Course Guide - USAID Teacher Education Project

sometimes straight, and sometimes obtuse. Think of a non-digital clock or watch.Note how the hands move around the center, and as they do the angle between thehands changes minute by minute.Take a look at this clock face, where the hours are not indicated in numerals, but inthe angles the hour hand will make when the minute hand reaches 12. Notice the lookof symmetry on the left- and right-hand sides of the clock face, and the gradualincrease in the angle from 12 to 6, and its angles from 6 to 12 as reflex angles that gobeyond the 6 o'clock straight angle.b) Angles are the space between two rays or line segments that meet at a vertex. Aclock face can help students understand that the size of the angle formed by two raysor line segments converging at (or emanating from) a vertex is NOT dependent on thelength of the line segments.Consider two clocks: Big Ben and a small bedside alarm clock. The pictures belowmight imply the two clocks are the same size, but Big Ben ("the largest four-facedchiming clock in the world") has a clock face of 7 metres (23 ft) in diameter. Comparethat to the little alarm clock that probably has a diameter of 6 cm.Yet both display the 30° angle indicating 1 o'clock. When considering angles, thesize of the clock face and the length of the hands are immaterial. The 30° angleremains constant.