# Physics 4A

```Physics 4A
Physics 4A
Chapter 1:
Measurement
Success in 4A
Units
General Schedule:
Tuesdays: PLC due by 4:00 pm
Wednesdays: 2 labs due every other Wed (1 formal)
Thursdays: HW due at 11:10 am; Quiz at 11:11 am
Recipe for Success in Physics 4A:
1) Read book and/or PowerPoint slides (HRW 9th edition)
before I lecture on the material.
2) After each lecture, review notes, work on cheat sheet, and
do the appropriate HW problems.
3) Finish HW by Tues. night so you can ask me, a PLC tutor,
or another student questions.
4) Review HW and notes on Wed. night for Thursday’s quiz.
Metric mishap caused loss of NASA orbiter
(CNN) -- NASA lost a \$125 million Mars
orbiter because a Lockheed Martin
engineering team used English units of
measurement while the agency's team
used the more conventional metric system
for a key spacecraft operation, according
to a review finding released Thursday.
Error points to nation's conversion lag
Lorelle Young, president of the U.S. Metric Association, said the loss of Climate
Orbiter brings up the &quot;untenable&quot; position of the United States in relation to most
other countries, which rely on the metric system for measurement. She was not
surprised at the error that arose.
&quot;Only the metric system should be used because that is the system science uses,&quot; she
said.
1
SI unit of length: meter (m)
⇒ In 1792, the meter was officially defined by
the French Academy of Sciences to be one tenmillionth of the distance from the north pole to
the equator.
A
Earth
C
Equator B
1m≡
SI unit of length: meter (m)
⇒ For practical reasons, in
1889, the meter was redefined
to be the distance between two
fine lines engraved near the
ends of a platinum-iridium bar.
AB
107
(The standard meter in 1889)
SI unit of length: meter (m)
⇒ In 1960, the meter was redefined as 1,650,763.73
wavelengths of a particular light emitted by an isotope
of krypton (krypton-86).
SI unit of mass: kilogram (kg)
⇒ The standard mass is a particular platinum-iridium
cylinder, kept at the International Bureau of Weights and
Measures near Paris, France, whose mass is defined to be
exactly 1 kg.
⇒ Finally, in 1983, the meter was redefined to the
definition that we use today.
Definition of the meter: “The meter is the length of
path traveled by light in a vacuum during a time
interval of 1/299,729,458 of a second.”
2
SI unit of mass: kilogram (kg)
⇒ When dealing with atoms and molecules, the
atomic mass unit (u) is usually used.
⇒ One atomic mass unit (u) is
defined to be 1/12 the mass of
the carbon-12 atom.
1 u = 1.66053886 &times; 10-27 kg
SI unit of time: second (s)
⇒ For many years, the
second was defined as
1/86,400 of a mean solar
day.
⇒ In 1967, the definition of the second was
defined to be the time for 9,192,631,770
oscillations of the light (of a specified
wavelength) emitted by a cesium-133 atom.
SI unit of time: second (s)
⇒ A cesium atomic clock
kept at the National Institute
of Standards and Technology
(NIST). This particular clock
keeps time with an accuracy of
~ 3 millionths of a second per
year.
⇒ The atomic clocks that are currently being developed will be
so accurate that they would have to run for more than 30 billion
years before they were off by 1.0 second.
3
```