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Scientific Method

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Scientific Method

- State Problem in question form
- Gather Information
- Hypothesis
- Experiment
- Data
- Conclusion- answer to the problem

Diet Coke and Mentos Guys

Diet coke and mentos guys I

- http://www.youtube.com/watch?v=hKoB0MHVBvM
- Diet coke and mentos guys II
- http://www.youtube.com/watch?v=I48hAOh3zJY&safe=active
- Myth busters
- http://www.youtube.com/watch?v=LjbJELjLgZg

Write up

- State the problem: What combination of soda and mints will produce the highest fountain?
- Gather info: What you already know or have looked up prior to this exp.
- Hypothesis: If I use ____ soda and ___ mints I will get the highest fountain.
- Experiment: Procedure step by step
- Data: organize and include in your write up = get from moodle
- Conclusion: 1) Restate your hypothesis as valid or not. 2) List sources of error. 3) Suggest ways to improve this experiment. 4) Suggest some other experiments with mints and soda.

Experiment

- Must have a control (what you compare to)
- Must test only one experimental variable
- Involves an independent variable (the one that is manipulated or changed by the experimenter)
- Involves a dependent variable (results of changing the independent variable)

Hypothesis VS. Theory

- An hypothesis is a prediction. Experiments are done to prove or disprove an hypothesis.
- A theory is a broad generalization. It is an explanation based on numerous repeated experiments.
- A model can be used as an explanation of data or phenomena observed over many experiments.

Observations

- Quantitative – involves numbers
- Qualitative – involves word descriptions

Measurement

- A comparison between an unknown quantity and a standard
- Standards kept at the Bureau of Weights and Measurement in Sevres, France and Gaithersburg, Maryland USA

SI UNITS

- SI = Systeme Internationale d’Unites
http://physics.nist.gov/cuu/Units/current.html

http://physics.nist.gov/cuu/Units/index.html

http://physics.nist.gov/cuu/Units/kilogram2.html

(kilogram)

- Fundamental or standard units (See pg. 34)
- Derived units - combo of standard units
- examples: density g/cm3, molar mass kg/mol
- SI prefixes: memorize table on pg 35
- http://www.i-am-bored.com/bored_link.cfm?link_id=47378

Bellwork podcast

http://www.youtube.com/watch?v=xbcn7FR3pdg&feature=player_embedded

Density= mass/volume

- A sample of metal has a mass of 8.4 g. The volume of the sample is 3.1 cm3. What is the density?
- Diamond has a density of 3.26 g/cm3. What is the mass of a diamond with a volume of 0.351 cm3?
- What is the volume of a sample of liquid mercury that has a mass of 76.2 g, given that the density of mercury is 13.6 g/cm3?
- The density of gold is 19.3 g/cm3. What is the volume of a sample of gold that has a mass of 0.715 kg?

Answers:

- 2.7 g/cm3
- 1.14 g
- 5.60ml
- 37.0 cm3

Percent error

- Percent error = Value exp – Value accept X 100%
value accept

- density of Al = 2.7 g/cm3
- You calculate Al = 1.7 g/cm3
- % error = 1.7 g/cm3 – 2.7 g/cm3 X 100%
2.7 g/cm3

- % error = 37%

Dimensional Analysis

- A technique that allows you to use units to solve a problem.
- quantity given X conversion factor = Quantity sought
- See pg 41.

- Precision-degree of exactness
- -depends on tool used
- -estimate last digit
-repeatable

- Accuracy-do results agree with a standard
- -calibrate with a known standard
- -is it the correct answer?

Significant figures

- Tell the precision of the instrument
- The last digit is the estimated digit (that is why the last zero is important!)
- See rules pg 47
- Can only express an answer as the least precise measurement

Determining the number of sig. figs. in a number.

- Picture a map of the U.S.
- If a decimal point is present, count from the Pacific side.
- Start counting with the first nonzero digit.
- All digits from here to the end, including zeros, are significant.

- If the decimal point is absent, start counting from the Atlantic side.
- Start with the first nonzero digit.
- All digits from here to the end, including zeros, are significant.

Rules for Addition and Subtraction

The number of sig. figs. is determined by the location of digits in the number with the largest uncertainty, not the number of significant figures in the number.

Examples:

The least precise number

is 2.02. It has sig. figs.

out to the hundredths

place. Therefore the

answer will have sig. figs.

out to the hundredths

place.

The least precise # (1.0236)

has decimals carried out 4

places. Therefore the

answer will have sig. figs.

carried out 4 decimal places.

Significant Figures in Calculations:

Rules for Multiplication and Division

The answer contains no more significant figures than the least precise number.

Examples:

The number with the

least # of sig. figs. has

2 sig. figs. Therefore, the

answer must have 2.

The number with the least

# of sig. figs. has 3 sig.

figs. Therefore, the

answer must have 3.

Powers of Ten

http://www.youtube.com/watch?v=0fKBhvDjuy0&feature=youtu.be

graphs

- k= y/x
- Directly proportional
- When y gets bigger so does x
- Create a straight line when graphed
- When rearranged: y=kx
- Which is the formula for a line: y=mx + b

graphs

- k= xy
- Inversely proportional
- When x gets bigger y gets smaller
- Graph is a hyperbola

Practice Test

- When converting mm to Hm what is the conversion factor?
- Answer 1Hm/100,000mm

Practice Test

- 0.046550 g rounded to two sig figs.
- 0.047 g
- 0.000406 How many sig figs?
- 3

Practice Test

- 0.0450 mm how many sig figs?
- 3
- 3020 cm How many sig figs?
- 3

Practice Test

- When 66.4 is divided by 3.00 How many sig figs will be in the answer?
- 3
- When 1.15 g, 2.667 g and 5.0 g are combined how many decimal spaces will the answer show?
- one

Practice Test

- Find the product of 15 cm and 2.3 cm. Express in proper sig figs.
- 34 cm
- Round to four sig figs 2.3456789 X 105
- 2.346 X 105

Practice Test

- Write in scientific notation 0.00000032 g
- 3.2 X 10-7
- 1.85 X 10-6 divided by 7.8 x 103 expressed to two sig figs is
- 2.4 x 10-10

Practice Test

- Which equation represents a direct proportion?
- A. xy=k
- B. X=k/y
- C. y=k/x
- D. k=y/x
- Answer D

Test Review

Know the following:

- Steps of Scientific Method
- Qualitative vs. quantitative
- Theory and hypothesis
- SI base units and derived units
- Precision vs. accuracy
- Independent variable vs. dependent variable
- The order of the SI prefixes

Test Review

- Why are there significant figures?
- Why is density a physical characteristic?
- Calculate: Density and percent error
- Count significant figures, calculate and express answer in proper sig. figs.
- Rounding
- Using conversion factors
- graphs