Scientific MeasurementsScientific Measurements

The Scientific Method

A Way to Solve a Problem!

Key terms

• Hypothesis

• Law or principle

• Fact

• Theory

• Experiment

Hypothesis

• An educated guess; a reasonable explanation that is not fully accepted as factual until tested over and over again by experiment.

Law or principle

• A general hypothesis or statement about the relationship of a natural quantities that has been tested over and over again and has not been contradicted.

Fact

• A phenomenon about which competent observers can agree.

Theory

• Method and means of solving practical problems by applying the findings of science.

What is the Scientific Method?

• It is the steps someone takes to identify a question, develop a hypothesis, design and carry out steps or procedures to test the hypothesis, and document observations and findings to share with someone else.

• In other words, it’s a way to solve a problem.

Scientist have to take the time to think logically when they are investigating a question or problem.

• They break things down into many steps that make sense.

Scientists develop a question, gather information and form an hypothesis.

Scientific Investigations

• Science is the methodical exploration of nature followed by a logical explanation of the observations.

• Scientific investigation entails:– planning an investigation– carefully recording observations– gathering data– analyzing the results

The Scientific Method

• The scientific method is a systematic investigation of nature and requires proposing an explanation for the results of an experiment in the form of a general principle.

• The initial, tentative proposal of a scientific principle is called a hypothesis.

• After further investigation, the original hypothesis my rejected, revised, or elevated to the status of a scientific principle.

It is a series of steps (not always in this order)• Making observations => question• Formulating hypotheses => answering question

inferring, predicting. • Testing hypotheses. => experimenting,

communicating, collecting data, and measuring. • Formulating theories => Confirming hypotheses

that are supported by data. It includes constructing models, and predicting.

The Scientific Method

The Steps of the Scientific Method page 4 textbook

• 1- Recognize a question or problem.

• 2- Make an educated guess- hypothesis to the question.

• 3.- Make Prediction statements that explain hypothesis. (Research)

• 4. Perform test or Experiments

• 5- State Conclusion what did your experiment show? Did experiment confirm your hypothesis?

Application

How does the information you found relate to everyday life?

Uncertainty in Measurements• A measurement is a number with a unit attached.

• It is not possible to make exact measurements, and all measurements have uncertainty.

• We will generally use metric system units, these include.

– the meter, m, for length measurements

– the gram, g, for mass measurements

– the liter, L, for volume measurements

Length Measurements• Lets measure the length of a candy cane.

• Ruler A has 1 cm divisions, so we can estimate the length to ± 0.1 cm. The length is 4.2 ± 0.1 cm.

• Ruler B has 0.1 cm divisions, so we can estimate the length to ± 0.05 cm. The length is 4.25 ± 0.05 cm.

Uncertainty in Length

• Ruler A: 4.2 ± 0.1 cm; Ruler B: 4.25 ± 0.05 cm.

• Ruler A has more uncertainty than Ruler B.

• Ruler B gives a more precise measurement.

Mass Measurements

• The mass of an object is a measure of the amount of matter it posses.

• Mass is measured with a balance and is not affected by gravity.

• Mass and weight are not interchangeable.

Volume Measurements• Volume is the amount of space occupied by

a solid, liquid, or gas.

• There are several instruments for measuring volume, including:– graduated cylinder

– syringe

– buret

– pipet

– volumetric flask

Significant Digits

• Each number in a properly recorded measurement is a significant digit (or significant figure).

• The significant digits express the uncertainty in the measurement.

• When you count significant digits, start counting with the first non-zero number.

• Lets look at a reaction measured by three stopwatches.

Significant Digits Cont.• Stopwatch A is calibrated to seconds (±1 s),

Stopwatch B to tenths of a second (±0.1 s), and Stopwatch C to hundredths of a second (±0.01 s).

Significant Digits and Placeholders

• If a number is less than one, a placeholder zero is never significant.

• Therefore, 0.5 cm, 0.05 cm, and 0.005 cm all have one significant digit.

• If a number is greater than one, a placeholder zero is usually not significant.

• Therefore, 50 cm, 500 cm, and 5000 cm all have one significant digit.

Exact Numbers

• When we count something, it is an exact number.

• Significant digit rules do not apply to exact numbers.

• An example of an exact number: there are 3 coins on this slide.

Rounding Numbers

• All numbers from a measurement are significant. However, we often generate nonsignificant digits when performing calculations.

• We get rid of nonsignificant digits by rounding off numbers.

• There are four rules for rounding off numbers.

Rules for Rounding Numbers1. If the first nonsignificant digit is less than 5, drop all

nonsignificant digits.

Example:

A calculator displays 12.846239 and 3 significant digits are justified.

The first nonsignificant digit is a 4, so we drop all nonsignificant digits and get 12.8 as the answer.

2. If the first nonsignificant digit is greater than or equal to 5, increase the last significant digit by 1 and drop all nonsignificant digits.

A calculator display 12.856239 and 3 significant digits are justified.

The first nonsignificant digit is a 5, so the last significant digit is increased by one to 9, all the nonsignificant digits are dropped, and we get 12.9 as the answer.

Rules for Rounding Numbers

Rounding Numbers3. a) If the last digit is 5 and is preceded by an odd

number, then the last digit should be increased by . Example: 4.635 is rounded to 4.64

b) If the last digit is 5 but is preceded by an even number, then it stays the same or is rounded down by 1.

Example: 4.625 is rounded to 4.62.

4. If a calculation has two or more operations, retain all nonsignificant digits until the final operation and then round off the answer.

Adding & Subtracting Measurements

• When adding or subtracting measurements, the answer is limited by the value with the most uncertainty.

5 g

5.0 g

+ 5.00 g

15.00 g

• Lets add three mass measurements.

• The measurement 5 g has the greatest uncertainty (± 1 g).

• The correct answer is 15 g.

Multiplying & Dividing Measurements

• When multiplying or dividing measurements, the answer is limited by the value with the fewest significant figures.

• Lets multiply two length measurements.

5.15 cm × 2.3 cm = 11.845 cm2

• The measurement 2.3 cm has the fewest significant digits, two.

• The correct answer is 12 cm2.

Exponential Numbers

• Exponents are used to indicate that a number has been multiplied by itself.

• Exponents are written using a superscript; thus, 2×2×2×2 = 24.

• The number 4 is an exponent and indicates that the number 2 is multiplied by itself 4 times. It is read “2 to the fourth power”.

Powers of Ten• A power of 10 is a number that results when 10 is

raised to an exponential power.

• The power can be positive (number greater than 1) or negative (number less than 1).

Scientific Notation• Numbers in science are often very large or very

small. To avoid confusion, we use scientific notation.

• Scientific notation utilizes the significant digits in a measurement followed by a power of ten. The significant digits are expressed as a number between 1 and 10.

Applying Scientific Notation

• To use scientific notation, first place a decimal after the first nonzero digit in the number followed by the remaining significant digits.

• Indicate how many places the decimal is moved by the power of 10.

– A positive power of 10 indicates that the decimal moves to the left.

– A negative power of 10 indicates that the decimal moves to the right.

Scientific Notation Continued• There are 26,800,000,000,000,000,000,000

helium atoms in 1.00 L of helium gas. Express the number in scientific notation.

• Place the decimal after the 2, followed by the other significant digits.

• Count the number of places the decimal has moved to the left (22). Add the power of 10 to complete the scientific notation.

2.68 × 1022 atoms

Another Example• The typical length between two carbon atoms in a

molecule of benzene is 0.000000140 m. What is the length expressed in scientific notation?

• Place the decimal after the 1, followed by the other significant digits.

• Count the number of places the decimal has moved to the right (7). Add the power of 10 to complete the scientific notation.

1.40 × 10-7 m

• Accuracy = proximity of a measurement to the true value of a quantity.

• Precision = proximity of several measurements to each other.

Accuracy versus Precision

Summary

• A measurement is a number with an attached unit.

• All measurements have uncertainty.

• The uncertainty in a measurement is dictated by the calibration of the instrument used to make the measurement.

• Every number in a recorded measurement is a significant digit.

Summary Continued

• Place holding zeros are not significant digits.

• If a number does not have a decimal point, all nonzero numbers and all zeros between nonzero numbers are significant

• If a number has a decimal place, significant digits start with the first nonzero number and all digits to the right are also significant.

Summary Continued• When adding and subtracting numbers, the answer

is limited by the value with the most uncertainty.

• When multiplying and dividing numbers, the answer is limited by the number with the fewest significant figures.

• When rounding numbers, if the first nonsignificant digit is less than 5, drop the nonsignificant figures…If the number is 5 or more, raise the first significant number by one and drop all of the nonsignificant digits.

Summary Continued

• Exponents are used to indicate that a number is multiplied by itself n times.

• Scientific notation is used to express very large or very small numbers in a more convenient fashion.

• Scientific notation has the form D.DD × 10n, where D.DD are the significant figures (and is between 1 and 10) and n is the power of ten.

• 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.