Example : Designing an Experiment
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.
1. 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?
I found a website 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?
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?
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?
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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