Why do middle balls in Newton's cradle move only after initial collision?

[jsmith613]

Homework Statement

http://www.lhup.edu/~dsimanek/scenario/Newton.htm

This is a good animation of how Newton's Cradle works

There was a question in an exam paper, Ed Jan 2011.

A student obsereved that when the raised ball collided weith the nearest stationary ball and stops. The ball furthest to the right moves away and the three middle balls remain stationairy. As time progressed the middle balls are also observed to be moving.

My question is: why initially don't the middle balls appear to move but eventually they do appear to move?

thanks

Homework Equations

The Attempt at a Solution

Ok so I understand that, in an ideal world, momentum and KE conservation dictate that however many balls are raised, that number of balls rise on collision.
However, this situation is not ideal and I cannot see how MOMENTUM conservation works
I know we are transferring energy to sound/internal energy of balls but how is momentum consereved (even when the balls stop) and why is the above situation fairly accurate?

 

[rcgldr]

That same website has a good explanation of what's involved:

http://www.lhup.edu/~dsimanek/scenario/cradle.htm