Metallic roller bearing

Okay, so imagine you have a bunch of marbles in a jar. When you shake the jar, the marbles move around and bump into each other, right? That's kind of like what happens when machines move - the parts inside them bump into each other and create friction.

Now, imagine that instead of marbles, the jar was filled with smaller metal balls that were coated in a special substance that made them really smooth and slippery. When you shook the jar now, the metal balls would be able to move around even more easily - they would roll over each other instead of bumping into each other.

That's what a metallic roller bearing is - it's like those metal balls in the jar, but instead they are flattened slightly and put into a machine to help reduce friction. So when the machine moves, the roller bearings help the different parts of the machine move more smoothly and easily, which helps the machine work better and last longer.