Question

When we hands in the air we can easily move's but to do the same through a pack of wood? why?

Answer 1

Air, primarily made up of oxygen (for arguments sake) is a gas. The molecules in a gas are spread wide apart and so air is not very dense. 

A block of wood is a solid, meaning the molecules are packed tight together in a rigid formation. This means the object is very dense and so is much harder to penetrate.

Answer 2

Because Air being in gaseous state has got many inter molecular spaces in it but in wood particles are tightly packed so we can move our hands easily in air