i predict epic arguments in this thread.


30 pages and a lock

My guess:

The down pressure of the flys wings would equal the weight of the fly and that would cause the weight to remain the same. Except when the fly is flying upside down, then all bets are off.

What if you had two flys and one was flying upside down and the other flying rightside up...?

IBTL
Link Posted: 10/8/2007 7:35:16 AM EST
Is there a vacuum in the jar?
Link Posted: 10/8/2007 7:36:16 AM EST

Originally Posted By Keith_J:

Originally Posted By DangerousNinja:
Lets increase the size of the question.

You have a gigantic sealed container that can hold a helicopter and has enough

room in it for the helicopter to fly around. The whole sealed container is on a scale.

Does the container weigh the same if the helicopter is hovering, taking off, or landed?


Like I posted on page 1, the Mythbusters did it with birds and then an RC heli. NO CHANGE. END OF STORY.


I question this because I don't know how the experiment was put together.

A bunch of birds in a semitrailer on a semi scale may not generate 20 pounds of downforce. Look at the weight of the trailer. It's got to be 10,000 pounds. What do the birds weigh? 100 pounds maximum?

I question the quickness of the scale and if it would register a quick 5 pounds of extra weight. If the trailer was at 10,001 pounds it may read 10,000 pounds. If it was 10,009 pounds it would read the same amount. Truck scales weigh to the 20s.
Link Posted: 10/8/2007 7:38:38 AM EST
[Last Edit: 10/8/2007 7:38:49 AM EST by RSP]
They used very sensitive touch sensors and a computer. I think they could tell even a couple ounces of difference.

Either way, if the heli is hovering it is supporting only its own weight on the bottom of the container - just as it would if it was sitting there normally.
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