Question

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?

Answer 1

In air,

1. The intermolecular forces between the molecules of a gas are almost negligible.
2. The intermolecular spaces are very large.

Thus, we can easily move our hand in air, without any extra force.

In wood,

1. The intermolecular forces between the molecules of a solid are very large.
2. Intermolecular spaces are very small.

Thus, a lot of force is required to separate the molecules of wood. This is the reason we need a karate expert to break a block of wood.