01 phy quant 2 (length & time) (9jan8)
TRANSCRIPT
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Chapter1
Chapter1
Physical Quantities and UnitsPart 2 Length & Time
Physical Quantities and UnitsPart 2 Length & Time
In the quest to understand nature,scientists use physical quantities to
describe the world around us.
In the quest to understand nature,scientists use physical quantities to
describe the world around us.
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measurement of length and timemeasurement of length and time
accurate measurementaccurate measurement
There are two main types of errors:There are two main types of errors:
Random ErrorsRandom Errors Systematic ErrorsSystematic Errors
State random constant
Occurrence in all measurements observers estimate the
last figure of a readingon an instrument
observers consistentlyunderestimate oroverestimate a reading
Remedy reduced by averaginga large number ofreadings
minimised by methodof differences
No measurement is ever perfectly accurate. Even with highprecision instruments, some error is inevitable.
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One metre is the distance travelled by light in a
vacuum in 1/299792458 of a second.Q: What is the speed of light?
One metre is the distance travelled by light in a
vacuum in 1/299792458 of a second.Q: What is the speed of light?
measurement of lengthmeasurement of length
lengthlength
Length is the measurement of something fromone end to the other end.Length is the measurement of something fromone end to the other end.
has a SI unit of metre (m)
other units include centimetres (cm),millimetres (mm) and kilometres (km)
has a SI unit of metre (m)
other units include centimetres (cm),millimetres (mm) and kilometres (km)
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measurement of lengthmeasurement of length
lengthlength
measuring tape measuring tape
accuracy = 1 mm / 0.1 cm / 0.001 m
Lengths can be measured by using the following:Lengths can be measured by using the following:
accuracy = 1 mm / 0.1 cm / 0.001 m
metre/half-metre rule metre/half-metre rule
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measurement of lengthmeasurement of length
Parallax error is due to
incorrect positioning of the eye
the object is not at the same level as the markings of thescale
Parallax error is due to
incorrect positioning of the eye
the object is not at the same level as the markings of thescale
parallax errorparallax error
8.5 cmwrong
8.2 cmwrong
8.3 cmcorrect
The eye must be positioned perpendicularly at the mark onthe scale to avoid parallax error.The eye must be positioned perpendicularly at the mark onthe scale to avoid parallax error.
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measurement of lengthmeasurement of length
zero errorzero error
Many instruments do not read zero exactly whenthere is nothing being measured.
Reasons include:
Many instruments do not read zero exactly whenthere is nothing being measured.
Reasons include:
instruments are out of adjustment
some minor fault is present in the instrument
instruments are out of adjustment
some minor fault is present in the instrument
Instruments are usually still accurate as long as
the zero error is added or subtracted from thereading shown on the scale.
Instruments are usually still accurate as long as
the zero error is added or subtracted from thereading shown on the scale.
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engineers calipersengineers calipers
A pair of engineers calipers and ruler are used for measuringthe lengths of objects without any flat sides.A pair of engineers calipers and ruler are used for measuringthe lengths of objects without any flat sides.
measurement of lengthmeasurement of length
the jaws are closed untilthe points just touch theobject to be measured
remove the calipers andmeasure the distance between
the jaws with a ruler.
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Vernier calipers measure small lengths accurately up to0.01 cm.
Vernier calipers measure small lengths accurately up to0.01 cm.
vernier calipersvernier calipers
measurement of lengthmeasurement of length
accuracy = 0.1 mm / 0.01 cm
inside jaws
outside jaws
main scalevernier scale
tail
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reading on main scale (between A and B) = 2.4 cmreading on vernier scale (C) = 0.08 cmactual reading of object = 2.4 + 0.08
= 2.48 cm
vernier calipersvernier calipers
measurement of lengthmeasurement of length
main scale(fixed)
vernier scale(movable)
object being
measured
A B C
9 mm
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vernier calipersvernier calipers
measurement of lengthmeasurement of length
When the two jaws of the vernier calipers touch each other,both zero marks on the main scale and on the vernier scaleshould coincide.
If not, there is a zero error in the vernier calipers.
When the two jaws of the vernier calipers touch each other,both zero marks on the main scale and on the vernier scaleshould coincide.
If not, there is a zero error in the vernier calipers.
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supposing observed reading is 3.24 cm, thencorrected reading = observed reading zero error
= 3.24 (+0.01)
= 3.23 cm
measurement of lengthmeasurement of length
0 105
zero error = +0.01 cm
main scale
(fixed)
vernier scale(movable)
0 1
If the two jaws touch each other, but the zero marks of themain scale and vernier scale do not coincide as shownbelow, the zero error is positive.
If the two jaws touch each other, but the zero marks of themain scale and vernier scale do not coincide as shownbelow, the zero error is positive.
vernier calipersvernier calipers
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supposing observed reading is 4.03 cm, thencorrected reading = observed reading zero error
= 4.03 (-0.02)
= 4.05 cm
measurement of lengthmeasurement of length
0 10
zero error = -0.02 cm
main scale
(fixed)
vernier scale(movable)
0 1
If the two jaws touch each other, but the zero marks of themain scale and vernier scale do not coincide as shownbelow, the zero error is negative.
5
vernier calipersvernier calipers
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micrometer screw gaugemicrometer screw gauge
measurement of lengthmeasurement of length
accuracy = 0.01 mm / 0.001 cm
anvil spindle sleeve thimble ratchet
frame
Micrometers measure small diameters or thicknesses.Micrometers measure small diameters or thicknesses.
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micrometer screw gaugemicrometer screw gauge
measurement of lengthmeasurement of length
reading on sleeve = 4.5 mmreading on thimble = 0.12 mmactual reading of object = 4.5 + 0.12
= 4.62 mm
thimblesleeve
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measurement of lengthmeasurement of length
micrometer screw gaugemicrometer screw gauge
When the anvil and spindle of the micrometertouch each other, the scales should read zero.
If not, there is a zero error in the micrometer.
When the anvil and spindle of the micrometertouch each other, the scales should read zero.
If not, there is a zero error in the micrometer.
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measurement of lengthmeasurement of length
micrometer screw gaugemicrometer screw gauge
If the anvil and spindle touch each other, but the scales donot read zero as shown below, the zero error is positive.If the anvil and spindle touch each other, but the scales donot read zero as shown below, the zero error is positive.
supposing observed reading is 2.37 mm, thencorrected reading = observed reading zero error
= 2.37 (+0.02)
= 2.35 mm
supposing observed reading is 2.37 mm, thencorrected reading = observed reading zero error
= 2.37 (+0.02)
= 2.35 mm
} 2 divisions
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measurement of lengthmeasurement of length
micrometer screw gaugemicrometer screw gauge
If the anvil and spindle touch each other, but the scales donot read zero as shown below, the zero error is negative.If the anvil and spindle touch each other, but the scales donot read zero as shown below, the zero error is negative.
supposing observed reading is 2.87 mm, thencorrected reading = observed reading zero error
= 2.87 (-0.03)
= 2.90 mm
supposing observed reading is 2.87 mm, thencorrected reading = observed reading zero error
= 2.87 (-0.03)
= 2.90 mm
} 3 divisions
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measurement of timemeasurement of time
timetime
has a SI unit of second (s)
other units include years, months, days, hours,minutes and seconds
has a SI unit of second (s)
other units include years, months, days, hours,minutes and seconds
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measurement of timemeasurement of time
Time can be measured by using the following:Time can be measured by using the following:
analoguestopwatch
analoguestopwatch
digitalstopwatch
digitalstopwatch
clocks clocks
All timing devices make use of some regular process.All timing devices make use of some regular process.
timetime
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measurement of timemeasurement of time
Time can also bemeasured by using thefollowing simple pendulum.
Time can also bemeasured by using thefollowing simple pendulum.
oscillations are regularly
repeating motions the period is time in
which 1 oscillation occurs
oscillations are regularly
repeating motions the period is time inwhich 1 oscillation occurs
the period of a simple pendulumthe period of a simple pendulum
pendulum bobtied to one end
of a thread
BAO
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clocks make use of a processwhich is a regularly repeatingmotion (oscillations), such asthe swing of a pendulum
such oscillations are very
regular so period is regular
most modern clocks depend onthe vibration of quartz crystalsto keep time accurately
in clocks that are wound up,elastic potential energy is storedin coiled springs
clocks make use of a processwhich is a regularly repeatingmotion (oscillations), such asthe swing of a pendulum
such oscillations are very
regular so period is regular most modern clocks depend on
the vibration of quartz crystalsto keep time accurately
in clocks that are wound up,elastic potential energy is storedin coiled springs
measurement of timemeasurement of time
pendulum clock
(cuckoo clock)
pendulum clockpendulum clock
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used for measuring long intervalsof time
most modern watches depend onthe vibration of quartz crystals tokeep time accurately
the energy that keeps thesecrystals vibrating comes from asmall battery
many watches still make use of
coiled springs to supply the neededenergy
used for measuring long intervalsof time
most modern watches depend onthe vibration of quartz crystals tokeep time accurately
the energy that keeps thesecrystals vibrating comes from asmall battery
many watches still make use of
coiled springs to supply the neededenergy
watchwatch
measurement of timemeasurement of time
wrist watch
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A stopwatch is used to measure short intervals of time.A stopwatch is used to measure short intervals of time.
stopwatchstopwatch
accuracy = 0.1 s accuracy = 0.01 s
measurement of timemeasurement of time
stopwatches (analogue and digital) stopwatches (analogue and digital)
When using a digital stopwatch totime a race, the time to the nearest0.1 s should be given.
When using a digital stopwatch totime a race, the time to the nearest0.1 s should be given.
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ticker-tape timerticker-tape timer
measurement of timemeasurement of time
An electrical device that makes use of the oscillations of asteel strip to mark short intervals of time.An electrical device that makes use of the oscillations of asteel strip to mark short intervals of time.
steel strip
magnetcoil ticker-tape drawing pin
carbon paper disc6 ~ 12 V a.c.
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ticker-tape timerticker-tape timer
measurement of timemeasurement of time
10-dot tape10-dot tape
as there are 10 spaces on a piece of tape,
time taken for the tape to pass through the timer
= 10 x 0.02 s
= 0.20 s
between 2 consecutive dots, time interval = 1 s / 50 dots
= (1/50) s or 0.02 s
steel strip vibrates 50 times a second; therefore 50 dotsare made in a second on the paper tape
steel strip vibrates 50 times a second; therefore 50 dotsare made in a second on the paper tape
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e.g.
metre rulemetre rule
half-metre rulehalf-metre rule
measuring tapemeasuring tape
vernier calipersvernier calipers
micrometer screw gaugemicrometer screw gauge
pendulum clockpendulum clock
watchwatch
stopwatchstopwatch
ticker-tape timerticker-tape timer
length (m)length (m)
mass (kg)mass (kg)
time(s)time(s)electric current (A)electric current (A)
temperature (K)temperature (K)
amount of substance (mol)amount of substance (mol)
luminous intensity (cd)luminous intensity (cd)
PrefixesPrefixesMeasurementMeasurement
Physical quantitiesPhysical quantitiesare made upof
can bemeasured with
e.g. of
Numerical valuesNumerical valuesand suitable unitsand suitable units
VectorVector
ScalarScalarBase quantitiesBase quantitiesBase SI unitsBase SI units
TimeTimeLengthLength
micro (micro ()) 1010-6-6
milli (m)milli (m) 1010-3-3
centi (c)centi (c) 1010-2-2
deci (d)deci (d) 1010-1-1
kilo (k)kilo (k) 101033
mega (M)mega (M) 101066
maybe
include
usesuch as for
can bemeasured with