In this clip the teacher leads a discussion tying the period bar applet to the unit circle.
Sine Period Bar Applet , Clip 4, Recap, 1:48
This is an important discussion to have with the students.
In order to help the students verbalize how the outputs are related when the inputs are 2Pi apart, the teacher creates a table. When students have difficulty, he then draws a circle which will help make this connection.