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