Weight and temperature?

[Stargazer33]

Hi, I'm slightly confused/curious!

At work when I pick up my soldering iron I seem to be able to tell if it is turned on or not by how heavy it feels.  When it is turned off it seems to weigh less to me. Is there some sound physics going on here or have I just not taken enough medication today? 

I suppose I could just be subconsciously noticing a lack of heat and converting that in my brain as a lower weight but it really seems to weigh less to me.

[Alien 13]

I have to admit i have come across this with a soldering iron i am not sure if its the way its held (away from the tip with less pressure) when its thought it could be on.

Alan

[baggywrinkle]

It's all them little electical thingy bits burning off....the electrons, protons, neutrons and suppositrons..

Actually it should weigh the same.

[acey]

I suppose I could just be subconsciously noticing a lack of heat and converting that in my brain as a lower weight but it really seems to weigh less to me.

That sounds plausible - certainly the explanation for the effect (if it exists) must be psychological. But before seeking an explanation one should verify that there is something needing to be explained, by doing a blind test with many trials and finding out whether you really are able to make the judgment you claim at a rate better than chance. It is possible that "observer bias" is at play, and you notice the times when you get it "right" more often than when you get it "wrong".

In fact when a body is heated it does get heavier (thanks to relativity), but the effect is minute - way too small to measure in the case of something like a soldering iron. Instead you would need something like a star.

[Psychobilly]

Mine must get heavier ... I drop it far more often when it's hot....

Peter....

[bobmoss]

Mine must get heavier ... I drop it far more often when it's hot....

Peter....

I've done that a few times...

[Psychobilly]

I've done that a few times...

But do you still try and catch it....

Some days I do thousands of solder joints and tend yo put it back in the stand on auto-pilot... but occassionally There is an Instrumentation failure and the docking goes awry...

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[bobmoss]

But do you still try and catch it..

I've only done it once ;-)

[Psychobilly]

I think most off us have been there and done it - once that is ...

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[Earl]

Id say its a psycological thing, when its on you are far more aware of it in your hand than when its off, the increased awareness makes it feel heavier.

[davefrance]

Mine must get heavier ... I drop it far more often when it's hot....

Peter....

I find I drop mine less if I hold it by the handle. 

[Knight of Clear Skies]

Mine must get heavier ... I drop it far more often when it's hot....

Peter....

There is a similar phenomena concerning butter and toast. Clearly there is some new physics at work here, waiting to be unravelled.

[cgarry]

It's all them little electical thingy bits burning off....the electrons, protons, neutrons and suppositrons..

Actually it should weigh the same.

Actually it will be heavier (have more mass to be pedantic) when it is hot because of good old E = MC2. However, the mass increase will be tiny (because C squared is a big number) so I very much doubt you could sense it!

Cheers,

Chris

[ollypenrice]

I feel heavier when I get hotter. Take this afternoon, for instance. It was insanely hot and I was concreting, but when I sat in the shade and had a cold beer I felt a lot lighter (though I suppose my mass had gone up even more...) The experiment is flawed, though, because after the beer I decided not to try to stand up again and sat there having another one.

Olly

[Earl]

Actually it will be heavier (have more mass to be pedantic) when it is hot because of good old E = MC2. However, the mass increase will be tiny (because C squared is a big number) so I very much doubt you could sense it!

Cheers,

Chris

Would that energy been input not just be radiating off though?

[cgarry]

Would that energy been input not just be radiating off though?

indeed the energy will keep radiating off, which is why the soldering iron has to keep adding more energy to keep the iron at the same temperature.

However, the temperature difference between when the iron is off and when it is on represents the extra energy in the iron at the time.

Extra Energy = Temperature difference * Specific Heat Capacity * Mass of iron

No time to run through the maths now though!

[Tiki]

As the soldering iron heats up it of course expands, therefore it will weigh less on account of Archimedes Principle. The real question now I suppose are these effects enough to offset the relativistic mass increase?

[Paul M]

My late father knew all about this phenomena.

He had a habit of saying "that's hot!" if he picked up a heavy object and "that's heavy!" if he picked up a hot object.

Coincidentally, as a Radio Amateur he had an array of soldering irons.

Some were hotter, some were heavier, some were both and some were neither.

Weird...

[cgarry]

As the soldering iron heats up it of course expands, therefore it will weigh less on account of Archimedes Principle. The real question now I suppose are these effects enough to offset the relativistic mass increase?

Huh?  Are you saying there is mass loss due to thermal expansion?  That is news to me!

[jackruff]

After expansion it displaces more air and thus experiences slightly more buoyant force. But it's trivial. You will neither observe nor be able to measure any difference in the apparent weight of the soldering iron caused by temperature change.

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[Paul M]

After expansion it displaces more air and thus experiences slightly more buoyant force. But it's trivial. You will neither observe nor be able to measure any difference in the apparent weight of the soldering iron caused by temperature change.

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No you're wrong!

I've just tried an experiment.

I put my 25w Antex soldering iron on the kitchen scales cold. Then plugged it in. As it heated up the tip slowly pierced the plastic tray.

I was so amazed at how heavy it must have become to do that I forgot to look at the actual weight.

See, science in action!

[Tiki]

Are you saying there is mass loss due to thermal expansion?

No, only an apparent weight loss if we assume that the soldering iron is weighed in air (or some such fluid). A thermally expanded soldering iron 'floats better'.

[cgarry]

No, only an apparent weight loss if we assume that the soldering iron is weighed in air (or some such fluid). A thermally expanded soldering iron 'floats better'.

Ah yes, I am with you now.  The iron does not weigh less when hot, but does appear to weigh less due to the increased buoyant force from the air.

But as jackruff pointed out both the increased mass due to the increased energy and the increased buoyant force from the air are so tiny that they probably can't be measured let alone detected by a person.

[Stargazer33]

But do you still try and catch it....

Some days I do thousands of solder joints and tend yo put it back in the stand on auto-pilot... but occassionally There is an Instrumentation failure and the docking goes awry...

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We had a guy at work some years ago that managed to 'dock' his soldering iron in his cup of tea! It was only when the person sitting at the bench behind him asked what the hissing/sizzling sound was that he realised what he had done!

I would say that it is every time I pick the iron up and think that it is turned on when it isn't that I 'believe' it feels light. Obviously it is some strange coincidence/subconcious thing that is going on. however, I will continue to note my experiences for the greater scientific good!

[symesie04]

Could the cause of this be tension? I suspect that when you know thats its on (if even subconsoius) that there will be some aprehension when picking up a soldering iron which in turn cause some tension in the muscles of hand/arm. Tense muscles appear heavier than loose ones.