gravity

[excellent]

Is there gravity inside a vacuun?

[brachiopod]

Does a tree falling in a forest make a sound if there's no-one there to here it?

Gravity acts upon matter - simply put, an attractive force between masses.
A vacuum is an absence of matter.

If you put in a speck of matter to test if it is attracted by gravity, (which it will be), you no longer have a vacuum.

[Loosehead]

Gravity acts across a vacuum so the Moon is kept in orbit for example across the vacuum (ok pedants I know it's not a true vacuum, even in space there are add particles drifting about) in between. If you isolate an area of a vacuum then within that area there is no matter and hence as, Brachio points out, there would be no gravity.

[fo3nix]

I disagree. If there is gravity somewhere in space, then there is definitely gravity in a region of vacuum within that space.

So "excellent": if there is gravity somewhere in space, then there is also gravity in a region of vacuum within that space.

[Loosehead]

I meant no gravity source within the isolated area. Of course gravity traverses the vacuum.

[brachiopod]

Practical answer; Yes.

Philisophical answer; No.

[fo3nix]

ah ok, I misunderstood your answer in which case.

brachiopod: philosophical answer?

[brachiopod]

As per earlier answer;

You have a vacuum, into which you put something (a mass or particle of matter) in order to demonstrate the force of gravity acting within it, then it is no longer a vacuum. So it could be said that there is no gravity in a vacuum.

It's a bit of a Shroedinger's Cat or tree falling in forest making a sound type of argument.

The more practical answer is yes. As (say) a ball-bearing in a container that is otherwise a vacuum will be subject to the force of gravity.

I wasn't sure of the pitch of the question, and initially, I was going to say 'yes, of course there is'

[mimififi]

we did an experiment in school with a vacuum tube (big long glass thing with rubber tube coming out attached to some kind of noisy pump) and into it Mr Gulston (our science teacher) put a feather and a coin. When he turned the tube upside down and back again he was demonstrating something to do with the feather and the coin falling at the same rate as there being no uplift of air to slow the feather down. I assume that it was gravity pulling it down. But I don't really remember exactly all about that so....

That's all I have to say about that.

[mrbatfink]

Yes there can be gravity in a vacuum, it just has nothing to act upon. And yes a tree does make a noise when it falls even if no one is there to hear it.... The laws of physics don't change simply because man is not there to hear it, what a stupid sayiing

[fo3nix]

mrbatfink: it's not really that stupid at all. are you familiar with quantum mechancs? one of the weirdest things about it (lookup Schrodinger's cat experiment), is that if something is not observed, then it is not really there. As soon as it is observed, it is there (its wavefunction collapses).

[ShaghaiDoc]

It is not true that the laws of physics do not change because we are observing. e.g. an electron behaves differently when you observe it and when you do not observe it.