# The Naked Scientists Forum

### Author Topic: When we fly do we gain or lose weight?  (Read 259 times)

#### vivian maxine

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##### When we fly do we gain or lose weight?
« on: 27/09/2016 12:35:55 »
I realize I can't (they say) compare apples and oranges; nor can I compare  the vacuum of space to the gravity of Earth with my question.  But I have to start somewhere to get this straight.

I keep reading that in space, if a "heavenly"  body (say an asteroid) picks up speed,  it will gain mass/weight.  This doesn't seem to make sense but perhaps it has to do with being in a vacuum.  I accept it as said.

That puzzle gets to my question back to Earth.  If a flying object (airplane) picks up more and more speed, is it also going to gain mass/weight?  It increases speed to overcome a certain amount of gravity.  Wouldn't it have less mass/weight as it went faster?  I thought the pull of gravity made us weigh more, not less.  So, if the plane overcomes a certain amount of gravity, wouldn't it weigh less?

#### alancalverd

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##### Re: When we fly do we gain or lose weight?
« Reply #1 on: 27/09/2016 16:53:10 »
You need to distinguish between mass (an inherent quantity of an object) and weight (the force of gravity on an object).

In the absence of gravity, or in any gravitational field, the mass of a stationary object or an object moving at constant speed is unchanged but its weight depends on the strength of the gravitational field.

In the case of a moving object, at very high speeds the effective mass increases according to the relativistic equation that you can find on the internet (I can't type equations in a legible form here!)

The relativistic mass gain by an airplane flying at any reasonable speed is negligible compared with the ablation of its surface by air friction.

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#### vivian maxine

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##### Re: When we fly do we gain or lose weight?
« Reply #2 on: 27/09/2016 20:37:45 »
Thank you.  So, they all gain mass whether in gravity or not.  I was stretching my imagination a bit in order to make my question fit airplanes.  I did realize they can't go so fast.  They'd become space ships. :-)  As for equations,  I not only can't type them; I can't read them.  Found out just recently that one I thought I learned in basic geometry is wrong.  Well, not wrong; just that we were taught wrong.  A friend says it's the same with her.  Not important.  I absorb without all the math.

I did read a very good article this morning distinguishing between mass and weight as well as talking about how it is used by the general public.  I must read that again.

Thanks again.  I think I understand and if i don't fully understand, I do know the answer. :-).  It still doesn't seem logical but a lot of science doesn't.  Yet it is proven.

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##### Re: When we fly do we gain or lose weight?
« Reply #2 on: 27/09/2016 20:37:45 »