The Scientific Method and International System of Units

The Scientific Method and International System of Units

What is "Science," how do we do it, and how is it communicated?

Science is a Process

Science is a method by which we determine what we can know about the world. "The Scientific Method" is a logical approach to solving problems by observing and collecting data, formulating hypotheses, testing hypotheses, and formulating theories that are support by data.

The Scientific Method in 7 Steps

• 1) Make an observation.

• 2) Ask a Question (or two or maybe even three).

• 3) Formulate a hypothesis that may explain the observation and the question that observation brought to mind.

• 4) Find a way to test ONLY that hypothesis, eliminating all confounding variables.

• 5) Perform the experiment.

• 6) Revisit your hypothesis, narrow its scope, expand its relevance, or reject it if it is disproven through experimentation. Then, repeat Step 4.

• 7) Once enough data is collected over many experiments in many different settings, a theory is developed.

Scientific experiments are conducted under controlled conditions in a specific portion of matter in a given region of space. This space is called a "system." The portion of the glass slide under the microscope would be the system being studied.

There are two types of data which can be observed

• "Qualitative Data" is descriptive. It tells us characteristics of the system we are working with.

• "Quantitative Data" is numerical. It tells us specific information about a system's mass, volume, or other numerically measurable qualities.

"Hypotheses" (plural of hypothesis) are testable statements which are developed via experimentation. They typically begin more generalized and become more narrow in scope as scientists collect more data through conducted experiments. They are most often written as if-then statements. The if part contains the conditions of the observed phenomena and the then part contains the prediction of the hypothesis.

In an experiment, there are controls and variables

• Controls - experimental conditions which remain constant throughout the experiment

• Variables - experimental conditions which change

Variables are the aspect of the phenomena which is being studied.

Controls are aspects of the phenomena which we either understand or are not currently interested in.

Theorizing

Over time, when enough data is collected to back up a hypothesis, the hypothesis becomes a theory. A theory is a broad generalization that explains a body of facts or phenomena. Many times, theories are communicated through a model which is an explanation of how phenomena occur and how data or events are related.

Essentially, theories explain why something happens while laws explain what happens

Multiple Choice

You have made an observation. Before moving on to experimentation, what must you do?

• Produce a rigorously tested theory

• Form a hypothesis

• Revisit your hypothesis

The International System of Units

We call it "The Metric System"

^{(Which is vastly superior to the Imperial or English System)}

Measurements represent quantities

A quantity is something that has magnitude, size, or amount

Special Rule of Le Systéme International d'Unités (SI Units)

• SI Units are not written with commas. So, instead of 75,000, we would write 75 000 with a space where the comma would be since other countries use a comma as a decimal point.

• (For all tests or quizzes, leave out the space and comma for numerical fill-in-the-blank questions)

Each unit has a name, a quantity it represents, and an abbreviation

IMPORTANT

"Mass" is often confused with "Weight." However, mass is how much stuff is present. Weight is a measure of the gravitational pull on matter.

Derived Units

Combinations of SI base units

6 Derived SI Units

• Area -  $length\cdot width$  or  $m^2$  

• Volume -  $length\cdot width\cdot height$  or  $m^3$  

• Density -  $\frac{mass}{volume}$  or  $\frac{kg}{m^3}$  

• Molar Mass -  $\frac{mass}{amount\ of\ matter}$  or  $\frac{kg}{mol}$  

• Molar Volume -  $\frac{volume}{amount\ of\ matter}$  or  $\frac{m^3}{mol}$  

• Energy -  $force\cdot length$  or  $N\cdot m$  

Converting from one unit to another

In order to convert from one unit to another, we must learn and use conversion factors

Conversion factors of SI Units are multiples of 10

Each prefix has a fixed ratio with the base unit, meaning that if we memorize the ratio, we can easily convert by moving the decimal point around.

Common SI Unit Prefixes include:

• "Kilo-" - 1 000 of the base unit

• "Centi-" - 1/100 of the base unit

• "Milli-" - 1/1 000 of the base unit

These two rules help us convert quickly:

• If we are converting from a smaller unit to a larger unit, we divide by the conversion factor.

• If we are converting from a larger unit to a smaller unit, we multiply by the conversion factor.

• i.e. Converting from 2.4 meters to centimeters means we multiply by the conversion factor of 100. Thus, 2.4 meters = 240 centimeters.

Conversion factors of the previous common prefixes are...

• "Kilo-" - multiply or divide by 1 000

• "Centi-" - multiply or divide by 100

• "Milli-" - multiply or divide by 1 000