Object of an Angle, Clip 2, 2:04

Notice he makes the move to ask about dropping a string down from the end of the cannon and using its length to compare the set up of each cannon. The students realize that the two strings will not have the same length. After a short discussion they realize that the distance of the string will not be the same. Thus they conclude that will not be sufficient for measuring an angle.

He does make a note of the arc drawn by a student and points out that it will be useful as they go on. Such a discussion may be necessary to ensure the students are focused on the issue of angle measure.