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?