How does amplitude relate to the unit circle?
If you make the circle larger, then there is more difference beeen 'all the way up' and 'all the way down'
Say you are in a Ferris wheel, and we decide that the level of the axis of the wheel is called
Then your maximum height above the axis is one radius above
This height we call amplitude .
In other words: the amplitude is half the diameter (=the radius) of the circle.