Gauss-Codazzi equations are like a set of rules that help us understand how the shape of a surface changes as we move around on it. Imagine you're playing on a big bouncy castle. You can move around on it and it might even change shape a little bit as you move.
Now imagine you're a mathematician and you want to study the bouncy castle's shape in more detail. You could use Gauss-Codazzi equations to help you.
The first rule, called the Gauss equation, tells you how the bouncy castle is curved in different directions. It's a bit like looking at the surface of the bouncy castle from different angles - it might look very different depending on where you stand.
The second rule, called the Codazzi equation, is like a way of measuring the way the bouncy castle stretches and twists as you move around on it. Think of it like pulling on different parts of the bouncy castle - it will stretch and move in lots of different ways. By using the Codazzi equation, we can figure out exactly how it moves in different directions.
So basically, the Gauss-Codazzi equations are a set of rules that help us unlock the secrets of how surfaces like bouncy castles or even the Earth's crust change shape and move around.