Important Notes from AP Central: Beginning with the
2011 AP Exams, points will no longer be deducted for
wrong answers as they have been in the past. Studies
show that there is no difference in overall scoring
against norms when the point-deduction system is in
place versus when it is not. :-)
Why is this very good news for you?
Ch 1: Systems of Measurement Notes - Day 1
What is physics?
Evaluate the following scientists using the scale below:
0 = Never heard of this person
1 = Heard of them, but that’s about it
2 = Could accurately name / describe one theory / discovery made by them
3 = Could accurately name / describe morr than one theory / discovery made by them
1. Maxwell
3. Bernoulli
5. Einstein
7. Cavendish
9. Curie
11. Heisenberg
13. Aristotle
2. Joule
4. Becquerel
6. Galileo
8. Newton
10. Carnot
12. Bohr
14. Rontgen
What is meant by classical physics?
What is meant by modern physics?
Classwork: Classify the above scientists as either:
a classical physicist (C), a modern physicist (M), or both (B)
1-1 Units
What is meant by the abbreviation SI?
Why do we need it?
What are the SI units for:
a. length
b. mass
c. time
d. volume
e. force
f. energy
g. work
h. momentum
i. acceleration
j. density
What is a base unit? What is a derived unit?
Classwork: Classify letters a - j above as either B (base unit) or D (derived
unit).
Why is it important for you to be able to easily identify / derive the most
common units in physics?
See Table 1-1 on p 5 of your text. You need to know / memorize from tera, T,
down to pico, p.
1-2 Conversion of Units
What is a conversion factor?
See EX 1-1, p 7
Your employer sends you on a trip to a foreign country where the road signs
give distances in kilometers and automobile speedometers are calibrated in
kilometers / hour. If you drive 90 km/h, how fast are you going in:
a. m/s
b. miles/h
1-3 Dimensions of Physical Quantities
What is dimensional analysis? Why do we need to be able to use it?
See Table 1-2, p 7. Explain the meaning of each line. Translate them into SI.
Quantity
Symbol
Dimension
Area
A
L2
Volume
V
L3
Speed
v
L/T
Acceleration
a
L/T2
Force
F
ML/T2
Pressure (F/A)
p
M/LT2
Density (M/V)
d (book uses roe)
M/L3
Energy
E
ML2/T2
Power (E/T)
p
ML2/T3
SI equivalent
NOTE: As you go through the examples in the text, remember to look at the
Remarks section below each example.
They can really help add
understanding / perspective to each example, and to your overall knowledge of
the content! :-)
See EX 1-2, p 8
The pressure in a fluid in motion depends on its density, d, and its speed, v.
a. Find a simple combination of density and speed, in the M-L-T system that
gives the correct dimensions of pressure.
b. What are these units in SI?
1-4 Scientific Notation
What is the proper format for scientific notation? Why do we need to be able
to use it?
1-5 Sig Figs and Order of Magnitude
DEF: Sig Fig = a reliably known digit
What are the rules for determining whether or not a zero is significant?
What are the sig fig rules for multiplication / division?
What are the sig fig rules for addition / subtraction?
How does AP Central really feel about sig figs on the exam?
“Not everything that counts can be
counted, and not everything that can be
counted counts.”
Albert Einstein
How will the rest of your instructors / professors
feel about sig figs in coursework?
That is the rationale for the following statement: In this course, your
answers on all quizzes and tests MUST be expressed to the
correct number of sig figs.
REMEMBER: Parenthetically expressed numbers, conversion
factors, or any number you introduce into a problem do NOT
contribute to sig figs.
Only those numbers given in the
problem, and used to solve the problem, count!! The set-up
determines the sig fig rules for each problem.
DEF: Order of Magnitude = a number rounded off to its nearest power of 10
EX: size of chromosomes ~ 2 x 10 -6, thus, the order of magnitude is 10 -6
What is the order of magnitude for the height of a small insect if given by
8 x 10 -4 ?
See Table 1-3 on p 12. No need to commit to memory. Just some interesting
facts relating to order of magnitude.
See EX 1-3, p 8
In 12 g of carbon, there are 6.02 x 1023 atoms. (Recognize this number?) If
you could count 1 atom per second, how many years would it take you to count
the atoms in 1 g of carbon? Express your answer to 3 sig figs.
See EX 1-4, p 9
A liter (L) is the volume of a cube measuring 10 cm x 10 cm by 10 cm. If you
drink 1 liter of water, how much volume in cubic centimeters and in cubic
meters would it occupy in your stomach?
See EX 1-5, p 11
Find the sum of 1.040 and 0.21342.
DEF: Fermi question = a previously seemingly impossible question to answer,
unless one relies on estimated order of magnitude values. The following
example is one such question. You will note as we go through the problem, we
have to make an assumption about the thickness of the tread on an automobile
tire, or we won’t be able to do the problem at all!
The following definition is from WIKIPEDIA (and, it’s valid!!)
Fermi problem, Fermi question, or Fermi estimate is an
estimation problem designed to teach dimensional
analysis, approximation, and the importance of clearly
identifying one's assumptions. Named after physicist
Enrico Fermi, such problems typically involve making
justified guesses about quantities that seem impossible to
compute given limited available information.
See EX 1-6, p 12
What thickness of rubber tread is worn off the tire of an automobile as it
travels 1 km (0.6 miles)?
Assume tread thickness on a new tire is 1 cm.
Assume tires need to be replaced after about 60,000 km (37,000 miles)