Unit 2 Measurements Flashcards
Measurement
A type of observation.
Qualitative Measurement
A measurement that uses descriptions.
Quantitative Measurements
Measurements made with a measuring instrument and includes a number and a unit.
Scientific Notation
A given number that is written as a product of numbers: a coefficient and 10 raised to a power.
Accuracy
How close a measurement comes to the actual or true value of whatever is measured.
Precision
How close a series of measurements are to one another.
% Error
The difference between an experimental value and the true value of a measurement. It tells you how close you were.
% Error Formula
% error = [(experimental - true) / true ] x 100
The goal for any percent error is?
0% - not realistic and a good %error is less than 5%
Uncertainty
Measurement is not definite or there is doubt in the measurement. All measurements have uncertainty, so the last digit is always a guess.
Significant Figures
All the digits that are known plus one last digit that is a guess.
The amount of sig figs depends on what?
The measuring instruement
Do exact numbers have uncertainty?
No, so they have an infinite number of sig figs.
Sig Fig Rule #1
all non-zeros are significant
Sig Fig Rule #2
all zeros in the middle of 2 non-zeros are significant
Sig Fig Rule #3
all zeros at the beginning before a non-zero are not significant
Sig Fig #4
zeros at the end of non-zeros are significant only if there is a decimal point written
Box & Dot Method of Sig Figs
Draw a box around all non-zeros beginning with the leftmost non-zero digit and ending with the rightmost non-zero in the number.
If a dot is present, draw a box around any zeros at the end.
Consider any and all boxed digits significant.
Rounding of Sig Figs
A rounded number has about the same value as the number you start with, but it has different precision.
Rounding Rule #1
If the number you are rounding is followed by 5, 6, 7, 8, or 9, round the number up; 5 and above, give it a shove.
Rounding Rule #2
If the number you are rounding is followed by 0, 1, 2, 3, 4, round the number down; 4 and below, let it go.
Multiplication/ Division of Sig Figs
The final answer is written so that it has the same number of sig figs as the number with the least number of sig figs.
Addition/ Subtraction of Sig Figs
The final answer is written so that it has the same number of decimals as the number with the least number of decimals.
International System of Units (SI)
The international standard for measurements is the metric system.
Any base until can be attached to a metric prefix (ex. centi, kilo, micro, milli, etc.
Mass
How much stuff an object contains.
Instrument = balance
SI Unit = kilogram (kg)
Base Unit = grams (g)
length
distance between two points
Instrument = ruler
SI Unit = meter (m)
Base Unit = grams (g)
Volume
how much space an object occupies
instrument = graduated cylinder
SI Unit = m cubed
Base Unit = liters (L)
Time
interval between 2 occurrances
instrument = clock
SI Unit = seconds (s)
Base unit = second(s) (sec)
temperature
how hot or cold something is
instrument = thermometer
SI Unit = Kelvin (K)
Base Unit = degrees Celsius (oC)
Dimensional Analysis
a method used to convert (or change) units
Equivalence Statements
are used to tell us how units relate to one another.
ex. 1L = 1000mL
Conversion Factors
Equivalence statements written as a fraction, which represents the relationship between the two different units.
Ex. 1ft = 12in can be written as 1/12 or 12/1
6 Steps for Dimensional Analysis
- read the entire question and find the equivalence statement you need.
- write your given number and unit over 1
- put a times sign (x) and a fraction bar
- put the units you have on the bottom of the fraction bar (so the units will cancel) and the units you want on the top of the fraction bar.
- fill in the number with the appropriate units. ALWAYS PUT THE 1 WITH THE BASE UNTIL AND THE OTHER NUMBER WITH THE PREFIX UNIT.
- calculate your answer. include proper units and sig figs. SIG FIGS ARE ALWAYS BASED ON THE NUMBER YOUR ARE GIVEN.
