When the first ball is released, it hits the second ball and stops. For a split second, it appears that all the balls are motionless but what's actually happening is the energy the first ball had is transferred to the second ball. The energy, that the second ball now has, is transferred to the third ball and so on until the energy reaches the last ball. The last ball, not having anything to transfer the energy to, uses the energy to fly away from the other balls,
This transfer of energy, in one direction only, is a reasonable representation of what happens in direct current. Think of the first ball as an atom in a circuit's source, the three balls as atoms in the circuit's connection, the last ball as an atom in the circuit's load. (To complete the representation of a direct current circuit, we would need some way to transfer the energy the last ball receives back to the first ball, so the energy would continue to travel in one direction through a kind of loop.)
If we allow the Newton's cradle to continue, the last ball swings back into the fourth ball and the energy is passed back through the balls to the first ball, which flies away from the others just like the last ball did when it had the energy. This back and forth transfer of energy, in alternating directions, represents what occurs in a segment of an alternating current circuit. (As with the previous paragraph, we'd need some way to "connect" the first and last balls to represent a compete circuit rather than just a segment of a circuit.)
That's as far as we're going to go, at least for now, in mentioning alternating current. Instead, we're going back to focusing on the direct current (DC) circuits in a motorhome.
