# Why can I put my hand through sand but not a table? [duplicate]

I've read in books that one can't put one's hand through a table because the table offers a "Normal Reaction" to the hand. And it is also stated that this force is electromagnetic in nature. But what is this force? Can it be explained using classical electromagnetism "in terms of something I'm more familiar with"?

Moreover, if it is this force that stops my hand from going through the table, why is it that certain other solid substances, like sand, don't produce the same result?

Also, is there any limit to this Normal reaction? I mean on pushing too hard my hand might go through the table. Is there any upper limit to this force?

• Well, to answer your last question, what happens when you push a hammer through the table as hard as you can? – Jerry Schirmer Jul 27 '15 at 17:05
• You can't really push your hand through sand - you can just push your hand between the grains. Each grain stays whole, the same as the table. – Harry Wilson Jul 27 '15 at 17:24
• Okay, but about the first part of my question? – Aritra Das Jul 27 '15 at 17:27
• possible duplicate of What does it mean for two objects to "touch"? – pentane Jul 27 '15 at 18:03
• Possible answer: here – john Jul 27 '15 at 18:18

You usually cannot push your hand through the table, because it's a single solid. The atoms are held together by covalent bonds, which are electromagnetic in nature. Sand on the other hand is grainy - the $SiO_2$ grains do not interact with each other and are only held "in place" because of gravity. You can run your hand through sand similar to driving a truck through a classroom full of tables, just by pushing them aside.