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One Last Chapter 2 Thing
Mixture Pancake Batter, Orange Juice, Cement
SolutionSyrup, Apple Juice,
White Gold (mixture of Au and Pt atoms)
Solutions are mixtures, but not all mixtures are solutions.
Think of it this way: solutions (to anything!) are special.
The Basic UnitsPhysical Quantity Name of Unit Symbol
Length meter m
Mass kilogram kg
Time second s
Temperature kelvin K
Number of objects mole mol
Luminous intensity candela cd
Electric current ampere A
Those units are not the only rational choice.
Compound Units
•Velocity is a compound unit: distance over time: m/s or m-s-1
•Force is another: mass times acceleration: kg-m/s2 = 1 Newton
•Pressure is yet another: force over area = mass times acceleration over area
= (kg-m/s2)/m2 = Newton/m2 = Pascal
•There are many more (viscosity: g-cm-1s-1 = Poise)
Prefix Symbol Meaning
femto- F 10-15 = 1/1,000,000,000,000,000
pico- P 10-12 = 1/1,000,000,000,000nano- N 10-9 = 1/1,000,000,000
micro- 10-6 = 1/1,000,000
milli- m 10-3 = 1/1,000centi- c 10-2 = 1/100deci- c 10-1 = 1/10kilo- k 10+3 = 1000mega- M 10+6 = 1,000,000
giga- G 10+9 = 1,000,000,000tera- T 10+12 = 1,000,000,000,000
What is the gravitational acceleration in cgs units?
One
Unity = 1
2.54 cm = 1 inch
[2.54 cm/1 inch] = 1 = [1 inch/2.54 cm]
Compute the length of a football field in centimeters.
Compute the volume of rain, in gallons, that fell a football field (100 yards long x 50 yards wide) if the weather guy said we got
one inch of rain.
Break: Today’s AnnouncementsMonday, September 10 announcements
We are maybe one day behind—not bad, considering!
Ch 2 notes are essentially in final form.
New Appendix ABC notes are available.
Watch for a take-home exam to appear on website “soon”
You should have completed many of the assigned Ch. 2 problems.
Estimate the pressure on your feet when you stand up. Express the answer in pounds per square inch, and in nt/m2.
Estimate the pressure when you sit on your xxxx, in pounds per square inch, and in nt/m2.
oF = 32 + 1.8oC oC = (oF - 32)/1.8
K = oC + 273.15
Temperature: who the heck was Fahrenheit
Summer in Duluth
Body Temp. (Humans)
Winter in Duluth
Rectal temperature of the cow
Room Temperature
Liquid N2
16 oC = 61 oF
98.6 oF = 37 oC
-40 oF = -40 oC
100 oF
77 oC = 25 oC
77 K = -196.15 oC = -321oF
Convenient Temperature Conversions
Precision vs. Accuracy
Wrong Right Why
1.867 + 2 = 3.867
1.867 + 2 = 4
Addition/Subtraction: use least precise places1.867 +
2.000 = 4
1.867 + 2.000 = 3.867
"
1.867 x 2 = 3.734
1.867 x 2 = 4 Multiply/Divide: use smallest number of significant figures1.867 /
2.000 = 1
1.867/2.000 = 0.9355
"
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A Lost Art—Reading Gauges
What does it read? Don’t forget to guess! What if we had to put + and – on it?
23 3 For sure
23 1 Probably
Noise is Normal!
A balance that reads 1.00053 to 1.00055 is working!
A gauge that bounces around a bit is working!
(In fact, if it doesn't bounce, it might be stuck)
Exponential Notation
•Use it when it is EASIER. •Your calculator has an “E” button—learn how it works
To code in Avogadro’s number (we’ll see this later) push
6-.-0-2-3- E-2-3.
Remember the Rules!!!
(6 x 1023) x (3 x 1013) = 18 x 1036
Products: Add Exponents
(6 x 1023) / (3 x 1013) = 2 x 1010
Quotients: Subtract Exponents
Percent Errors
Suppose we measure a square tile, and find that each edge of the tile is L = 12.1 0.2 inches. What is % uncertainty?
Error Propagation
What is the uncertainty in the area of the square tile?