In this clip the teacher leads a discussion tying the period bar applet to the unit circle.
Sine Period Bar Applet, Clip 2, 1:52
As the period bar is moved the students note that the bar is not changing in size and the teacher brings attention to this repsonse (which marks it as significant).
The students claim it is the period, but notice how the teacher continues to probe them until they justify their response. It is important to ensure that the students give meaningful responses in the terms used in the classroom.
The teacher makes the move to ask them whether it's a change in input or a change in output. This allows the discussion to turn to what happens when the input is increased by 2π. This discussion has the power to help students understand what period means.
