Ricky Goddard, The Beacon School, Surrey - Solids, Liquids and gases answer.
This is the superb answer to the question at the end of the solids, liquids and gases article:
I CAN WALK THROUGH AIR EASILY BECAUSE THE PARTICLES ARE VERY FAR APART AND EASY TO MOVE ROUND. MY BODY PUSHES THEM AWAY AS i WALK AND SO WALKING IS EASY WHEN I WALK THROUGH WATER THE WATER PARTICLES ARE MUCH CLOSER TOGETHER THAN THE AIR PARTICLES SO THERE IS NOT MUCH ROOM TO PUSH THEM AWAY. I MUST PUSH HARDER TO COMPRESS THE PARTICLES INTO SMALLER SPACES. THIS MEANS I MUST USE MORE FORCE. A WALL IS MADE OF PARTICLES THAT ARE HELD TOGETHER VERY TIGHTLY. THERE IS SO LITTLE SPACE BETWEEN THEM THAT THERE IS NO ROOM TO MOVE, ONLY VIBRATE. I MUST BREAK DOWN THE WALL TO SEPARATE ENOUGH PARTICLES FOR ME TO WALK THROUGH. SOME SOLIDS ARE WEAKER THAN OTHERS SO IF THE WALL WAS MADE OF JELLY I WOULD HAVE ENOUGH FORCE TO BREAK THE PARTICLES BUT IF IT WAS MADE OF BRICK I WOULD NOT HAVE ENOUGH FORCE (STRENGTH) TO DO THIS Super stuff - well done Ricky.