We can easily move our hand in the air but to do the same through a solid block of wood we need a karate expert. Why?

We can easily move our hand in the air because the particles of air are loosely packed. The intermolecular spaces between the particles are large, and therefore the force of attraction is less. So, it is easy to break the force of attraction between the particles of air by moving the hand.

In case of a solid block of wood, the particles are closely packed. The intermolecular spaces are very less, and hence the force of attraction between the particles is very strong. So, it's not easy the break the strong force of attraction between the particles of a solid block of wood by moving the hand, and we need karate expert.