by meemoe_uk » Tue 01 Mar 2011, 13:13:22
$this->bbcode_second_pass_quote('meemoe_uk', 'B')ut in practice most if not all of the lifting energy comes from the Earth's gravity
>You have indicated that if someone dug a 10 km deep hole, and sat in it, then gravity would bring them back to the top of the earths crust.I'm sure that when POers read the sentance I wrote, they form crazy mental images similar to yours. I'm not responsible for the madness that goes on in POer heads. All I can say, assuming you've left nothing out, is that this is completely wrong, and my statement doesn't assert this at all.
Until you get a grip on gravitional energy only working in an up down direction, don't bother with trying to understand how gravity can lift stuff.
Although, if I'm having to tell you this, you probably are already doomed never to understand either situation.
You might want to see it with your own eyes though, even if you don't understand what you're seeing.
Here's how to see gravity lift something, step my step.
1. Stand up.
2. Walk away from computer.
3. Walk into kitchen
4. Get drink glass.
5. Fill drink glass with water.
6. Drop dense object into glass. e.g. metal spoon
7. Gravity will lift water in glass up, as object falls by gravity to bottom of glass. Without gravity, water would stay in the glass, until you pressed the spoon into the water, expending your own energy doing so.
Seeing this might make your brain spin. But it's a common aspect of reality. Kids are taught about it in there 1st few science lessons. It's exactly this mechanisn that brings oil deep in the ground, to the surface.
Finally, know this. Gravity isn't the only physics involved here, pressure is involved as well.