# Physics Question

My teacher was explaining why a rock sits on a table and doesn't move because of gravity. Apparently the surface area and thickness prevents the rock from going any further downward.

I asked my physics teacher if over time the rock would go through the table. He said probably not. I'm curious if an infinite time was used would the rock (theoritically(sp)) go through the table? Or would a table (in theory) eventually automatically collapse?

If not, I'm curious why.

If basic physics terms could be used it would be appreciated. I'm only on Newton's laws.

## Answers and Replies

BobG
Homework Helper
The reason has more to do with Chemistry than Physics (of course, the Chemistry involved has more to do with Physics than Chemistry, so...)

The force pulling the rock towards the center of the Earth isn't strong enough to break the bonds holding the molecules in the table together. The force definitely won't be strong enough to break the bonds in both the rock and the table (i.e. - you're not going to see the rock sink through the table). If it's a very heavy rock, you might 'snap' the bonds along an uneven line (i.e. break the table in half), but you'd almost certainly see some evidence right away (the table sagging, etc.).

Your gravitational force should stay pretty constant. An organic substance, such as wood, may undergo some chemical change that changes its strength, in which case the rock might eventually go through the table (the wood might rot, for example). Even a metal table could undergo some chemical change (rust, for example). The table's going to have to have some sort of chemical change occur that weakens the bonds among its molecules for the rock to eventually 'go through' the table.

I've got it. Thanks :)

Dear Dooga,

The Gravitational Force Keeps The Rock Down, But The Electrons Of The Rock And Of The Table Repel.
Therefore There Is A Balance Of Forces Involved, Which Causes The Rock To Stay Still.

Regards,

Roger