why are these important?. si stands for systeme international d’unites internationally, this is...
Post on 22-Dec-2015
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MEASUREMENTS!Why are these important?
SI
SI stands for Systeme International d’Unites
Internationally, this is the system that we will use measure anything in science.
There are several things that get measured
Length, Mass, Volume/Area, Density, Time, Temperature
Length
Measured in Meters (m)
How long something is or the distance between two objects
Mass
Measured in grams (g)
The amount of matter in an object
Not the same as weight but similar
Area/Volume
Area is measured in m2
It is the amount of space on the surface something takes up.
Volume is measured in the liter (L) or m3
Amout of space something takes in 3D
Measuring a Liquid’s Volume
When measuring from a graduated cylinder or a beaker, measure at the bottom of the meniscus (natural curve that water makes in a container)
Density
Amount of matter that occupies a given space
Doesn’t have a special unit to itself.
Labeled g/mL or g/cm3
Aka mass/volume No tool to measure
Time
Internationally time is measured by seconds (s)
Usually is going to be measured by a watch or a timer
Temperature
In science we do no use the Fahrenheit scale. We use Celcius (C°)
We could also measure in Kelvin but that’s less important at the moment
Use a thermometer
Unit
Unit is whatever you are measuring in. It is described as any of the SI measurements that are used
Denoted with a u
Goes by 10’s
There are bigger and smaller units of each base units
Length-meter(m) Mass- gram (g) Volume- Liter (L) Time- second (s) Temperature-
Celcius (C°)
Prefixes will go in front of the base unit.
Prefixes are: kilo-, hecto-, deka-, deci-, centi-, milli-, micro-, nano-, pico-
King Henry Doesn’t [Usually] Drink Chocolate Milk
Goes by 10’s
Kilo(k)- kilogram (kg), kilometer (km), kiloliter (kL), kilosecond (ks), kilounit (ku)1ku= 1000 u (1000 of your base unit)
1u= .001 ku Hecto(h)- hectogram (hg), hectometer
(hm), hectoliter (hL), hectosecond (hs), hectounit (hu)1 hu= 100 u (100 of your base unit)
1 u= .01 hu
Goes by 10’s
Deka(D)- dekagram (Dg), dekameter (Dm), dekaliter (DL), dekasecond (Ds), dekaunit (Du)
1Du= 10 u (10 of your base unit) 1 u= .1 Du
Goes by 10’s
Deci(d)- decigram (dg), decimeter (dm), deciliter (dL), decisecond (ds), deciunit (du)
1 u= 10 du (10 du in your base unit) 1du = .1u Centi (c)- centigram (cg), centimeter
(cm), centiliter (cL), centisecond (cs), centiunit (cu)
1 u= 100 cu (100 cu in your base unit) 1cu= .01 u
Goes by 10’s
Milli (m)- milligram (mg), millimeter (mm), milliliter (mL), millisecond (ms), milliunit (mu)
1 u= 1000 mu (1000 mu in your base unit)
1 mu= .001 u
Quick Review….
Practice
1 m = ? mm
1ms= ? s
1 L = ? cL = ? mL
1 L = ? mm
HINT! If you are getting
bigger divide. If you are getting
smaller multiply
Measurement Uncertainty
Accuracy- is a measure of how close a measurement comes to the actual value of whatever is measured.
Ex. Darts land close to the bull’s-eye
Measurement Uncertainty
Precision- the measure of how close a series of measurements are to one another
Ex. The darts are all very closely grouped together. (Don’t have to be near bull’s-eye)
If something is precise it isn’t always accurate.
Questions
The density of a certain metal is 2.45 g/mL.
You measure densities of 2.01 g/mL, 1.99 g/mL and 2.03 g/mL. Accurate, precise, or both?
You measure densities of 2.45 g/mL, 2.50 g/mL, and 2.47 g/mL. Accurate, precise, or both?
You measure densities of 1.57 g/mL, 3.01 g/mL, and 2.45 g/mL
Finding Error
Accepted value- The correct value based on reliable references
Experimental value- The value measured in the lab
Finding Error
Error is the difference between the experimental value and the accepted value.
Error= experimental value- accepted value
The density of gold is 19.30 g/mL. You do a experiment and find a density for gold of 20.50 g/mL. What is the error in your experiment?
Finding Error
Error can be positive or negative depending on whether the experimental value is great than or less than the accepted value.
Percent error is the absolute value of the error divided by the accepted value, multiplied by 100%.
Percent error= error/(accepted value) x 100%
Gold PE = 1.20(g/mL)/19.30(g/mL)x 100% Gold PE = 6.21%
Scientific Notation
In many branches of science, some numbers are very small, while others are quite large. To convieniently express these numbers, scientists use a short hand called scientific notation.
Expresses a number as a multiplier and power of 10.
If the decimal point is shifted right the power of 10 is negative
If the decimal point is shifted to the left, the power of 10 is positive.
Significant Figures
I’m passing out a sheet. This is my reminder to myself… Don’t laugh at me