Chapter 1

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					  Chapter 1

Doing Physics
                  Measurement

• We measure things (such as weight, time, length,
speed, etc.)

• We use tools (rulers, clocks, speedometers, etc.) to
measure things

• Measurement tools are calibrated

• Calibration is in units (inches, seconds, pounds,
mph’s, etc.)

• Units require standards (conventional, habitual,
customary)
               Modern standards

• Not all quantities in nature are independent (e.g.,
speed is distance per time)

• Standards are created for independent (base)
quantities: length, time, mass, + some other

• Modern day standards should be as invariable as
possible

• Should be uniformly defined

• Should be accessible
   SI (Systéme Internacional) – most
 accepted international system of units

• Adopted in 1971

• Is commonly known as metric system

• Standard units are (there are more):
1 m (meter) for length
1 s (second) for time
1 kg (kilogram) for mass

• All other SI units are defined as derivatives of the
base units (e.g., energy: 1 J (Joule) = 1 kg x 1 m2 / s2)
                        Length

• SI unit – m (meter)

• Initially adopted as one ten-millionth of a distance
between the North pole and the equator (standard –
platinum-iridium bar)

• Currently - a modern standard:

   1 m = the length of the path traveled by light in
 vacuum during a time interval of 1/299 792 458 of a
                        second
                         Time

• SI unit – s (second)

• Historically

1 s = 1 / 8640 day



• Currently - a modern standard:

  1 s = the duration of 9,192,631,770 periods of the
radiation corresponding to the transition between the
 two hyperfine levels of the ground state of the Cs133
                         atom
                         Time

• SI unit – s (second)

• Historically

1 s = 1 / 8640 day



• Currently - a modern standard:

  1 s = the duration of 9,192,631,770 periods of the
radiation corresponding to the transition between the
 two hyperfine levels of the ground state of the Cs133
                         atom
                           Mass

• SI unit – kg (kilogram)

• Historically 1 kg –
mass of 1 liter of water

• Initially adopted in prototype of the kilogram was
made of platinum-iridium and declared: “This
prototype shall henceforth be considered to be the
unit of mass”

• Currently - an alternative modern standard:

     1 kg = mass of C12 atom * 1026 / 1.99264824
(Don’t confuse mass and weight: 1 kg is the same on the Earth
                     and on the Moon)
Scientific notation


   237 000 000 s =
   = 2.37 x 108 s =
     = 2.37 E8 s

    0.0000664 m =
   = 6.64 x 10-5 m =
     = 6.64 E-5 m
          SI system prefixes

Factor   Name    Symbol   Factor   Name    Symbol
1024     yotta   Y        10-1     deci    d
1021     zetta   Z        10-2     centi   c
1018     exa     E        10-3     milli   m
1015     peta    P        10-6     micro   µ
1012     tera    T        10-9     nano    n
109      giga    G        10-12    pico    p
106      mega    M        10-15    femto   f
103      kilo    k        10-18    atto    a
102      hecto   h        10-21    zepto   z
101      deka    da       10-24    yocto   y


         Examples: 1.25E4 J = 12.5 kJ
           2.34 x 10-10 s = 0.234 ns
           Good SI web resource:



National Institute of Standards and Technology (NIST)

    http://physics.nist.gov/cuu/Units/
             Conversion of units

• Need to know a conversion factor
                1000 m
                       1
                 1 km
• Use chain-link conversion

            37 km  (37 km) (1)
            1000 m 
  (37 km)           37,000 m
            1 km 

(Check Appendix C for SI conversion factors)
Conversion of units
Conversion of units
                            Chapter 1
                           Problem 24
Highways in Canada have speed limits of 100 km/h. How does this compare
with the 65 mi/h speed limit common in the United States?
              Order of magnitude

• Order of magnitude is the power of 10 that applies

• Divide the number by the power of 10

• Compare the remaining value to 3.162 ( 10 )

• If the remainder is less than 3.162, the order of
magnitude is the power of 10 in the scientific notation

• If the remainder is greater than 3.162, the order of
magnitude is one more than the power of 10 in the
scientific notation
                              Chapter 1
                             Problem 39
The average American uses electrical energy at the rate of about 1.5 kilowatts
(kW). Solar energy reaches Earth’s surface at an average rate of about 300
watts on every square meter. What fraction of the United States’ land area
would have to be covered with 20% efficient solar cells to provide all of our
electrical energy?
Questions?
Answers to the even-numbered problems

Chapter 1

Problem 18:

(a) 15.6 m/s
(b) 51.3 ft/s
Answers to the even-numbered problems

Chapter 1

Problem 52:

42 km

				
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