Newton's Cradles vs Ball Bouncing off Wall
I was just reading about the working of Newton's Cradles and ended up having some confusion.
When a ball is taken to a certain height and dropped, it comes down and hits the next ball. Now the explanation as to why the first ball stops and doesn't bounce back is attributed to the law of conservation of momentum. Since momentum has direction, if the ball were to bounce back, the momentum would no longer be conserved as the direction would be reversed. Hence the momentum is transferred to the next ball.
Considering another situation, a ball bounces back when it hits a wall. The explanation given in this case is that the momentum of the ball changes from +mv to -mv and a momentum of 2mv is transferred to the wall, hence conserving momentum. Why can't this idea be applied to the case of Newton's Cradles as well?