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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 . A real life story… Gimli Glider. Nasa’s “Mars Climate Orbiter”.

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Chapter 1

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Chapter 1

Chapter 1

In the quest to understand nature, scientists use physical quantities to describe the world around us.

Physical Quantities, Units, Measurements and Estimation


Chapter 1

A real life story… Gimli Glider


Chapter 1

Nasa’s “Mars Climate Orbiter”


Chapter 1

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.


Chapter 1

Accuracy

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


Chapter 1

Precision

  • different measuring instruments have different precisions.

  • -Ruler = 0.1 cm

  • -Vernier calipers = 0.01 cm

  • -Micrometer screw gauge = 0.001 cm


Chapter 1

Actual Height of Ms Tan = 1.59 m

Precise but not accurate answer = 1.57 m

Accurate and not precise answer = 1.6 m

Accuracy & Precision


Chapter 1

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


Chapter 1

Using prefixes

Speed of light = 300 000 000 m/s

Size of atom = 0.000000000010 m

Secret world.


Prefixes

Prefixes


Chapter 1

Vernier caliper

http://www.members.shaw.ca/ron.blond/Vern.APPLET/index.html


Chapter 1

Micrometer Screw Gauge

http://www.members.shaw.ca/ron.blond/Micrometer.APPLET/index.html


Chapter 1

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.


Chapter 1

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


Chapter 1

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


Chapter 1

Zero Error

micrometer screw gauge

Micrometers measure small diameters or thicknesses.

anvil

spindle

sleeve

thimble

ratchet

frame

accuracy = 0.01 mm / 0.001 cm


Chapter 1

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


Chapter 1

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.


Chapter 1

} 2 divisions

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


Chapter 1

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


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