# Thread: gravity/weight of empty ball

1. question i've been haunted by: If i had a 1 pound worth of carbon fiber shaped into a ball(radius=6 inch) and extracted all the air, what would the ball weigh? and why. Does the negative space of a vacuum effect gravity field above or below ball? Any feedback is greatly appreciated.

2.

3. but if i filled it with helium it would be lighter?

4. Originally Posted by supanova
but if i filled it with helium it would be lighter?
It would weigh 1 kg plus the weight of the helium - ergo heavier (than one with vacuum inside).

5. Originally Posted by Dywyddyr
Originally Posted by supanova
but if i filled it with helium it would be lighter?
It would weigh 1 kg plus the weight of the helium - ergo heavier (than one with vacuum inside).

Bouyancy of helium at sea level would make it lighter, no?

6. Originally Posted by supanova
Originally Posted by Dywyddyr
Originally Posted by supanova
but if i filled it with helium it would be lighter?
It would weigh 1 kg plus the weight of the helium - ergo heavier (than one with vacuum inside).

Bouyancy of helium at sea level would make it lighter, no?
If you are accounting for the effects of buoyancy, then the vacuum filled sphere would be the lightest in terms of effective weight.

7. so say there is no carbon fiber and just say you have the vacuum...what would the buoyancy of the vacuum be? at sea level

8. Originally Posted by supanova
so say there is no carbon fiber and just say you have the vacuum...what would the buoyancy of the vacuum be? at sea level

9. so how did you come up with that number?

10. It's the weight of a 6 in radius sphere of air at sea level.

11. but this is not air. It's a vacuum that can magically hold a shape for arguments sake.

12. Originally Posted by supanova
question i've been haunted by: If i had a 1 pound worth of carbon fiber shaped into a ball(radius=6 inch) and extracted all the air, what would the ball weigh? and why. Does the negative space of a vacuum effect gravity field above or below ball? Any feedback is greatly appreciated.
Would you still be asking the same question if the air in the ball was replaced by molten lead?

13. Originally Posted by supanova
but this is not air. It's a vacuum that can magically hold a shape for arguments sake.
Which displaces that much air.

Look at it this way. Going back to your original idea. You take 1 lb of material and form it into a hollow sphere, enclosing air within. It still weighs 1 lb (enclosing the air does not change its effective weight.) Now remove the air, it now has an effective weight 1 lb minus the weight of the air you removed. That's the net buoyancy effect. (Another way to look at it is that the weight of the air in the sphere when you first enclosed it exactly cancels out the effect of buoyancy.)

Now magically remove the shell (1 lb) and you have a net weight of minus that of the air removed.

14. I've dropped the carbon ball part and now asking if a 6 inch raduis ball shaped vacuum has any buoyancy at sea level.

15. Originally Posted by Janus
Originally Posted by supanova
but this is not air. It's a vacuum that can magically hold a shape for arguments sake.
Which displaces that much air.

Look at it this way. Going back to your original idea. You take 1 lb of material and form it into a hollow sphere, enclosing air within. It still weighs 1 lb (enclosing the air does not change its effective weight.) Now remove the air, it now has an effective weight 1 lb minus the weight of the air you removed. That's the net buoyancy effect. (Another way to look at it is that the weight of the air in the sphere when you first enclosed it exactly cancels out the effect of buoyancy.)

Now magically remove the shell (1 lb) and you have a net weight of minus that of the air removed.

Thanks man. So a ball of helium would be buoyant and a ball of vacuum would be even more buoyant. But how much more buoyant?

16. Originally Posted by supanova
I've dropped the carbon ball part and now asking if a 6 inch raduis ball shaped vacuum has any buoyancy at sea level.

17. Originally Posted by Janus
Originally Posted by supanova
I've dropped the carbon ball part and now asking if a 6 inch raduis ball shaped vacuum has any buoyancy at sea level.
meant to quote rob before posting that.

18. Originally Posted by Dywyddyr
Originally Posted by supanova
but if i filled it with helium it would be lighter?
It would weigh 1 kg plus the weight of the helium - ergo heavier (than one with vacuum inside).
HTH would you weigh it though, given the buoyant effect of the helium? joc

19. Originally Posted by supanova
I've dropped the carbon ball part and now asking if a 6 inch raduis ball shaped vacuum has any buoyancy at sea level.
A ball of vacuum has NO buoyancy at any elevation, IMO. Practically, it cannot exist without confining media, and theoretically, in the absence of such media, it simply disappears as atmospheric air rushes in to fill the "void". Interesting idea, though! jocular

20. Just say i did have an ounce of magic material that could hold a vacuum the size of 6 inch radius ball. It would have no buoyancy? -or- would it still weigh 1 ounce? I'm no scientist but i think if i got 1 ounce of substance that usually takes up a certain amount of space and stretch it out to take more space it makes it lighter. Like a propane tank is lighter the less compressed it gets.

21. Originally Posted by supanova
Just say i did have an ounce of magic material that could hold a vacuum the size of 6 inch radius ball. It would have no buoyancy? -or- would it still weigh 1 ounce?
See post #8.

22. I think it would be lighter because it wouldn't have as much weight as the air sitting on top of it.

23. It's not hard. The buoyant force is equal to the weight of fluid displaced. Archimedes knew this before 200 BC.
Archimedes' principle - Wikipedia, the free encyclopedia

24. About 15 psi or so,at sea level.

25. nevermind i just don't understand. but does the empty space effect the magnetics from the earth on the molecules around the ball? above or below

26. Magnetic field? In carbon? Maybe if it were supercooled. Will it affect the gravitational attraction? Gravity is a mass mass relationship in curved space, inverse square, so it depends on the two masses. If they are unchanged, then there should be no changes in gravitational relationships.

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