Physics

Equations: Momentum= mass x velocity,  Kinetic energy (KE)= 1/2 × mass × velocity2

Newton's cradle performs near elastic collisions. Although imperfect, the collision of any number of balls results in that same number being projected from the opposite end of the row. 

Conservation of momentum is clearly adhered to, and much of the kinetic energy is also conserved.As it does so, it's affected by the force of gravity, which works to slow the ball down. 

Coming back to Newton's Cradle, at rest, the balls have zero potential energy, as they can't move down any further (Potential Energy = mgh, at rest h = 0) and zero kinetic energy, since they aren't moving (Kinetic Energy = 1/2 mv2, at rest v = 0). 

The impact of one ball will move another ball of the same mass the same distance at the same speed

When one of the balls is lifted and released, it strikes the remaining stationary balls and sends force through all of them to push the ball on the other end away.

{Kinetic energy:Kinetic energy is the energy an object has because of its motion.| Potential energy: Stored energy that an object or system of objects may have based on their size, shape, position, or even material they are made from.| Momentum: product of the mass of a particle and its velocity}