Euler's rotation theorem

Euler's rotation theorem is like taking a toy figure and turning it around. Imagine you have a toy car and you want to play with it from different angles. If you move the toy car in any direction or rotate it, it will always be in the same position relative to a certain point.

Similarly, if you rotate a figure (or object) in three-dimensional space by a certain amount around an axis, you can always find a point that will stay fixed. This fixed point is called the "axis of rotation."

Euler's rotation theorem says that any rotation in three-dimensional space can be described by a single rotation around a fixed axis. This means that every rotation in three-dimensional space can be described by three numbers which represent the angle and direction of the axis of rotation.

So, essentially, Euler's rotation theorem is a way to describe any possible rotation of an object in three-dimensional space as a single rotation around a fixed axis.