Scientific Models: Information Sheet for Students
From:
http://teachers.oregon.k12.wi.us/sundstrom/Physical%20Science/Measu
rement/Scientific%20Modeling%20Reading.pdf
What is a scientific model?
• Models are ideas that scientists use to explain patterns they observe in the
world.
• Models are judged to be acceptable or not based on how well they can
explain and predict data and how consistent they are with what is already
known about the world.
• Models are constantly being used to ask more questions about the world
and when new data are gathered, models are revised or discarded altogether.
Scientific knowledge is not static, but is always changing.
Throughout this semester, you will be making observations and looking at
how evidence or data are connected. Explanations will be made from these
patterns of data, and the explanations will be tested by talking through them
and thinking about what makes sense. The story that makes the most sense
will be your theory or model for what happened. This process – making
observations, identifying patterns in data, and developing and testing
explanations for those patterns – is quite similar to what scientists do as they
develop explanations for natural phenomena. Such explanations are called
scientific models. Scientists use drawings, graphs, equations, three
dimensional structures, or words to communicate their models (which are
ideas and not physical objects) to others. For example, a scientist might use
3-dimensional balls and sticks to help her communicate her ideas or model
about molecular structure. Galileo developed a model to explain the patterns
in the movements of objects in the sky, including the rising and setting of
both the sun and moon. Currently, scientists are developing models to
explain the phenomenon of uncontrolled cell division (or lack of “apoptosis”
which is programmed cell death) associated with cancer. There are countless
other important models already accepted by scientists and as many others
that are currently being developed.
Why is scientific modeling important?
Most children like to play with models, including model cars, tinker toys,
model houses, and so on. Likewise, most scientists interact with models.
However, their model interaction is out of necessity (and maybe a bit of their
childhood left in them!), as the forging of new science is frequently
dependent on the development of models. Many times the system or object
of a scientist’s interest may be too small to be observed directly, like parts of
atoms. Other objects may be inaccessible for direct visual study, like the
center of the Earth or the surface of a distant galactic object. Other topics of
study, such as gravity, magnetism, or thermodynamics, can be studied
through their effects on matter. Because gravity, magnetism, and energy
cannot be seen directly, they are also modeled. So a scientific model can be
a scaled-down version or a scaled-up version of a natural object or system.
New scientific discoveries and understanding frequently depend upon
scientists developing scientific models and interacting with them.
Types of scientific models
Scientists develop models in many different forms. Models may be actual
physical constructions of mental images. They can also be mathematical
models. cA model of the Earth, moon and sun, using wooden spheres that
move mechanically, can physically model the phases of the moon and
eclipses. The mental models of early scientists pictured the atom as a solar
system in which the sun modeled the nucleus and orbiting planets
represented the electrons. Others models may be mathematical in nature.
Rays of light can be treated as waves and equations can be developed that
graphically describe the properties of those waves in great detail.
How do you decide whether a model is "right"?
A community of scientists may have more than one model to explain a given
phenomenon. Models are judged based on a number of factors:
• Can the model explain all or most of the observations?
• Can the model be used to predict the happenings of the system or event if it
is manipulated in a specific way? For example, if a new piece of evidence is
found, will your model still be the most likely story of what happened?
Being able to correctly predict experimental outcomes is a powerful way of
testing some kinds of models.
• Is the model consistent with other ideas we have about how the world
works? Any models involving an invisible alien man who can do magic are
automatically rejected on the basis of their absurdity: it is not realistic or
plausible for such things to happen — even if it explains all the data.
Getting back to the question, "which model is right?" we have two important
points to make: first, scientists don’t ask whether an answer is "right". They
ask whether a model is "acceptable". And acceptability is based on a
model’s ability to do the three things outlined above: explain, predict, and
be consistent with other knowledge. Second, more than one model may be an
acceptable explanation for the same phenomenon. It is not always possible
to exclude all but one model — and also not always desirable. For example,
physicists think about light as being wavelike or particle-like and each
model of light’s behavior is used to think about and account for phenomena
differently.
Do models ever change?
Absolutely!!! Your models for what is happening to produce the data
patterns you see may change from one day to the next. As groups share ideas
and new experiments produce new observations, the models you accept are
often replaced or modified. The modified models are more acceptable to you
because they are able to explain more data, are better able to be used to
predict experimental outcomes, or are more consistent with other ideas.
Historically, many scientific models have changed a great deal in light of
new data and new ideas. For example, at one time scientists thought that
human sperm contained a tiny, pre-formed person (a "homunculus") and that
the human egg was mainly a source of food for the developing organism.
When more advanced microscopes made closer observations of sperm and
egg possible, this model was discarded. The current model — in which both
egg and sperm contribute DNA to the future organism —is better able to
explain the fact that organisms inherit characteristics of both parents as well
as observations of cellular mitosis.
Summary Questions:
1) In YOUR OWN WORDS write a few sentences describing what a
scientific model is.
2) What are some important things a scientist looks for when she is judging
the acceptability of a model?
(Describe AT LEAST THREE.)
3) Give an example of a once-accepted model that was replaced by a revised
model. Describe SPECIFICALLY why the model was replaced and why the
new model is considered to be better than the old one (you may use an
example from the article, from the modeling activity you did in class, or
from another area of science).
Adopted
from:
http://www.wcer.wisc.edu/ncisla/muse/earth-moonsun/materials/intro/material1D/activities/modelsHW.html
From:
http://en.wikibooks.org/wiki/High_School_Earth_Science/Nature_of_Scienc
Three Types of Scientific Models
Many scientists use models to understand and explain ideas. Models are
representations of objects or systems. Models are often very useful because
they are more practical and simpler than the real life object. They may be
manipulated and adjusted more easily. There are three types of models and
each type is useful in certain ways. Each has drawbacks as well.
Physical Models
Physical models are physical representations of whatever subject is being
studied. These models may be simplified by leaving out certain real
components, but will contain the important elements. Model cars and toy
dinosaurs are examples of physical models. Drawings and maps are also
physical models. They allow us to see and feel and move them, so that we
can compare them to one another and illustrate certain features.
We can use a drawing to model the layers of the Earth (Figure 1.5). This
type of model is useful in understanding the composition of the Earth, the
relative temperatures within the Earth, and the changing densities of the
Earth beneath the surface. Yet there are many differences between a cutaway model of the Earth and the real thing. First of all, the size is much
different. It is difficult to understand the size of the Earth by looking at a
simple drawing. You can’t get a good idea of the movement of substances
beneath the surface by looking at a drawing that does not move. The model
is very useful but has its shortcomings.
Figure 1.5: The Earth's Center
Conceptual Models
Figure 1.6: A collision showing a meteor striking the Earth.
A conceptual model is not a physical model, but rather a mental explanation
that ties together many ideas to attempt to explain something. A conceptual
model tries to combine knowledge and must incorporate new knowledge that
may change it as knowledge is acquired. The origin of the moon, for
example, is explained by some as a Mars sized planet that hit the Earth and
formed a great cloud of debris and gas (Figure 1.6). This debris and gas
eventually formed a single spherical body called the Moon. This is a useful
model of an event that probably occurred billions of years ago. It
incorporates many ideas about the craters and volcanoes on the Moon, and
the similarity of some elements on both the moon and the Earth. Not all data
may fit this model, however, and there may be much information that we
simply don’t know. Some people think that the Moon was initially an
asteroid out in space which was captured in orbit by the gravity of the Earth.
This may be a competing conceptual model which has its own arguments
and weaknesses. As with physical models, all conceptual models have
limitations.
Mathematical Models
A third type of model is the mathematical model. These models are created
through a great deal of consideration and analysis of data. A mathematical
model is an equation or formula that takes many factors or variables into
account. These models may help predict complex events like tornadoes and
climate change. In order to predict climate change, for example, a
mathematical model may take into account factors such as temperature
readings, ice density, snow fall, and humidity. These data may be plugged
into equations to give a prediction. As with other models, not all factors can
be accounted for, so that the mathematical model may not work perfectly.
This may yield false alarms or prediction failures. No model is without its
limitations.
Models are a useful tool in science. They allow us to efficiently demonstrate
ideas and create hypotheses. They give us visual or conceptual manners for
thinking about things. They allow us to make predictions and conduct
experiments without all of the difficulties of real-life objects. Could you
imagine trying to explain a plant cell by only using a real plant cell or trying
to predict the next alignment of planets by only looking at them? In general,
models have limitations that should be taken into consideration before any
prediction is believed or any conclusion seen as fact.