Sagnac effect

The Sagnac effect is a very interesting thing that happens when we move things around in circles. Imagine you're a kid playing with a toy car. If you put the car on a circular track and spin the track around, the car will move in a way that's different from when the track isn't moving.

This same thing happens when we send light around a circular path. When we send light in one direction, and then send it back in the opposite direction, the light behaves differently depending on if we're spinning the circle or not!

This is because light has a certain speed and distance it needs to cover. When we spin the circle, some parts of the light's path become shorter or longer than others, even though they're supposed to be the same length. This causes the light waves to get out of sync with each other, meaning they're not all at the same place at the same time anymore.

So, in short, the Sagnac effect is what happens when light waves get out of sync with each other because of a circular path that's moving. It's kind of like your toy car moving differently when it's on a spinning track!