Hello pantera2,
Tar_heel_v's comment notes one good explanation of yo-yo physics.
Here are two more:
"How do yo-yos work? Why do they come back up after being thrown
down?" (Answered by: Warren Davis, Ph.D.)
PhysLink.com
"Yo-Yo" [under "Physics of the Yo-Yo"]
The Physcis of Toys, by Eva Leidman (Ms. Eagle's 8th grade science
class,
blue class, Winter 2002)
http://www.geocities.com/evazleid/homre.html
It's also been a while since I learned physics, but as best I can
summarize it:
1) A yo-yo starts with gravitational potential energy.
2) As it falls, the gravitational potential energy is converted into
kinetic energy, both as linear momentum (momentum in a straight line)
and angular momentum (momentum of rotation).
3) At the end of the string, the angular momentum begins to dissipate
due to the friction between the axle and string.
4) If the person tugs on the string after the yo-yo reaches the
bottom, the axle can no longer slip within the string, and the angular
momentum of the spinning yo-yo causes the yo-yo to climb back up the
string.
5) The kinetic energy (linear momentum and angular momentum) are
converted back to gravitational momentum as the yo-yo climbs back up
the string.
There is no indication in these explanations that elastic potential
energy is part of the process. I assume that it is because a yo-yo
string is basically inelastic, in contrast to, say, a bungee cord.
Pages dealing with the similar phenomenon of bungee jumping do discuss
elastic potential energy. These pages show that you can have elastic
potential energy and gravitational potential energy simultaneously.
For example, see this explanation:
"Bungee Jumping: the bungee jumper initially has gravitational
potential energy this is converted to kinetic energy as the person
falls. However, after falling some distance the person stretches the
bungee cord and so kinetic energy is converted onto elastic potential
energy. At the bottom of the fall the person rises thus converting
elastic potential energy into both kinetic energy and gravitational
potential energy."
"Topic 5: Forces and Motion" [page 18]
Post-Primary Secondary Education (Deakin University)
http://www.deakin.edu.au/education/units/ppse/Peters_elect&forces_notes/Forces_and_Motion_Notes.doc
I hope that this information is helpful.
- justaskscott
Search terms used on Google:
"yo-yo physics"
"physics of the yo-yo"
bungee "gravitational potential energy" "kinetic energy" "elastic
potential energy" |
Clarification of Answer by
justaskscott-ga
on
24 Oct 2003 14:10 PDT
Sorry, I left out the URL for the PhysLink.com page. It is:
http://www.physlink.com/Education/AskExperts/ae18.cfm
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Request for Answer Clarification by
pantera2-ga
on
24 Oct 2003 15:19 PDT
Thank you for your response.
I believe that there are still a few things missing. My question
contained the sentence "Please take into consideration the energy that
must take place within the body to begin the movement." What energy
comes from the body to start the process? Your hand moves - where
does the energy come from? Chemical and or mechanical? In short, what
energy must come from the body to start the process and continue the
process?
In regard to the elasticity, I realize that it may be a very small
amount; however, is there a slight presence of elastic potential
energy, similiar to that in the bungee cord? Assuming such, when might
this conversion take place? (In the step by step process)
Please take the time to enter each additional conversion into the
steps you have already posted.
Thank you for your time. We are on the right track.
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Request for Answer Clarification by
pantera2-ga
on
24 Oct 2003 19:50 PDT
In reading your response I realized that the second part to my
question was not answered. That was:
"Additionally, can you have elastic potential energy and
gravitational
potential energy simultaneously?
Looking forward to your response.
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Clarification of Answer by
justaskscott-ga
on
24 Oct 2003 20:00 PDT
The work I was doing was on a different computer than the one I'm on
now. Some time this weekend, I will have access to that computer
again, and can look at my previous research to supplement the yo-yo
physics part of the answer, as well as add the body physics part.
There is a particular page bookmarked on that computer that I know
would go part of the way towards a clarification.
Incidentally, when you said "within the body", I had thought you meant
"body" in the sense a physicist might use it, meaning a particular
mass of matter (like a yo-yo), as in the expression "celestial body".
Now that I know that you meant human body, I can find some information
about that.)
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Request for Answer Clarification by
pantera2-ga
on
25 Oct 2003 13:06 PDT
Looking foward to your response.
|
Request for Answer Clarification by
pantera2-ga
on
26 Oct 2003 07:42 PST
Still looking forward to your response to my clarifictions.
|
Clarification of Answer by
justaskscott-ga
on
26 Oct 2003 09:54 PST
I will be clarifying the answer this evening. I am grateful for your
patience; I hope that you will like the clarification at least as much
as the initial part of the answer.
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Clarification of Answer by
justaskscott-ga
on
26 Oct 2003 23:56 PST
With respect to elastic potential energy, surely you are right that
there can be a relatively small amount of it in a stretched yo-yo
string. Unless it is 100% inelastic, a yo-yo string would seem by
definition to be able to carry elastic potential energy -- when it is
stretched the tiny amount that it can be stretched.
I had endeavored to indicate in my answer that there can be elastic
potential energy and gravitational potential energy simultaneously. I
hope that the chart at the bottom of page 2 of the following document
will further illustrate that.
"Physics - Work and Energy Worksheet Solutions"
Physics 1 - Motion and Energy - summer 2002 [Evergreen State College]
http://academic.evergreen.edu/curricular/Physics1/worksheets/WorkWS.pdf
The gravitational potential energy is always decreasing, but is not
gone, as the bungee jumper (or yo-yo) falls. Meanwhile, as the cord
(or string) begins to stretch, the elastic potential energy increases.
Thus, both forms of energy can co-exist, although one decreases as
the other increases.
Finally, the charts on the first two pages of the following document
indicate the types and sources of energy in the body.
"Energy, work"
Biomechanics [University of Sydney]
http://www.personal.usyd.edu.au/~mslee/ESSwww/lee/22208/lectures/energy-work.pdf
Applied to the yo-yo, it seems that an outstretched hand holding a
yo-yo above the ground has both gravitational potential energy
(because the hand is a certain distance from the ground, which is
pulling on it with the force of gravity) and elastic potential energy
(stored in the muscles, etc., which are stretched to hold the yo-yo in
the starting position). There is also kinetic energy, to the extent
the arm and hand move. In particular, the kinetic energy would
increase when the hand lets go of the yo-yo, and when it tugs the
yo-yo to bring it back up the line.
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