Chapter 1 Physical Quantities and Units

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Chapter 1
In the quest to understand nature, scientists use
physical quantities to describe the world around
us.
Physical Quantities, Units, Measurements and
Estimation
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A real life story Gimli Glider
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Nasas Mars Climate Orbiter
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Two Teams, Two Measures Equaled One Lost
Spacecraft (New York Times, October 1,
1999) Simple confusion over whether measurements
were metric or not led to the loss of a 125
million spacecraft last week as it approached
Mars, the National Aeronautics and Space
Administration said on Thursday. An internal
review team at NASA's Jet Propulsion Laboratory
said in a preliminary conclusion that engineers
at Lockheed Martin Corporation, which had built
the spacecraft, specified certain measurements
about the spacecraft's thrust in pounds, an
English unit, but that NASA scientists thought
the information was in the metric measurement of
newtons. The resulting miscalculation,
undetected for months as the craft was designed,
built and launched, meant the craft, the Mars
Climate Orbiter, was off course by about 60 miles
as it approached Mars.
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Accuracy

• refers to the degree to which an experimental
  result agrees with the expected value.

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Precision

• different measuring instruments have different
  precisions.
• -Ruler 0.1 cm
• -Vernier calipers 0.01 cm
• -Micrometer screw gauge 0.001 cm

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Accuracy Precision

• Actual Height of Ms Tan 1.59 m
• Precise but not accurate answer 1.57 m
• Accurate and not precise answer 1.6 m

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Significant Figures
Example 1 7.12 ? 1.23 x 12 leave to
lowest sf Example 2 98.23 - 0.744
leave to lowest d.p Example 3 (5.65
0.0547) ? (0.11 x 5.4) finally to 2
sf
For multiplication and division
For additional and subtraction
Leave to 2 d.p
Leave to 2 sf
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Using prefixes
Speed of light 300 000 000 m/s Size
of atom 0.000000000010 m
Secret world.
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Prefixes
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Vernier caliper
http//www.members.shaw.ca/ron.blond/Vern.APPLET/i
ndex.html
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Micrometer Screw Gauge
http//www.members.shaw.ca/ron.blond/Micrometer.AP
PLET/index.html
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Zero Error
vernier calipers
When the two jaws of the vernier calipers touch
each other, both zero marks on the main scale and
on the vernier scale should coincide. If not,
there is a zero error in the vernier calipers.
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Zero Error
vernier calipers
If the two jaws touch each other, but the zero
marks of the main scale and vernier scale do not
coincide as shown below, the zero error is
positive.
0
1
main scale (fixed)
vernier scale (movable)
5
0
10
zero error 0.01 cm
supposing observed reading is 3.24 cm, then
corrected reading observed reading zero
error 3.24 (0.01)
3.23 cm
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Zero Error
vernier calipers
If the two jaws touch each other, but the zero
marks of the main scale and vernier scale do not
coincide as shown below, the zero error is
negative.
0
1
main scale (fixed)
vernier scale (movable)
5
0
10
zero error -0.02 cm
supposing observed reading is 4.03 cm, then
corrected reading observed reading zero
error 4.03 (-0.02)
4.05 cm
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Zero Error
micrometer screw gauge
Micrometers measure small diameters or
thicknesses.
anvil
spindle
sleeve
thimble
ratchet
frame
accuracy 0.01 mm / 0.001 cm
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Zero Error
micrometer screw gauge
sleeve
thimble
reading on sleeve 4.5 mm reading on thimble
0.12 mm actual reading of object 4.5
0.12 4.62 mm
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Zero Error
micrometer screw gauge
When the anvil and spindle of the micrometer
touch each other, the scales should read zero.
If not, there is a zero error in the micrometer.
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Zero Error
micrometer screw gauge
If the anvil and spindle touch each other, but
the scales do not read zero as shown below, the
zero error is positive.
supposing observed reading is 2.37 mm, then
corrected reading observed reading zero
error 2.37 (0.02)
2.35 mm
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Zero Error
micrometer screw gauge
If the anvil and spindle touch each other, but
the scales do not read zero as shown below, the
zero error is negative.
3 divisions
supposing observed reading is 2.87 mm, then
corrected reading observed reading zero
error 2.87 (-0.03)
2.90 mm