Review. Review Topics 1.Today: Review and Quiz 2.Test on Monday.

Review

Review Topics

1.Today: Review and Quiz

2.Test on Monday

Review Topics1. Quantity, Units, Prefix, symbol,

conversions

3. Rules of Significant numbers and calculations

5. Precision and Accuracy

7. Reading Scale

9. Uncertainty

How to Review

1. Experts stay in their station

2. Group members talk and expert collect info and write 10 points on the topic

3. Group members move to other groups after 5 minutes. Experts don’t leave their stations.

4. There will be four rounds of discussion, each of 5 minutes.

5. Experts come and present their points

1. Quantities, Units, Prefix

SI (International System) Base Units

Quantity Written Unit Unit Symbol

Length metre m

Mass gram g

Time second s

Amount of substance

mole mol

volume litre L

Magnitude

Prefix Unit

Exponent

Symbol Name Symbol name

2.5 10-2 C Centi M meter

2.5 cm

5. Convert 65 m2 to mm2

( )2 mm 2

1 m2

x 1 x 103

= 6.5 x 107 mm2

65 m2

Given that: 2.21 lb = 1.00 kg 4.54 L = 1.00 gal 1.00 atm = 101.3 kPa 1.61 km = 1.00 mile14 lb = 1 stone 2000 lb = 1 ton16 oz = 1 lb

4. 152 mL to gal

= 3.35 x 10-2 gal

4.54 L

x 1 gal

1000 mL

x 1 L152 mL

Round to 3 sig figs

Derived Quantities

3. Determine the mass of a 85.0 cm3 sample of lead.Do some research to find density of lead.Density = 11.34 g/cm3

85.0 cm3 x 11.34 g = 964 g 3 sig. figs.1 cm3

2. Significant Numbers

Significant figures

The number of meaningful digits in a measurement including the uncertain digit.

“sig figs”

2.5002 50.00650 35001 40.0200300 60.02010 4200 1200. 3 2.0 x 102 22. x 102 1

Types of Numbers

Measurements

2.5 cm long

Use sigfig rules

Defined Numbers

I min= 60 s

Do not use sigfig rules

Countable

25 students

Do not use sigfig rules

Multiplying and Dividing with Significant Figures

When multiplying or dividing numbers round the answer to the least number of significant figures found in any of the numbers used.

1.

V = distancetime

V = 25.3698 m = 13 m/min2.0 min

6 sig figs

2 sig figs

2 sig figs

Adding and Subtraction with Significant Figures

When adding or subtracting numbers round the answer to the largest decimal place found in the uncertain digits of any of the numbers used.

3.301.2256

- 0.36300.87 the largest decimal is the second

3. Precision and Accuracy

Types of Numbers

Inexact Numbers

Measurements

2.5 cm long

Use sigfig rules

Exact Numbers

Defined Numbers

I min= 60 s

Do not use sigfig rules

Countable

25 students

Do not use sigfig rules

Have uncertainty

Precision vs. Accuracy• Precision

– how closely individual measurements agree with each other

• Accuracy– how closely individual measurements agree with the

correct or true value

Good precision

Good accuracyand precision

Neither

Precision vs. Accuracy

4. Reading Scale

HOW TO READ A SCALE

How to Read Scale(Sigfig)

Certain Number

Numbered Divisions

Un-numbered Divisions

Uncertain Number

One uncertain number

HOW TO READ A SCALE

Reading of scale must include three kinds of numbers.

1.Numbered Divisions2.Unnumbered Divisions3.Guess (uncertain)

5.08 cm one uncertain

5. cm all certain

5.0 cm all certain

5. Uncertainty

HOW TO CALCULATE UNCERTAINTY

Only last digit is uncertain.

Never write like this 2.50 0.2cm

Decimal places of uncertainty MUST match the decimal places of the reading

Uncertainty Calculation

Measurements Range Scale

Average ± farthest Unit

Determine the average and uncertainty

5. 1.263 cm1.262 cm1.261 cm1.273 cm1.262 cm

1.262 0.001 cm

Uncertainty Calculation

Measurements Range Scale

Average ± farthest Unit

Exploring and Dealing with Uncertainty of Range

A measurement is in the range from 0.5128g to 0.5132g. what is uncertainty of the measurement?

Find mean: (0.5128 + 0.5132)/2 = 0.5130g

Find difference in the reading = 0.5132 - 0.5128 =0.0004 gDivide the difference by 2 = 0.0002

Now answer should be 0.5130 0.0002 g

Uncertainty Calculation

Measurements Range Scale

Average ± farthest Unit

Exploring and Dealing with Uncertainty of Scale

1.If a scale has 5 unnumbered divisions then uncertainty is 22.If a scale has 10 unnumbered divisions then uncertainty is 13.If a scale has 2 unnumbered divisions then uncertainty is 5

Now go to page 32 and find uncertainty of the scales given in question 48