[ExI] scieceblind

[Adrian Tymes]

On Fri, Oct 13, 2017 at 10:20 AM, William Flynn Wallace
<foozler83 at gmail.com> wrote:
> No one of any age should be insulted when someone tries to cure their
> ignorance.  I don't mind being ignorant.  It's not shameful to me.  I just
> enjoy not being ignorant any more, so I am thankful to all who help me.

https://xkcd.com/1053/ puts my answer to this well enough.

> I still don't get some of it.  Say you take a less dense object and put it
> underwater.  Since it is less dense, does that mean that gravity pulls less
> on it?

Less *per unit volume*, yes.  In other words, gravity pulls less on it
than gravity pulls on an equal volume of water.

> And why should the water exert less of an upward force than on
> something more dense?  Or is it gravity?

Two things are being pulled by gravity into the same volume: the
object, and enough water to fill that same space.  Since the water is
being pulled on harder, the water gets in - and the object is forced
out.  The object has to go somewhere, and if you're out at sea (so "to
the sides" runs into "but the water over there is being pulled harder
too"), the only way to go is up - so, up the object goes.

(In theory, if you set up pipes and columns and stuff, an object could
be pushed to the side by this.  Something like that is exactly what
happens if the object is hit by a water cannon: although gravity is
not the source of the force, the water has enough force to try to push
the object aside.)

> If I were standing in a vacuum, would there be less holding me up since
> there is no air to exert an upward force on my body?  If this is correct, I
> am beginning to get it, eh?

Yes and no, though you are beginning to get it.  If you were in a
vacuum, yes there wouldn't be air trying to push you up - but there
also wouldn't be air above you trying to push you down.  Remember how
a table bears the weight of the book upon it?  You bear the weight of
the air above you.  Fortunately this is a very, very light weight, and
you're so used to it (having lived with it literally your entire life)
you don't notice.