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