Steve Saunders Goldwing Forums banner

1 - 20 of 82 Posts

·
Premium Member
Joined
·
1,650 Posts
Discussion Starter #1
I always wondered what the correct answer for these problems are:
Suppose you have this glass room entirely sealed from outside. It weighs 300 lb (just like my frigging doors) Inside we have a model helicopter on the floor. The air inside + the glass room + the helicopter weighs 320Lb.

Will the weight of this sealed room change once the helicopter hovers above the floor?
Id say no, but no scientific proof.

Second problem: we have the same room with something small combustibile inside . We remotely set this thing on fire and there is enough oxygen/air for it to burn completely.
Will the weight of the room change?
 

·
Registered
Joined
·
227 Posts
Here's my guess(es):

In the first instance, the mass of the combined objects does not change, but the measurable "weight" of the combined objects changes as the helicopter flies around and applies different amounts of downforce against the floor. At that point you're not measuring weight (alone) any more.

In the second instance the weight of the room will change, as all the mass that is converted into non-material forms of energy with mass escapes by radiation through the glass.
 

·
Premium Member
Joined
·
1,650 Posts
Discussion Starter #3
Hmm. I really like your avatar.I love animals.

Regarding the second answer I'm not sure energy has mass, though I heard someone say that a wound up spring it heavier that a relaxed one.

Is a charged battery heavier than a discharged one? Dont know
 

·
Premium Member
Joined
·
349 Posts
Scenario #1: While the helicopter is airborne, the room will be lighter by the same amount as the static weight of the helicopter. Once the helicopter lands, , , room weight will include the weight of the helicopter.


Scenario #2: The weight of the "small combustible mass" plus the weight of the detonator is included in the original "room weight". After the "burning" of the mass plus whatever amount of the detonator that burns will make the room lighter by however much the difference between original mass compared to burned mass plus the original weight of the detonator compared to the weight of the detonator AFTER detonation. Some mass will be lost, and so weight will be LOST.


**A 10 lb. log that is burned completely will NOT produce 10 lbs of ash
 

·
Administrator
Joined
·
24,390 Posts
I don't know but I think tamathumper is wrong on the first and right on the second.
Einstein said mass = energy or something like that & he seemed to be pretty smart. And a charged battery should weigh more than a discharged one, the electrolite's specific gravity is more when it's charged.
 

·
Registered
Joined
·
226 Posts
Here's my guess(es):

In the first instance, the mass of the combined objects does not change, but the measurable "weight" of the combined objects changes as the helicopter flies around and applies different amounts of downforce against the floor. At that point you're not measuring weight (alone) any more.

In the second instance the weight of the room will change, as all the mass that is converted into non-material forms of energy with mass escapes by radiation through the glass.
For the first instance, the original problem statement said the helicopter was hovering so the downforce applied by the helicopter will be equal to the static weight so the measured "weight" would be the same. The weight will fluctuate as the helicopter climbs (down force greater than static weight so "weight" will increase until the climb is stopped) or sinks (down force less than static weight so "weight" will decrease until the sink is stopped.

In the second instance the weight will not change. The energy that is released by combustion is stored in the chemical bonds of the material and/or the orbital energy of the electrons. When something burns the chemical bonds of the material and the oxidizer are changed (this includes the orbits of the electrons) but there is no mass converted into energy. (Mass into energy requires a nuclear reaction.) The radiation through the window allows the interior to cool but will not transfer any mass.
 

·
Registered
Joined
·
226 Posts
I don't know but I think tamathumper is wrong on the first and right on the second.
Einstein said mass = energy or something like that & he seemed to be pretty smart. And a charged battery should weigh more than a discharged one, the electrolite's specific gravity is more when it's charged.
A charged battery should weigh less than a discharged one since the charging process causes off gassing (some of the water in the acid is converted to hydrogen and oxygen). The specific gravity goes up because sulfate is being transferred from the plates in the battery back to the acid. So while the weight of the liquid goes up, the weight of the plates goes down. If you could charge a battery without creating any off gassing, the weight would remain the same.
 

·
Administrator
Joined
·
24,390 Posts
A charged battery should weigh less than a discharged one since the charging process causes off gassing (some of the water in the acid is converted to hydrogen and oxygen). The specific gravity goes up because sulfate is being transferred from the plates in the battery back to the acid. So while the weight of the liquid goes up, the weight of the plates goes down. If you could charge a battery without creating any off gassing, the weight would remain the same.
In a sealed battery?
 

·
Registered
Joined
·
552 Posts
In the combustion scenario some of the mass is converted to heat. Anybody figured out how to keep the heat inside, or weigh it?
 

·
Registered
Joined
·
226 Posts
In a sealed battery?

A sealed battery should weigh the same charged/discharged since the gases should stay inside the battery.

Off gassing can be minimized by regulating the voltage applied to the battery to just over the current battery output. There is a minimum voltage required to drive the conversion from water to hydrogen and oxygen. If you keep the charger voltage regulated to less than battery output plus conversion voltage the off gassing should be eliminated.

When I was growing up in the 70's we used to evaluate how well a car battery was charging by how many bubbles were coming out of the cell. More bubbles meant more current / better charging.
 

·
Registered
Joined
·
226 Posts
In the combustion scenario some of the mass is converted to heat. Anybody figured out how to keep the heat inside, or weigh it?
Combustion does not convert mass to heat

Graphite plus oxygen produces carbon dioxide

C + O2 -> CO2 with a heat of reaction of -395.3 kJ/mol

The weight of an atom does not change depending on the chemical compound it is in. The left side has one atom of carbon and two atoms of oxygen held in two compounds. The right side has one atom of carbon and two atoms of oxygen held in one compound.

The total weight of the system will not change when graphite is burned in oxygen when everything is inside a sealed container.
 

·
Premium Member
Joined
·
1,650 Posts
Discussion Starter #13
What a headache.
It is my opinion that in the first case the total weight will not change because of the enclosed system. It is the equivalent of a person jumping up and down in that room.
For a fraction of second when the person jumps the scale will measure higher then will be lower. However this does not change the weight.The average combined mass is always the same. Just because a person jumps up and down on a scale does not make him heavier or lighter.
Moreover, the helicopter could remain airborne only a limited amount of time.
The smaller the room the less time.
In conclusion the weight does not change in the first case.

Im still thinking about the second problem
 

·
Just one of the guys
Joined
·
4,774 Posts
The first one, i don't think it will change. I have no scientific reasoning, just my opinion. The helicopter goes from being supported by the floor to being supported by the air in the room. When the air is supporting the helicopter the total weight inside the room should stay the same.

In the second one the weight will be less. When something burns you get ashes, smoke and heat. The weight of the smoke and ashes will not be near the weight of the unburned material. Heat has no weight, in fact it will try to rise and, in sufficient amounts, could lift the room.
 

·
Administrator
Joined
·
24,390 Posts
A sealed battery should weigh the same charged/discharged since the gases should stay inside the battery.

Off gassing can be minimized by regulating the voltage applied to the battery to just over the current battery output. There is a minimum voltage required to drive the conversion from water to hydrogen and oxygen. If you keep the charger voltage regulated to less than battery output plus conversion voltage the off gassing should be eliminated.

When I was growing up in the 70's we used to evaluate how well a car battery was charging by how many bubbles were coming out of the cell. More bubbles meant more current / better charging.
It appears we have a scientist in our midst.
Do the electrons that leave the battery when being used have any weight?
Yes, I have used the bubbles method to check for charging, and way before the 70s.
 

·
Registered
Joined
·
226 Posts
It appears we have a scientist in our midst.
Do the electrons that leave the battery when being used have any weight?
Yes, I have used the bubbles method to check for charging, and way before the 70s.
The electrons have weight but for every one that leaves at the negative terminal, one enters at the positive terminal.
 

·
Registered
Joined
·
14 Posts
I don't know but I think tamathumper is wrong on the first and right on the second.
Einstein said mass = energy or something like that & he seemed to be pretty smart. And a charged battery should weigh more than a discharged one, the electrolite's specific gravity is more when it's charged.
True, the electrolyte gained weight, as evidenced by the specific gravity.

But that weight came from the plates. They are now lighter by an equivalent amount.

So, the result? You be the judge :)
 

·
Nobody You Know
Joined
·
272 Posts
I don't know the answer to either, but question 1 is a variation on the old "truckload of canaries" question. An enclosed truck is full of roosting canaries. The driver stops, gets out, and walks around the truck banging the sides, exciting the canaries, making them all go airborne. Does the weight of the truck change?
 

·
Administrator
Joined
·
24,390 Posts
I don't know the answer to either, but question 1 is a variation on the old "truckload of canaries" question. An enclosed truck is full of roosting canaries. The driver stops, gets out, and walks around the truck banging the sides, exciting the canaries, making them all go airborne. Does the weight of the truck change?
That would be the same thing as your question about the helicopter in a box.
 

·
Premium Member
Joined
·
1,650 Posts
Discussion Starter #20
Another problem:I saw this on "MYTHBUSTERS"
You drop a bullet from a certain height and measure the time it took to hit the ground then you shoot the bullet with a gun perfectly horizontal at the same height which one will take longer to hit the ground?
 
1 - 20 of 82 Posts
Top