one of the key parts of the scientific method is the ability to make measurements. if i told you a...

One of the key parts of the scientific method is the ability to make measurements.

If I told you a measurement was 59.7. What would be your response?

The metric system is the one used in science. The units are called SI units-we will see that not all the units we will use are SI units.

SI base units are listed on p 34.

QuantityQuantity UnitUnit SymbolSymbol length meter m mass kilogram kg time second s current ampere A temperature Kelvin K amt. substance mole mol

3

NameName SymbolSymbol MultiplierMultiplier mega M 106

kilo k 103

deka da 10 deci d 10-1

centi c 10-2

4

NameName SymbolSymbol MultiplierMultiplier milli m 10-3

micro 10-6

nano n 10-9

pico p 10-12

femto f 10-15

5

You must know the following SI prefixes: Kilo-1000 Deci-0.1 Centi 0.01 Milli 0.001 Others will be provided.

Common Conversion Factors Length

◦ 1 m = 39.37 inches◦ 2.54 cm = 1 inch

Volume◦ 1 liter = 1.06 qt ◦ 1 qt = 0.946 liter

7

The SI base units are used to derive other units. Some are listed on page 36. One of the common derived units is volume. The SI unit for volume is the cubic meter (V=lxwxh) m3.

This is not a very practical unit to use in the lab.

The most commonly used metric units for volume are the liter (L) and the milliliter (mL).□A liter is a cube 1 dm

long on each side.□A milliliter is a cube 1

cm long on each side.

One important physical property of matter is density .

Density = mass/volume Every substance has its own unique density. See p 38 for a list.

There is some interesting info in the table. Notice the density of ice: 0.92g/cm3

and for water 0.998g/mL What do you think this means?

Since the density formula has 3 variables, 3 types of problems are possible.

D = m/V

1. given mass and volume-find density a substance has a mass of 23.2 grams and

a volume of 18.5 cm3. Find its density. 2. given density and volume, find mass (g) D = m/V so m=D x V The density of silver is 10.5 g/cm3. Find the

mass of a block of silver with a volume of 40.0cm3.

3. Given the density and mass, find the volume of a substance.

D= m/V so V= m/D Find the volume of a piece of iron that has a

mass of 147grams. ( density of iron = 7.86 g/cm3)

It is important to be able to convert one unit to another. We will make use of conversion factors (also known as unit factors). For example: how many grams are there in 25 kg?

What you need to know is how many grams there are in 1 kg. We know (or will know) that there are 1000g in one Kg (or 1 kg contains 1000 grams.

25 kg. X 1000 g = 25000 g. 1 kg

Some for you to try: a. 1.34 g to kg b. 15.2 cm to m c. 2580. mg to kg

Accuracy refers to the proximity of a measurement to the true value of a quantity.

Precision refers to the proximity of several measurements to each other.

If we happen to know the true or accepted value for a measurement then we can calculate the per cent error in our measurement. Percent error = (measured value-accepted value) X 100

accepted value

Every measurement has some uncertainty associated with it. See page 46. In every measurement there is a known or certain quantity and an estimated quantity.

In every measurement all the numbers are significant.

Many measuring instruments allow us to make an estimate of the last number in a measurement.

Piece of Black Paper – with rulers beside the edges1 2 3 4 5 6 7 8 9 10 11 12 13 14

12

34

56

78

9 22

Piece of Paper Side B – enlarged◦ How long is the paper to the best of your ability to measure it?

1 2 3 4 5 6 7 8 9 10 11 12 13 14

12

34

56

78

9

23

Piece of Paper Side A – enlarged◦ How wide is the paper to the best of your ability to

measure it?

1 2 3 4 5 6 7 8 9 10 11 12 13 14

12

34

56

78

9

24

Exact numbers◦ 1 dozen = 12 things for example

Accuracy ◦ how closely measured values agree with the

correct value Precision

◦ how closely individual measurements agree with each other

25

Significant figures◦ digits believed to be correct by the person

making the measurement

◦If you measured it-it’s significant Exact numbers have an infinite number

of significant figures12.000000000000000 = 1 dozenbecause it is an exact number

26

Significant Figures - Rules Leading zeroes are never significant

0.000357 has three significant figures Trailing zeroes may be significant

must specify significance by how the number is written

1300 nails - counted or weighed? Use scientific notation to remove doubt

2.40 x 103 has ? significant figures

27

Try these: How many significant figures are present in

each of the following measurements 236.5 g ______ 20.4 cm _____ 970 bricks _____ 92.00 kg ____ 946025.3709 miles ______

Multiplication & Division rule Easier of the two rulesProduct has the smallest number of significant

figures of multipliers

29

Multiplication & Division rule Easier of the two rulesProduct has the smallest number of significant

figures of multipliers

30

5.22 tooff round

21766.5

31.2x

224.4

Multiplication & Division rule Easier of the two rulesProduct has the smallest number of significant

figures of multipliers

31

5.22 tooff round

21766.5

31.2x

224.4

3.9 tooff round

89648.3

41.x

2783.2

Addition & Subtraction ruleMore subtle than the multiplication ruleAnswer contains smallest decimal place of the

addends.

32

Addition & Subtraction ruleMore subtle than the multiplication ruleAnswer contains smallest decimal place of the

addends.

33

6.95 tooff round

9463.6

20.2

423.1

3692.3

6.671 tooff round

6707.6

312.2

7793.8