Question

we can move our hand freely in air but why we have to broke ablock of wood with help of karate expert

Answer 1

THIS IS BECAUSE THE PARTICLES OF AIR MOVES FREELY AND LEAVES A LOTS OF SPACE BETWEEN THEM THUS WE ARE ABLE TO MOVE. BUT THE BLOCK OF WOOD IS SOLID AND IT'S PARTICLES ARE TIGHTLY PACKED AND IT RESIST THE MOVEMENT THROUGH IT AND THERE IS NO SPACE. THE KARATE EXPERT HAVE ENOUGH POWER TO BREAK IT.

Answer 2

Air is a gas, it has more space in between particles. But solid block of wood is rigid, hence it is difficult to move our hands through it.