2-1 A qualitative description is one with no measurements
A quantitative description provides numerical information
Scientific work requires a quantitative approach-certain
characteristics must be measured.
SI is the modern version of metric system and is based on
7 units of measurement:
Length= Meter (m)
Mass= Kilogram (Kg)
Time= Second (s)
Electric Current= Ampere (A)
Thermodynamic temperature= Kelvin (K)
Amount of Substance= Mole (mol)
Luminous Intensity= candela (cd)
The most commonly used measurements in science are
mass, length, time, and temperature.
SI prefixes-units are convenient because they are in multiples of 10.
Mega (M)= million (1X106)
* Kilo (k)= thousand (1X103)
Deci (d)= tenth (1X10-1)
*Centi (c)= hundredth (1X10-2)
*Milli (m)= thousandth (1X10-3)
Micro (u)= millionth (1X10-6)
Nano (n)= billionth (1X10-9)
Pico (p)= trillionth (1X10-12)
53 minutes= 1 microcentury
2-2 Mass and Weight
Weight is a measure of force gravity between two objects
Mass is a measure of the quantity of matter. Mass inertia of
is also a measure of the inertia of an object
*W= mg (comes from Newtons Law F=ma)
W M g
MKS N Kg 9.8 m/s 2
CGS dyne g 980 cm/s 2
FPS pound sl 32 ft/s 2
"Weigh" an object on a balance really means to get its mass!
Misnomer
2-3 Length- distance between 2 points
mks cgs fps
m cm ft.
2-4 Time- interval between 2 occurrences
seconds all measuring systems
2-5 Temperature
Thermometer normally measures temperature but thermocouple
optical pyrometer, and thermister are also used.
Average Kinetic energy of a group of particles is temperature.
Ek= 1/2mV2
Ep=mgh
Et=Ek +Ep
Absolute zero is the point where all molecular motion stops.
O degrees K
Metric- Celsius scale based on boiling (100 C)
and freezing (0 c) points of water
FPS- Fahrenheit scale based on boiling (212F) and freezing
(32F) points of water. Not used in text
K= C + 273
2-6 Accuracy and Precision
Accuracy refers to how close a measurement is to the true or
correct value for the quantity.
Precision refers to how close a set of measurements for quantity
are to one another (regardless if they are accurate).
2-7 Significant Digits
The last digit of a measurement is considered an estimate.
All digits that occupy places for which actual measurement was
made are called significant digits.
1- Digits other than zero are always significant
2-One or more final zeros after decimal point are always
significant
3-Zeros between 2 other significant digits are always
significant
4-Zeros used to place decimal are not significant
Significant really means measured- most of you probably think of
it as important. Nonsignificant digits are important as place
holders. 7000 g has 4 important digits but only 1 measured
or significant digit.
2-8 Numbers in Science
Scientific Notation- you can only be as accurate as your least
accurate number.
Multiply-add exponents
Divide - change exponent sign on bottom and add exponents.
Add or subtract exponents have to be the same.
proper scientific notation has one number to the left of the
decimal!
2-9 Derived Units
SI unit of volume is the cubic meter(m3)
1L = 1 cubic decimeter
1ml= 1 cubic centimeter(cc)
mks unit volume is liter(L) cgs unit is ml
speed is length per unit of time(ex. mph)
density is mass per unit of volume(ex. g/ml)
2-10 Problem Solving
1-write problem down
2-list known data (ex. mass=6g)
3-look for a known relationship or formula that has the data
that you are given(if you know everything given but 1
variable in a formula-you can work the problem). formulas
are really definitions or "laws"
4-circle your answer AND be SURE to include the unit!
2-11 Conversion Factors-are ratios with a value equivalent to one.
Ex. 1 inch = 2.54 cm or 1m=100cm
2-12 Factor Label Method is one way to solve problems. I will use
the Ratio and Proportion method because I find it easier to work with.
There is no right or wrong way-use the way you find the easiest to
understand!
Ex: 180 cm is how many meters?
100cm = cm known value 1m=100cm
X m m
therefore 180 cm = 100cm cross multiply
X cm 1m
100X= 180
X= 1.8 m (unit beside "X" is "m" so proper unit is "m")
2-13 Density
Density is mass per unit volume (definition)
D=m/v
Units- mks Kg/L
*cgs g/ml or g/cc