So in newton's cradle when you drop the first ball why does only the last ball move and not the middle balls

Here is an example of Newton's Cradle:
http://www.school-for-champions.com/scie…

The force of the impact transfers through the balls very efficiently. When the first ball hits the second, that second ball wants to swing, but is already touching the third ball. So it pushes that third ball instead. The third ball does the same to the fourth, and the fourth does the same to the fifth. The fifth ball has no other ball to resist its movement, and so it swings.