The bisector divides an angle into 2 equal parts. The movie shows, that if an angle bend is being produced in the way of matching angle's sides, the knuckle will be the bisector. A cross-point of all triangle bisectors is the center of an inscribed circle.
The altitude of a triangle drawn from its vertex is the perpendicular drawn from this vertex to the line containing the opposite side of the triangle. If a triangle stays on its side and a plummet is fixed at an opposite vertex than the plumb-line is the altitude of the triangle drawn from the vertex.
The median of a triangle drawn from its vertex is the segment joining this vertex to the midpoint of the opposite side of the triangle. In the movie a pasteboard triangle is putted down on an edge of a wedge. A triangle equilibrium may be obtained only if the edge is matched to the median. This happens because the median divides the triangle into the parts of equal areas.