# Possibly incredibly stupid question about gravity in an aeroplane

1. Apr 17, 2007

### jessb

I just want to make absolutely sure, but does anyone know if you actually do weigh less in a plane, and if you do, is it measurable?

Obviously a flying aeroplane, and not one on the ground ;)

Thanks! Jess

2. Apr 17, 2007

### ZapperZ

Staff Emeritus
You already weigh less when you are high up in the mountains. That's why places such as Denver, CO, and other cities up in the mountains have "thinner air".

Since an airplane travels higher than even these mountains, you can draw your own conclusion from there.

Zz.

3. Apr 17, 2007

### rewebster

except maybe on take off and in curves

4. Apr 17, 2007

### Hootenanny

Staff Emeritus
Your weight would still not change. Weight is a function of distance only, nothing else. Your apparent weight may change, i.e. the magnitude of the normal force from your seat.

5. Apr 17, 2007

### jessb

I guessed as much... but is it measurable? (on regular scales like you would have in your bathroom)

6. Apr 17, 2007

### rewebster

it seems to me, it would be when (a moment in time) and where (an exact location/circumstance in that moment of time) when you would weigh yourself (weigh less)---wouldn't you weigh less on the moon?

7. Apr 17, 2007

### jessb

I think what he was saying was that the pull of the earth on your body would still be the same in the plane if it was doing a parabolic flight and you appeared weightless, or if it was a regular flight and you didn't, so long as you were at the same distance from earth?

8. Apr 17, 2007

### lpfr

You weight less as you climb. But this is not the reason why the atmospheric pressure diminishes with height.
Atmospheric depends on the weight of the air column from de place you are until free space.
Although gravity diminishes with height, it does so far much slowly than atmospheric pressure.
As an example, in the summit of the Everest, gravity is only 0.25% lower than at sea level, but atmospheric pressure is just 35% of sea level pressure.

9. Apr 17, 2007

### AlephZero

Earth radius = 6400 Km (approx).
Typical cruise height of civil aircraft = 35,000 ft = 11 Km.

Change in gravitational attraction (a.k.a. weight) = (6400/6411)^2 = 0.996

A 0.4% change isn't hard to detect.

10. Apr 17, 2007

### ZapperZ

Staff Emeritus
It might, depending on how good your bathroom scale is (mine reads up to 1 decimal place).

The approximate difference in g between Denver, CO and sea level is about 0.06%. So for a 150 lb person, the change is weight between the two is about 0.1 lb. So yes, you can detect this with a bathroom scale.

Zz.

11. Apr 17, 2007

### rewebster

12. Apr 17, 2007

### jessb

Jess

13. Apr 17, 2007

### Hootenanny

Staff Emeritus
You would indeed weight less on the moon, but how many aeroplanes fly on the moon...

14. Apr 17, 2007

### rewebster

well since there's no aer on the moon---not many I would guess---

just nailing down the specific circumstance.

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If I'm not mistaken though, if you had the scale on the plane with you, and weighed yourself---I believe you'd weigh the same as if you weren't on the plane (on earth) and weighing yourself--I think it would depend on what type of scale you were using too.