27 January 2011 Maths P04 Thu ● Text : Viola Ho Hours and minutes Have you noticed the angles between the hour and minute hands on a clock? These angles vary as the time changes 11 12 1 10 Consider a typical clock face. 2 The angle that each minute section makes = 360o/60 = 6o 3 9 The angle that each five-minute section makes = 6o x 5 = 30o 4 8 7 5 6 Movements of the hour hand Consider the hour between 12am to 1am. During the hour, the minute hand sweeps the clock face in one complete circle (360o). Question 30o Draw the hands on the clock faces as indicated. Have you noticed anything special about how the minute and hour hands move? 15o Note that the hour hand also moves, from 12 to 1, by one five-minute division (30o) at a time. 1 11 12 10 At 12.30am when half an hour has passed, the minute hand will have swept through 180o (360o/2). The hour hand will have swept through 15o (30o/2). The hour hand should be located at the mid-point between 12 and 1 on the clock face. 2 3 9 7 6 1 10 2 3 9 4 8 7 6 Vocabulary 11 12 5 1 10 2 3 9 4 8 7 6 Note that the angles between the hands at 12.30pm are different from the angles at 6pm. vary (v) 變更 typical (adj) 典型的 sweep (v) 擦過 division (n) 部份 2 3 9 4 8 7 5 2.15pm 6 5 9.45pm 2 11 12 1 10 2 3 9 4 8 7 6 5 10.05pm 5 1 10 4 8 11 12 11 12 11 12 1 1 10 2 3 9 4 8 7 6 5 8.25pm mid-point (n) 中央 indicate (v) 指示

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