Con 1 units The Scientific Method 1. Observe the problem 2. collect data 3. search for laws that...

transcript

Con 1 units

The Scientific Method

• 1. Observe the problem

• 2. collect data

• 3. search for laws that describe the problem

• 4. form a hypothesis

• 5. form a theory

• 6. test or modify the theory.

Steps for the Scientific Method

Step # 1 – Observation

• Observation – the act of gathering information (data)– Qualitative data – information with NO

numbers • (hot, blue, rainy, cold)

– Quantitative data – information with numbers

• (98°F, 80% humidity, 0°C)

Step # 2 – Form a Hypothesis

• Hypothesis – tentative explanation for what has been observed

– There is no formal evidence at this point

– It is just a gut feeling

Steps for the Scientific MethodStep # 3 – Experimentation

Experimentation – a set of controlled observations that test the hypothesis

– Independent variable – the thing that you change in the experiment

– Dependant variable – the thing that changes because you changes the independent variable

– Constant – something that does not change during the experiment

– Control – the standard for comparison

For example…

• Let’s say we are going to do an experiment testing what happens when you heat and cool a balloon…

We will start with a balloon at room temperature

Now we will change something…

I will add heat to one balloon

What will happen to the balloon’s

It will expand

Now let’s cool things down

I will add cool down the balloon

What will happen to the balloon’s

It will get smaller

So what is what?• What variable did YOU change?

– Temperature

• What variable changes BECAUSE you changed the temperature?– Size of the balloon

• What is did not change in the experiment?– Amount of air in the balloon, what the balloon is

made of…

• What balloon did you use to compare the others to?– The room temperature balloon

(Independent Variable)

(Dependent Variable)

(Constant)

(Control)

Step # 4 – Conclusion

• Conclusion – judgment based on the information obtained

• There are seven base units in SI.

Base Units

• A base unit is a defined unit in a system of measurement that is based on an object or event in the physical world.

• A base unit is independent of other units.

• Some familiar quantities that are expressed in base units are time, length, mass, and temperature.

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Data Analysis: Basic ConceptsData Analysis: Basic ConceptsData Analysis: Basic ConceptsData Analysis: Basic Concepts

Base Units

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• Not all quantities can be measured with base units.

Derived Units

• For example, the SI unit for speed is meters per second (m/s).

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• Notice that meters per second includes two SI base units—the meter and the second. A unit that is defined by a combination of base units is called a derived unit.

Derived Units

• Two other quantities that are measured in derived units are volume and density.

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• Volume is the space occupied by an object.

Volume

• The derived unit for volume is the cubic meter, which is represented by a cube whose sides are all one meter in length.

• For measurements that you are likely to make, the more useful derived unit for volume is the cubic centimeter (cm3).

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• Scientists use two temperature scales.

Temperature Scales

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Temperature Scales

• THe defined the freezing point of water is 0 and the boiling point as 100.

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Temperature Scales• The Kelvin scale was devised

by a Scottish physicist and mathematician, William Thomson, who was known as Lord Kelvin.

• A kelvin (K) is the SI base unit of temperature.

• On the Kelvin scale, water freezes at about 273 K and boils at about 373 K.

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Significant Figures

• Scientist use significant figures to determine how precise a measurement is

• Significant digits in a measurement include all of the known digits plus one estimated digit

For example…• Look at the ruler below

• Each line is 0.1cm• You can read that the arrow is on 13.3 cm• However, using significant figures, you must

estimate the next digit• That would give you 13.30 cm

Let’s try this one

• Look at the ruler below

• What can you read before you estimate?

• 12.8 cm

• Now estimate the next digit…

• 12.85 cm

The same rules apply with all instruments

• The same rules apply

• Read to the last digit that you know

• Estimate the final digit

Let’s try graduated cylinders

• Look at the graduated cylinder below

• What can you read with confidence?• 56 ml• Now estimate the last digit• 56.0 ml

One more graduated cylinder

• Look at the cylinder below…

• What is the measurement?

• 53.5 ml

Rules for Significant figuresRule #1

• All non zero digits are ALWAYS significant

• How many significant digits are in the following numbers?

•274274

•25.63225.632

•8.9878.987

•3 Significant Figures3 Significant Figures

•5 Significant Digits5 Significant Digits

•4 Significant Figures4 Significant Figures

Rule #2

• All zeros between significant digits are ALWAYS significant

3 Significant Figures

5 Significant Digits

Rule #3

• All FINAL zeros to the right of the decimal ARE significant

19.000

105.0020

5 Significant Digits

Rule #4

• All zeros that act as place holders are NOT significant

• Another way to say this is: zeros are only significant if they are between significant digits OR are the very final thing at the end of a decimal

Rule #5

• All counting numbers and constants have an infinite number of significant digits

• For example:

1 hour = 60 minutes

12 inches = 1 foot

24 hours = 1 day

How many sig. Figs. Are in the following

numbers?

• 56784• 40002• 600• 34081000.00• 123.4005• 38726.000• 7162534• 100• 200.0004

Scientific Notation

• When numbers larger than 1 are expressed in scientific notation, the power of ten is positive.

• When numbers smaller than 1 are expressed in scientific notation, the power of ten is negative.

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• Remove the extra zeros at the end or beginning of the factor.

• Multiply the result by 10n where n equals the number of places moved.

Convert Data into Scientific Notation

• Remember to add units to the answers.

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Significant Digits in Calculations

• Now you know how to determine the number of significant digits in a number

• How do you decide what to do when adding, subtracting, multiplying, or dividing?

Rules for Addition and Subtraction

• When you add or subtract measurements, your answer must have the same number of decimal places as the one with the fewest

• For example:

20.4 + 1.322 + 83

= 104.722

Addition & Subtraction Continued

• Because you are adding, you need to look at the number of decimal places

20.4 + 1.322 + 83 = 104.722 (1) (3) (0)

• Since you are adding, your answer must have the same number of decimal places as the one with the fewest

• The fewest number of decimal places is 0• Therefore, you answer must be rounded to have 0

decimal places• Your answer becomes• 105

Rules for Multiplication & Division

• When you multiply and divide numbers you look at the TOTAL number of significant digits NOT just decimal places

• For example:

67.50 x 2.54

= 171.45

Multiplication & Division

• Because you are multiplying, you need to look at the total number of significant digits not just decimal places

67.50 x 2.54 = 171.45

(4) (3)

• Since you are multiplying, your answer must have the same number of significant digits as the one with the fewest

• The fewest number of significant digits is 3

• Therefore, you answer must be rounded to have 3 significant digits

• Your answer becomes

• 171

Accuracy vs. precision

• The quality of a measurement depends on the measuring instrument and the person making the measurement.

• Accuracy = how close the measurement is to the actual value.

• Precision = the agreement among the values for the measurement.

For Example…

• Let’s say we had the following dart board

Is the accuracy good or bad? Accuracy - GOOD

Is the precision good or bad? Precision - GOOD

Try this one

Is the accuracy good or bad? Accuracy - BAD

Is the precision good or bad? Precision - GOOD

Try this one

Is the accuracy good or bad? Accuracy - BAD

Is the precision good or bad? Precision - BAD

• Ways to determine density

• 1. regularly shaped objects – direct volume measurement.

• 2. Irregularly shaped objects- use water displacement method to fine volume.

• Density is a ratio that compares the mass of an object to its volume.

Density

• The units for density are often grams per cubic centimeter (g/cm3).

• You can calculate density using this equation:

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density

• D=m/v

• Density units always is g/cm3

• Mass is always in g

• Volume is always in cm3

• If it is not you must convert

• Note 1ml = 1cm3 ; 1 L = 1 dm3

Dimensional Analysis

• Dimensional analysis is just a big word for going from one unit to another.

• Have you ever converted inches into feet or years into days?

• If so, then you have done dimensional analysis

Dimensional Analysis

• Dimensional Analysis – method of problem-solving that focuses on changing units

• Conversion Factor – a ratio of equal values used to go from one unit to another– Example: 1 foot = 12 inches– Can be written as 1 foot

12 inches

Rules for Dimensional Analysis

1. ALWAYS start with the given!!!2. Draw a multiplication sign and a line3. Place the unit to be canceled on the bottom4. Place a conversion factor on the line you have

drawn5. Cross out units and see what you have left. 6. You must have one on top & one on the bottom

% error

• % error – the deviation from the accepted value during an experiment. Usually caused by human error.

• % error = your value - literature value x 100

• literature value

• It is always a positive number

• A graph is a visual display of data.

Graphing

• Using data to create a graph can help to reveal a pattern if one exists.

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Data Analysis: Additional ConceptsData Analysis: Additional Concepts Data Analysis: Additional ConceptsData Analysis: Additional Concepts

Circle graphs

• A circle graph is sometimes called a pie chart because it is divided into wedges like a pie or pizza.

• A circle graph is useful for showing parts of a fixed whole.

• The parts are usually labeled as percents with the circle as a whole representing 100%.

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Circle graphsTopic 3Topic 3

Bar graph• A bar graph often is used to show how a

quantity varies with factors such as time, location, or temperature.

• In those cases, the quantity being measured appears on the vertical axis (y-axis).

• The independent variable appears on the horizontal axis (x-axis).

• The relative heights of the bars show how the quantity varies.

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Bar graphTopic 3Topic 3

Line Graphs• In chemistry, most graphs that you create and

interpret will be line graphs.

• The points on a line graph represent the intersection of data for two variables.

• The dependent variable is plotted on the y-axis.

• Remember that the independent variable is the variable that a scientist deliberately changes during an experiment.

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Line GraphsTopic 3Topic 3

Line Graphs

• Sometimes points are scattered, the line cannot pass through all the data points.

• The line must be drawn so that about as many points fall above the line as fall below it.

• This line is called a best fit line.

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Line GraphsTopic 3Topic 3

Line Graphs

• If the best fit line is straight, there is a linear relationship between the variables and the variables are directly related.

• This relationship can be further described by the steepness, or slope, of the line.

• If the line rises to the right, the slope is positive.

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Line Graphs

• A positive slope indicates that the dependent variable increases as the independent variable increases.

• If the line sinks to the right, the slope is negative.

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Line Graphs

• A negative slope indicates that the dependent variable decreases as the independent variable increases.

• Either way, the slope of the graph is constant. You can use the data points to calculate the slope of the line.

• The slope is the change in y divided by the change in x.

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Interpreting Graphs• An organized approach can help you

understand the information on a graph.

• First, identify the independent and dependent variables.

• Look at the ranges of the data and consider what measurements were taken.

• Decide if the relationship between the variables is linear or nonlinear.

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Interpreting Graphs

• If the relationship is linear, is the slope positive or negative?

• If a graph has multiple lines or regions, study one area at a time.

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Interpreting Graphs

• When points on a line graph are connected, the data is considered continuous.

• You can read data from a graph that falls between measured points.

• This process is called interpolation.

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Interpreting Graphs

• You can extend the line beyond the plotted points and estimate values for the variables.

• This process is called extrapolation.

• Why might extrapolation be less reliable than interpolation?

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convert

• Convert the following• 8m to cm• 15 g to Kg• 85 Dm to mm• 6.7 cm to mm• 14.50 mm to m• 25 g to mg• 18 dg to mg• 200 Hm to cm• 52Km to dm

Con 1 units The Scientific Method 1. Observe the problem 2. collect data 3. search for laws that...

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