Kirkendall effect

Okay kiddo, imagine you have a soccer ball and you're playing with your friends. You're kicking the ball back and forth, but one of your friends is a bit stronger than you and kicks the ball really hard.

Now, when the ball moves from you to your friend, it seems like it's moving really fast. However, when your friend kicks the ball back to you, it looks like it's moving slower.

This is kinda like the Kirkendall effect. It happens when two things (like two metal atoms) switch places. One of them moves faster than the other, which causes some weird stuff to happen to the atoms themselves.

Basically, the atoms on the slow-moving side end up moving a bit funny, which can make the metal really weak and brittle. So, it's like playing soccer where one person kicks the ball too hard and messes up the game.