Science Project

On Thu, 12 Jan, podzol wrote:

Erant wrote:
Centrifugal, or centre fleeing, force is simply the lack of centripetal
force. See it like this, you have a string with a marble on the end. If

snip snip

circular motion is the only motion where an object can be accelerated,
yet not change it's velocity. (It is always receiving an accelerating
inwards, F = ma, where F and m are a constant, and thus a is as well.)

Gilby's right: centrifugal force is a measurable phenomenon equal and
opposite to the centripetal force, that scientists use all the time
(centrifuges are an example).

No. Centrifugal force is a observed apparent effect of circular
motion, but the force itself does not exist - it is the transmission
of centripetal force that gives rise to the same effects as if
centrifugal force existed on a part of a body.

Do a free-body diagram for the body that you think is being subject to
centrifugal force, and there is no outwards acting force on it.

However, Erant is wrong to say a body undergoing circular motion is
not changing its velocity. Its speed may not change, but its
velocity (being a vector) certainly does, since the direction of
motion is continually changing. Is this context, it is not reasonable
to simplify 'velocity' to be synonymous with 'speed'.

in principle as when we feel ourselves being forced upon when he are
accellerating or slowing in an elevator.

Exactly - and that force doesn't actually exist. Your legs feel as if
something is pressing down on you. You feel heavier as the elevator
lifts you, but there is no additional downward force being applied to
you - only an upward force applied to part of you (the soles of your
feet).

regards, Ian SMith
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podzol wrote:
Gilby's right: centrifugal force is a measurable phenomenon equal and
opposite to the centripetal force, that scientists use all the time
(centrifuges are an example).



Ofcourse, I forgot to mention that every action has an equal and
opposite reaction, the marble is pulling as hard on the string as the
string is pulling on the marble. This does not mean there is
centrifugal force. If there is no centripetal force, or when the
'centrifugal' force is equal to the centripetal force, the marble will
go in a straight line. This is what happens in a centrifuge, a
centrifuge has holes in it, so at that spot, there is no centripetal
force. No centripetal force means the object (water in this case, or
uranium hexfloride gas in another) will be pushed outwards, and
continue moving in the direction of the
velocity vector. If there was such a thing as centrifugal force, the
object would be moving in the direction of the place vector.

If I'm wrong, I'd love to know how an object can turn, when the forces
acting upon it are equal, and thus the acceleration. You can test this
with a string, and a knot in the middle. Move it over the table,
pulling equally hard on each side of the string, now, pull harder on
one side then the other. Result is that the knot will deviate from it's
path. Ofcourse, this is lateral movement, not radial, but the same
principle applies.


P.S

I might have made a few mistakes in the scientific terms, but English
is my second language.


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Erant

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I think it is perfectly okay to say it is a force, knowing that it is
really a result of a number of factors that results in a force-like
effect. We could rewrite all the literature and say "centrifugal
effect" rather than centrifual force, but in any case, it is
-effectively -equal and opposite of the centripetal force and can even
be introduced into computations as such.

-Sensu strictu -, it is not a force. In forum-speak and in the spirit
of getting along, I find 'Yes, buts...' more amicable than 'No, you're
wrongs.'


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Maybe it would be less complicated to do a scientific behavioral study
on the effects of mentioning science and unicycle on a thread in a
public forum. It'd be much more interesting.


--
Trapper
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podzol wrote:
I think it is perfectly okay to say it is a force, knowing that it is
really a result of a number of factors that results in a force-like
effect. We could rewrite all the literature and say "centrifugal
effect" rather than centrifual force, but in any case, it is
-effectively -equal and opposite of the centripetal force and can even
be introduced into computations as such.

-Sensu strictu -, it is not a force. In forum-speak and in the spirit
of getting along, I find 'Yes, buts...' more amicable than 'No, you're
wrongs.'



Sorry, I didn't mean to offend you. I do realize that in some systems,
mainly non-Newtonian (For example, accelerating systems) the
centrifugal force is used as a real force to attribute movement of
object, such as when you're making a turn with your car, and you're
using the car as a reference frame, things start sliding on your
dashboard.

I do however think that this matter might be slightly sophisticated for
a science project, especially if you start bringing it things like
inertia ( I = .5M((R1)^2+(R2)^2) for a hollow cylinder (like a wheel,
which is basically a short hollow cylinder), with R1 the distance from
the center to the inside of the wheel, and R2 the distance from the
center to the outside of the wheel, both in meters, and M the weight or
mass of the wheel. Ofcourse, you're neglecting the cranks here, which
would be I = (1/3)ML^2 with M the mass of one crank, and L the length
of one crank. (All formula's courtesy of Physics for Scientists and
Engineers by Paul A. Tipler))

I also think it amazing to find so many physicists (Or at least people
who know quite a bit about it) on a non-physics forum. Maybe that'd be
a good study, amount of people with high IQs on a unicycle


--
Erant

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Erant wrote:
Maybe that'd be a good study, amount of people with high IQs on a
unicycle


I used to think the same myself until the whole slew of "Sequel to Most
Replies" threads in JC. LOL!!1!one!!1

i'll put $20 on a bell curve distribution of iqs.


--
maestro8

Those are my principles. If you don't like those, I have others. --
Groucho Marx
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I think Kyle Holmes was on a show on the discovery channel where they
actaully quantified his balance skills. If you could figure out a way
to do that, perhaps you could get 10 or 20 people to try learning, and
test exactly how much an innate sense of balance has to do with
learning to ride. A graph showing balance skill vs. learning time would
be cool. Then write up some stuff about how balance is important to
various animal species or was to the survival of early humans.

Im not sure whether you would have enough time to do this, though. It's
more of a biology thing, so if you are limited to physics it might not
work.


--
parapsycho
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parapsycho wrote:
I think Kyle Holmes was on a show on the discovery channel where they
actaully quantified his balance skills. If you could figure out a way
to do that, perhaps you could get 10 or 20 people to try learning, and
test exactly how much an innate sense of balance has to do with
learning to ride. A graph showing balance skill vs. learning time would
be cool. Then write up some stuff about how balance is important to
various animal species or was to the survival of early humans.

Im not sure whether you would have enough time to do this, though. It's
more of a biology thing, so if you are limited to physics it might not
work.




Grr. I meant Kris Holm.


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parapsycho
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Sound good, the most basic test they used was how long you can stand on
one foot with your eyes closed for, i believe an avergae male of Kris's
age can do around 45 seconds, Kris got close to two minutes i think.


--
kington99

Dave

- what a thoroughly post-modern subversion of the cycling genre -
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Erant wrote:
Sorry, I didn't mean to offend you.

.
.
.

I also think it amazing to find so many physicists (Or at least people
who know quite a bit about it) on a non-physics forum. Maybe that'd be
a good study, amount of people with high IQs on a unicycle



No offense at all. I'm not a physicist, I'm a biogeochemist who studies
soil. But I do enjoy physics.

I like to think unicyclers are a cut above the rest, too!


--
podzol

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