Where do scientific experiments
come from?
In some labs, you will be given a scientific problem to solve by designing
your own experiment. If that is the case, go on to PreLab Question #1
(below). But if you have been asked to come up with your own scientific
problem, you need to do some thinking before beginning to answer the PreLab
questions:
A scientific problem
is something you don’t understand but you can do an experiment to
help you understand. Scientific problems are usually based on observation
of scientific phenomena. Here is some advice to help you identify a scientific
problem you can address by designing your own experiment.
1) Find a topic:
A topic is a relatively
specific area of knowledge, or subject, you will be working in, such as
smoking and lung cancer, sexual selection in birds, gravity, Newton's
Laws of Motion, properties of water, etc... If you have been given a topic,
you may need to narrow it, to identify a more specific topic within the
broader one. This can make it easier to work with. If you are supposed
to choose your own topic, do some brainstorming about things you have
learned about in your science course that was particularly interesting
for you, something you’d like to know more about. Write down some
possible topics and choose the one that seems most interesting to you.
2) Identify a problem within the topic:
The problem is something
you’d like to know more about, a question you’d like to answer.
Questions can come from many different sources: from lectures or textbooks,
from an experiment you have done that raised other questions, from articles
you’ve read in scientific journals or even newspapers and magazines.
To identify a scientific problem, then, you can find sources that relate
to your topic and look to see what problems are raised in your search.
Write down the problems that you find. Choose one that would be interesting
to solve and that is feasible for you to solve. Now you are ready to answer
the following PreLab questions:
PreLab: questions to answer before doing the lab
1.
What is the problem? Describe the problem in your own words. Be sure
that your description includes known factors (information about
the problem given to you in the lab in a problem statement, for example)
and unknowns (what you need to find out in order to solve the problem).
Then restate the problem in the form of a question or questions that will
guide your research.
Example:
Background
for the experiment:
Lori is on her school's volleyball team. Because she and her teammates
spend a lot of time doing jumping exercises, she has become interested
in the standing vertical leap, which plays an important role not only
in volleyball but also in basketball. Lori knows that success in both
sports depends to a large extent on an athlete's ability to jump higher
than opposing players. She wants to design an experiment in biomechanics
that will help her determine what jumping strategies athletes can use
to jump their highest.
What
is the problem?
The standing vertical jump plays a critical role in several sports,
especially volleyball and basketball. In volleyball, players must spike
the ball and block spikes by the opposing team by leaping from a standing
position. In basketball, players often shoot under the basket and rebound
from a standing position. In both sports, the effectiveness of the players
can be increased by being able to jump higher. The problem, though,
is that many players don’t know how to make the best use of biomechanics
to jump their highest. This is an experiment that I hope will provide
information that can help athletes, including myself, jump higher.
What I know is that there are, generally speaking, two approaches to
vertical jumps from a standing position. The first is called the squat
jump. You begin the jump in a modified crouch or squat with the knees
bent and then spring from that position. In the other approach to jumping,
you begin the jump with a downward movement of the body and arms that
leads to an upward spring. The unknown is which of these two approaches
allows the jumper to jump higher.
My question is: Which of these two approaches to the vertical standing
jump, the squat jump and the countermovement jump, provides the biomechanics
that result in a higher jump?
2.
What do you know about the science of the problem that could help you
answer your research question? State the scientific
concept (see below for definition) that the lab is about (something
like the quantization of energy, photosynthesis, or momentum conservation).
Write down information you can find about the concept that might be useful
in answering your research question (check lab manual, textbook, class
notes, handouts, etc.). Note any citations of sources you use. Go to Citations
and References under Resources of the web version of this document
for more help.
Scientific
Concept:
Most science labs are designed to help you learn about a scientific
concept. If you are having trouble identifying the scientific concept
this lab is about, check the title of the lab in the lab manual and
read the introduction to the lab in the manual. It will be something
like photosynthesis, quantization of energy, or momentum conservation.
Write down the scientific
concept. Then write down what you know about the concept based on the
lab manual, textbook, class notes, and handouts. Don’t try to
make it pretty; just keep writing. Get as much down as you can. Because
the point of the lab is to learn about the scientific concept, it’s
important to state what you already know.
Example:
What
do you know about the science of the problem that could help you answer
your research question?
I found a web site and an article that helps me to understand the standing
vertical jump. The scientific concept involved in understanding the
standing vertical jump is Newton’s third law of motion: for every action,
there is an equal and opposite reaction. Basically, when a person jumps,
she is overcoming her body weight, the force of gravity that holds her
on the ground. The jumper applies force against the surface she is jumping
from and that force results in the equal and opposite reaction of resisting
gravity by elevating off the jumping surface.
Thus, the height of a jump may be understood in terms how much force
is exerted against the jumping surface. Height is a function of acceleration,
velocity, and time: how much time the jumper is in the air depends on
the acceleration and speed of the jump. The greater the force against
the jumping surface, the greater the acceleration and velocity of the
jump and the longer the jumper is in the air. The length of time in
the air correlates to the height of the jump—“hang time.” Thus, acceleration/velocity/time
are key to the height of the jump. What this scientific concept suggests
is that the biomechanics of a jumper that allow the jumper to apply
the greatest force against the jumping surface will lead to the highest
jump.
3.
What is your hypothesis for the answer to your research question?
Using what you know about the problem and the scientific concept of the
lab, state a hypothesis
(see below for definition), your best estimation of the answer to your
research question. Then describe the reasoning that led you to your hypothesis,
using what you know about the scientific concept as a basis for your reasoning.
Hypothesis:
A hypothesis
is a scientist's best estimation, based on scientific knowledge and
assumptions, of the results of an experiment. It usually describes the
anticipated relationship among variables in an experiment. Since dependent
variables "depend" on independent variables, there has to
be a relationship between the two. The anticipated relationship between
the dependent and independent variables is the result you expect when
one variable reacts with another.
A hypothesis typically
leads to the crucial questions that must be addressed in the lab report:
did you find what you expected to find? why or why not? The point of
an experiment is to test the hypothesis. Write or sketch your hypothesis,
describing the relationship among the variables you listed .
Example:
What
is your hypothesis for the answer to your research question?
I hypothesize that the countermovement jumps will be higher than jumps
from the squat position. I further hypothesize that the faster the downward
countermovement of the jump the higher the jump. The reasoning behind
these hypotheses comes out of Newton’s third law of motion. If for every
action there is an equal and opposite reaction, then it is reasonable
to expect that the more force that is exerted against the jumping surface
the higher the jump. And the downward movement preceding the actual
jump would apply more force against the jumping surface than simply
jumping, like a wound up spring, from a squat position.
It is also logical that more rapid countermovements will put more force
on the jumping surface and thus will lead to higher jumps. Generally
speaking, then, the greater the force a jumper can apply against the
jumping surface, the greater the acceleration and velocity of the resulting
jump, the more time the jumper is in the air, and, therefore, the higher
the jump.
4.
What variables can you use to test your hypothesis? A well-designed
experiment needs to have variables.
Look over your hypothesis, and identify the variables that you will be
testing during your experiment: what you can measure or observe (dependent
variables) and what you can manipulate in an experiment for the measurements
or observations (independent
variables). List your variables. Then describe, in words or in
a sketch, the relationship among the variables as predicted by the
hypothesis. (See below for definitions of underlined terms.)
Variables:
A variable
is what is measured or manipulated in an experiment. Variables provide
the means by which scientists structure their observations. Identifying
the variables in an experiment provides a solid understanding of the
experiment and what the key findings in the experiment are going to
be.
To identify the
variables, read the lab procedure described in the lab manual. Determine
what you will be measuring and what you will be manipulating for each
measurement. The value(s) you are manipulating is called the independent
variable (see definition below) and the value(s) you are observing/recording
is called the dependent variable (see definition below). Write down
the dependent and independent variables.In more advanced labs, you may
have multiple variables (see definition below), more than one independent
and dependent variable.
Multiple
Variables:
It is possible to have experiments in which you have multiple variables.
There may be more than one dependent variable and/or independent variable.
This is especially true if you are conducting an experiment with multiple
stages or sets of procedures. In these experiments, there may be more
than one set of measurements with different variables.
Example: You are
interested in finding out which color, type, and smell of flowers are
preferred by butterflies for pollination. You randomly choose an area
you know to be inhabited by butterflies and note all the species of
flowers in that area. You want to measure pollination of flowers by
butterflies, so your dependent variable is pollination by butterflies.
The independent variables are flower color, type, and smell. You will
need to specify relationships for each of these independent variables
with the dependent variable.
Dependent Variable:
A dependent variable is what you measure in the experiment and what
is affected during the experiment. The dependent variable responds to
the independent variable. It is called dependent because it "depends"
on the independent variable. In a scientific experiment, you cannot
have a dependent variable without an independent variable.
Example: You are
interested in how stress affects heart rate in humans. Your independent
variable would be the stress and the dependent variable would be the
heart rate. You can directly manipulate stress levels in your human
subjects and measure how those stress levels change heart rate.
Independent
Variable:
An independent variable
is the variable you have control over, what you can choose and manipulate.
It is usually what you think will affect the dependent variable. In
some cases, you may not be able to manipulate the independent variable.
It may be something that is already there and is fixed, something you
would like to evaluate with respect to how it affects something else,
the dependent variable like color, kind, time.
Example: You are
interested in how stress affects heart rate in humans. Your independent
variable would be the stress and the dependent variable would be the
heart rate. You can directly manipulate stress levels in your human
subjects and measure how those stress levels change heart rate.
Example:
What variables
can you use to test your hypothesis?
Because I have two hypotheses, I need two sets of independent and dependent
variables. For the first hypothesis (that the countermovement jumps
will be higher than squat jumps), my independent variable will be the
two different approaches to the biomechanics of jumping, the countermovement
jump and the squat jump. These are independent variables because I will
be able to manipulate them in my experiment. My dependent variables,
what I will be measuring in the experiment, will be the heights of jumps
by the subjects in my experiment.
For my second hypothesis (that the faster the countermovement the higher
the jump), my independent variable will be the different downward speeds
my subjects will use as they jump. The dependent variables will be the
different heights of these jumps by the subjects in this experiment.
5.
What experiment(s) could you use to test your hypothesis? Referring
to the list of variables, brainstorm some experiments you could do that
would allow you to manipulate variables so that you can make the measurements
or observations necessary for testing the hypothesis.Your experiment may
require control
and treatment groups (see below for definition). Choose the experiment
most likely to yield the results you need to test your hypothesis. List
the materials and outline the methods you will use for your experiment.
(Remember that you have to work with the materials and lab instruments
available to you.)
Control
and Treatment Groups:
A control group is used as a baseline measure. The control group is
identical to all other items or subjects that you are examining with
the exception that it does not receive the treatment or the experimental
manipulation that the treatment group receives. For example, when examining
test tubes for catalytic reactions of enzymes when added to a specific
substrate, the control test tube would be identical to all other test
tubes with the exception of lacking the enzyme. The treatment group
is the item or subject that is manipulated. In our example, all other
test tubes containing enzyme would be part of the treatment group.
Example:
What
experiment(s) could you use to test your hypothesis?
Experiment #1. I will use 6 players
from my volleyball team. I will begin by training the players in the
two approaches to jumping biomechanics, giving them opportunities to
practice each approach. Then each player will make a series of five
paired jumps related to the independent variable. Three players will
do pairs consisting first of a squat jump and then a countermovement
jump. The three other players will have the opposing pairing, first
countermovement jump and then squat jump. (This is to be sure that fatigue
doesn’t affect the results.) The players will make their jumps in a
standard set up used for jumping exercises: a suspended board with measurement
lines marked on it that players will touch at the height of their jump.
I will record the height of each of the jumps.
Materials needed: vertical jump measurement set-up
Experiment #2. I will use the same
6 players. I will ask each one to make five countermovement jumps, each
jump in the series consisting of a downward thrust of a different speed,
which I will measure according to the time it takes. I will train the
players to jump to a number count from the moment they begin the downward
movement to the point their feet leave the jumping surface. Half the
players will start with a slow downward movement, the first to a count
of 5, second 4, and so on to a quick count of 1. The other half will
proceed from fast to slow. In order to make more accurate measurements
of the speed of the countermovements, I will videotape the jumps and
time each of them (from the beginning of the downward movement to the
point the feet are off the surface) with a stopwatch while viewing the
video later. I will record the height of each of the 5 jumps in the
series.
Materials needed: vertical jump measurement set-up; camcorder; stopwatch;
VCR.
References
Linthorne, Nick. "Standing Vertical Jump."
http://www.brunel.ac.uk/~spstnpl/BiomechanicsAthletics/VirticalJumping.html
(3 January 2004).
Linthorne, Nicholas P. "Analysis of standing vertical jumps using a force
platform."
American Journal of Physics 69 (2001): 1198-1204.
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