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