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The Scientific Method
Unit Notes
The Scientific Method is a set of steps taken to solve a problem or answer a question. The number of steps and the task at each step can vary, depending on the source (book or person) you use, but the important thing to realize is that there is a logical order followed. [For example, you can’t analyze the data before you’ve collected it, and you can’t collect data before you’ve designed the experiment.]
Steps of the Scientific Method:
- Identify question or problem
- Make observations
- Develop a hypothesis
- Design the experiment (to test your hypothesis)
- Do the experiment and collect data
- Analyze data and draw conclusions
- Communicate your results
Ê Question or Problem
This should be something that can be scientifically tested, not based on opinion. (For opinion-type questions, surveys are used instead of scientific experiments.) Ex/ a. Will my plant grow better on the south side of my house or the north side? b. What amount of study time will give me the best test grades? c. Does the amount of sleep I get have an effect on my basketball game performance?
Ê Observations and Inferences
An observation is the use of any of your five senses (touching, tasting, seeing, hearing, smelling) to find out something about your environment (your environment could be your house, bedroom, classroom, etc.).
Because our senses are limited, we sometimes use instruments to help us make better observations. EX/ Using a ruler to determine the exact length of a table Using a microscope to see cells Using a hearing aid to distinguish between bird songs
Mass: the amount of matter in an object, measured in grams Volume: the amount of space an object takes up, measured in milliliters or cubic centimeters Weight: the gravitational pull on an object, varies with distance from the center of the Earth, measured in Newtons Density: the amount of matter in a given amount of space (mass divided by volume), measured in g/mL or g/cm^3
Measuring allows us to make detailed, accurate observations. In science, we always measure using the metric system.
Metric prefixes: Kilo = 1000. *Hecto = 100. *these prefixes are *Deka = 10. rarely used (standard) = 1. *Deci = 0. Centi = 0. Milli = 0.
To convert measurements within the metric system, you can either set up a mathematical proportion and cross multiply, or use the “metric number line.”
kg gram cg mg km meter cm mm kL liter cL mL
Rule: Always go from what you know to what you don’t know, and countspaces (not lines!). Move the
decimal that many places in that direction.
EX/ How many grams are in 47 kilograms? To go from kilograms (what you know) to grams (what you don’t know), you move 3 spaces to the left. In the number “47” the decimal is at the end, so move it 3 spaces to the left. Fill in empty spaces with zeroes. The answer is 0.047 grams. (the zero in front of the decimal doesn’t matter)
Practice:
- How many liters are in 2.96 milliliters? (0.00296 L)
- 44 meters is equal to how many centimeters? (4400 cm)
- If you walked 65,028.0 millimeters, how many kilometers would that be? (0.065028 km)
Sometimes it is necessary to organize our observations in a more meaningful way. This is called classification. Things are classified based on similarities among properties of objects.
Once a lot of observations have been made, you can draw conclusions from them. This is called an inference. [Think of it this way: observations are generally facts; inferences are generally guesses.]
Independent or Manipulated variable: the “cause”; the thing that is changing or being manipulated in the experiment Dependent or Responding variable: the “effect”; the thing that is the result of the independent variable
EX/ If I were to carry out an experiment to determine if my study time really improves my test scores, the actual thing I’d be changing is the amount of time I study, so that would be the independent variable. This should affect my test scores, therefore my test scores are the dependent variable. (The test score
depends on how much I study….try to figure out which one causes the other to happen.)
[Hint: In many scientific experiments, “time” is an independent variable. There may be two independent variables, with time being one of them. For example, even though you may be feeding the plants different foods, time is increasing as the experiment continues also.]
Ê Perform the experiment and collect data
If we were to carry out the experiment in the above example, we would make sure that all the variables are controlled except the plant food. This means we would use the same type of plant in the same type of pot with the same type of soil and place them in the same location with the same amount of water and sunlight and temperature. We would give them the same amount of food (just two different types) at the same times for the same number of days. We would make observations by periodically checking for color changes, number of blossoms, and measure the height of the plant for growth.
In most scientific investigations, data is collected in the form of a table. If this is the case, the independent variable should be listed on the left side; the dependent variable on the right side.
Ê Analyze and Conclude
At the end of the experiment you examine your data and observations and look for a pattern. You are trying to determine what the relationship is between your independent and dependent variables. The following are the most common relationships:
Direct relationship: As one variable goes up, the other goes up also. And, as one variable goes down, the
other goes down also. [On a line graph, the line goesup from left to right.]
EX/ Amount of practice shooting hoops and points scored in a game generally have a direct relationship: the more you practice, the more points you should have.
Inverse relationship: As one variable goes up, the other goes down. [On a line graph, the line goesdown
from left to right.] EX/ Amount of drugs you do and the number of brain cells you have. The more drugs you do, the fewer brain cells you have.
Constant relationship: As one variable changes, the other is unaffected. [On a line graph, this is either a straight horizontal or vertical line.] EX/ Time and location of classroom desks. As the days go on, the desks in the classroom stay in the same place. There is no relationship between the two variables.
Quite often, it is useful to put the data in the form of a graph so it can be understood better.
[Hint: It is extremely rare to use bar graphs or pie graphs in science. It will almost always be a line graph.]
Rules for Making Graphs:
- Pencil only!
- Use a straight-edge to draw each axis.
- The independent variable goes on the horizontal (X) axis. The dependent variable goes on the vertical (Y) axis.
- You must label the units on each axis! This tells the reader what the numbers represent. [If your horizontal axis is labeled “TIME,” you must put the unit in parentheses (hours, days, years, etc.)]
- Lines must be smooth and solid and should not be thicker than the points they’re connecting. [Although a “best-fit” line is acceptable, we prefer a point-to-point line.]
- Use an appropriate scale for each axis -- every space along that axis is worth the same amount. x If your data includes a zero, it MUST be at the origin of your graph (unless you also have negative numbers) x Use a scrunch sign only if you must and use it only at the origin and if you don’t have a zero in your data
- All data must fit on the graph scale. If it doesn’t fit, choose a more appropriate scale.
- The graph should make the best use of all available space (it should not be crammed into a quarter of the piece of paper).
- The title must include both variables.
Ê Communicate your results
In the science classroom, you will communicate your results in the form of a lab report. Scientists often publish their results in journals so that other scientists can benefit from their research. Although it is not part of the scientific method, it is also necessary to repeat your experiment at least one more time, if not several, to make sure of the results.
