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8/19/2019 C3 Time, Rate and Speed
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Time, Rate and
Speed
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3.1 Measuring Time
• Time is the duration of an event.
• Olden methods give inaccurate
measurements of time.• However, man has now developed more
accurate ways of measuring time.
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Units of time
• S.I. unit of time is the second, and
represented by the symbol s.
•Other units of time: minute min!, hour h!,millisecond ms!
• "ime can also be e#pressed in terms of
days, wee$s, months and years.
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Instruments to measure time
• "o measure a short period of time
accurately, we use a stopwatch.
•"here are two types: mechanical andelectronic.
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Instruments to measure time
• %echanical stopwatcho "he mechanical
stopwatch has a minute
scale and a second scale.o "he smallest division on
the mechanical stopwatchis &.' s.
o "hus, the mechanicalstopwatch is accurate to&.' s.
( mechanical stopwatch
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Instruments to measure time
• %echanical stopwatch1. )ress the
operating button to
start the stopwatch.
)ress the operating
button again to stop
the timing.
2. )ress this
button to reset
the stopwatch.
"he minute scale
"he second scale
"he second hand
indicates '*.+ s
"he minute hand falls
on the white area
between & and ' min
of the minute scale."his shows that the
second hand should
be read using the
second scale
between & and *& s.
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Instruments to measure time
• lectronic stopwatch
o "he electronic stopwatch is
more accurate than the
mechanical stopwatch.
o It can measure time intervals
accurate to &.&' s.
o It can also record the timeinterval in hours, unli$e the
mechanical stopwatch.
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Instruments to measure time
• lectronic stopwatch 1. )ress the -StartStop/button to start the stopwatch.
)ress the button again to
stop the timing.2. )ress this
button to reset
the stopwatch.
SecondsHours
%inutes
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3.2 What is Rate?
• ( rate is an e#pression of how one
0uantity changes with time.
• 1ates are useful for ma$ing fair
comparisons.
• )hone charges, internet access plans,
ban$ loan interest rates and inflation rate
are some e#amples of rates in real life.
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3.3 Speed
• Speed is the rate atwhich distance iscovered over time.
• Average speed isused to simplifycalculations since
speed may vary overthe duration of a 2ourney.
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3.3 Speed
• Average speed is the rate at
which total distance travelled
varies with the total time
ta$en.
• (verage speed 3 "otal distance"otal time
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3.3 Speed
• S.I. unit of speed is metre per second
(m/s.
• Other common units of speed: centimetre
per second cms! and $ilometre per hour
$mh!.
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Misce!!aneous
• http:en.wi$ipedia.orgwi$i"ime
• http:en.wi$ipedia.orgwi$i1ate
• http:en.wi$ipedia.orgwi$iSpeed• http:www.timeanddate.com
• http:www.nccc.gov.sgfueleconomyIntrod
uction.shtm• http:www.singstat.gov.sgstats$eyind.ht
ml