Notes: The Nature of Science
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What is Science?
The goal of science is to investigate and understand nature, to explain
events in nature, and to use those explanations to make useful predictions.
Science differs from other human endeavors in several ways:
1)
Science deals with the natural world.
2) Scientists collect and organize information in a careful, orderly
way,
looking for patterns and connections between events.
3)
Scientists propose explanations that can be tested by examining
evidence.
Evidence Is Based on Observation
Science investigations start with observations.
Observation involves using one or more of the senses (sight, hearing, taste,
touch, smell) to gather information. The information gathered through
observation is called data.
Observations can be classified into 2 types:
1) Quantitative: involving numbers (like counting or measuring
objects)
2)
or
Qualitative: involve characteristics that cannot be easily measured
counted.
It is important for a scientist to be objective and avoid bias (such as
personal opinion) when making observations.
Interpreting Evidence
Observations are often followed by inferences. An inference is a logical
interpretation of data. The inferences made by a person are based on his or
her prior knowledge and experience.
Explaining the Evidence
When enough data is gathered, a hypothesis can be made. A hypothesis is
a possible explanation for a set of observations or an answer to a scientific
problem.
•
A hypothesis may arise from prior knowledge, logical inferences, or
imaginative guesses.
•
A hypothesis is useful only if it can be tested.
•
Testing the hypothesis can be done by making further observations or
through careful questioning.
•
The results of testing may support the hypothesis, suggest that it is
only partly true, or prove that the hypothesis is wrong.
•
A tested hypothesis is valuable to scientists because it helps to
advance scientific knowledge.
How Scientists Work
To solve a problem, a scientist follows a specific plan.
1)
First, she/he states the problem. A problem cannot be solved until
you know exactly what it is.
2)
Once the problem is described, the scientist forms a hypothesis, a
possible solution to the problem. The simplest solution is often the
best solution!
3)
A
his
controlled experiment can give a sicentist more information about
or her hypothesis. The factors in the experiment that change are
called variables.
•
It is best to set up an experiment in which only one variable is
being tested. All other variables should be unchanging, or
controlled. This would be a controlled experiment.
•
The variable that is deliberately changed is called the
manipulating (or independent) variable.
•
The variable that is observed and that changes in response to the
manipulated variable is called the responding (or dependent)
variable.
Results are Recorded and Analyzed:
4)
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Next, a scientist may want to perform a controlled experiment.
Observations can be written descriptions of events you noticed during
an experiment or problems encountered. Keep careful notes of
everything you do and everything that happens. Observations are
valuable when drawing conclusions, and useful for locating
experimental errors.
•
5)
Analysis involves interpreting results and explaining why the
results came out as they did
When results are in, a scientist can then draw a conclusion.
◦
Scientists use the data from an experiment to evaluate the hypothesis
and draw a conclusion. They use the evidence to determine if the
hypothesis was supported or refuted.
◦
It is important to remember that the scientific method is NOT a rigid set
of rules, but rather a framework for investigating a problem. The order of
steps may be altered, and the experiment may certainly be repeated
many times before reaching a conclusion.
◦
The data that are collected using the scientific method become part of
the body of scientific knowledge. The hierarchy of scientfic knowledge
can be described as follows:
problem-->hypothesis--> theory
6) A hypothesis that is supported by experimental observations may become part
of a
theory, which is an explanation of scientific phenomena. Profound theories
describing important scientific concepts may become scientific laws, or
principles.
The Scientific Method in Action
1) Early scientists wanted to know how new organisms came into being. (They stated
this as their problem or question to be solved: "How do new organisms come into
being?")
2) At the time, people believed that organisms suddenly appeared from nonliving
matter. (Ex. maggots from meat, mice from grain) This idea was called spontaneous
generation (life could arise from nonliving matter).
3) In 1668, Francesco Redi proposed a different hypothesis about the appearance of
maggots. He thought that flies laid eggs on the meat, but the eggs were just too small
for people to see He thought that the eggs then developed into maggots.
4) Redi predicted that keeping flies away from meat would prevent the appearance of
maggots. Redi set up an experiment in which he controlled all the variables-expect one.
He put meat in two jars. Redi left one jar of meat open so that flies could enter, and he
covered the mouth of the other jar of meat with gauze.
To read about the work of Redi, a scientist who helped disprove the theory of
spontaneous generation, click on the following URL OR type it in your address bar.
http://www.accessexcellence.org/RC/AB/BC/Spontaneous_Generation.html
One jar of meat was open, and the other jar of meat was covered with gauze. (Courtesy
of http://www.kent.k12.wa.us/staff/rlynch/sci_class/chap01/redi.html)
4) Redi recorded his data. He discovered that maggots appeared on the
meat in the control jar, the jar left open. No maggots appeared in the jar
covered with gauze.
5) In Redi's experiment, the results supported his hypothesis. He
therefore concluded that the maggots were indeed produced by flies. Redi's
results could be viewed not only as an explanation about maggots and files
but also disproved the hypothesis of spontaneous generation.
Publishing and Repeating Investigations:
You can find many example of scientists repeating the experiments of other
scientists to double check their findings.
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Needham tested Redi's experiment. He disagreed with Redi, and
thought that spontaneous generation could occur under the right
conditions. Needham developed his own experiment. He sealed a
bottle of broth and heated it. He thought that heat killed living
things. He found "little animals" (microbes) grew in the broth.
Needham assumed that the animals must have come from the gravy
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Spallanzani also tested Redi's findings. Spallanzani thought that
Needham was on the right track, but should have heated the jar
more. Spallanzani heated 2 jars. He sealed one, and one he didn't.
The open jar developed "little bugs" (microbes) in it and the sealed
one did not. This supported Redi's findings.
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Pasteur tested Redi's finding. Many scientists thought that Spallanzani
's experiment was unreliable because air was excluded from the jar.
Pasteur designed a flask that had a long curved neck. The flask
remained open to the air, but microbes from the air did not get
through the neck into the flask. As long as the broth was protected
from microbes, it remained free of living things. Pasteur showed that
all living things come from other living things. This new theory was
called Biogenesis.
Pasteur's curved neck flask prevented microorganisms from entering the broth through the
air.
http://en.wikipedia.org/wiki/File:Coldecygne.svg
How a Theory Develops
As evidence from numerous investigations builds up, a particular hypothesis
may become so well supported that scientists consider it a theory.
In science, the word theory means a well-tested explanation that unifies a
broad range of observations. A theory serves as a model that explains
something. A theory helps scientists to make predications about new
situations.
Tools and Procedures
Scientists need a common system of measurement so they can share and compare
data. Most scientists use the metric system when collecting data and performing
experiments. The metric system is a decimal system of measurement whose units are
based on multiples of 10.
To learn the units of the metric system, click on the following link OR type the link into
your address bar to learn more about the metric system.
http://lamar.colostate.edu/~hillger/everyday.htm
When scientists collect data, they are trying to find out if certain factors changed or
remained the same. The best way to do this is to make a graph or a data table. A
graph of the data can make a pattern much easier to recognize.
Microscopes are devices that produce magnified images of structures that are too
small to see with the unaided eye.
Light microscopes produce magnified images by focusing visible light rays.
Living and non-living things that are small enough to place underneath a lense
and thin enough for light to pass through can be observed. Disadvantage: Can
only magnify up to 1,000x due to distortion of bending light at higher powers.
1. Oculars (dual eyepieces) 2. Revolving nosepiece 3. Objective lenses
4. Coarse Adjustment 5. Fine Adjustment 6. Stage 7. Electric Light 8. Diaphragm and
condenser 9. metric measurement tool
http://upload.wikimedia.org/wikipedia/commons/3/3a/
Optical_microscope_nikon_alphaphot.jpg
Electron microscopes produce images that are enlarged up to 50,000,000 times
by using strong electromagnets to focus electrons through a vacuum.
Disadvantage: living things cannot be observed with electron microscopes
because a vacuum would be deadly.
Transmission Electron Microscope
http://en.wikipedia.org/wiki/File:Simens_numeri.jpg
Three basic types of electron microscopes:
SEM - scanning electron microscope - specimen are sprayed with a
coating of metal; can be magnified up to 50,000x
TEM - transmission electron microscope - requires extremely thin
slices usually preserved in hard plastic;
TEAM Transmission Electron Aberration-corrected Microscope - very
powerful type of TEM that can magnify up to 50,000,000 times!
TEAM image of the lattice structure of carbon atoms
http://en.wikipedia.org/wiki/File:Real_graphene.jpg
Useful Formula: Density is the mass per unit volume of an object. It is specific
property of matter that can be used to identify different materials.
DENSITY = mass/volume
3
• Example: An object having a mass of 8.40g and a volume of 4.2cm would
have a density of 2.0g/cm3.
3
3
◦ density = mass/volume = 8.4g/4.2cm = 2.0g/cm
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