Science Project

Re: 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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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.

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.’

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. :wink:

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 :wink:

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.

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.

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.

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!

Maybe you should do a project about cetri*al force. The discussion and arguments are here. I can just see the footnote where you identify your source of information. (1)

(1) Categories - Unicyclist.com

There are no such things as cetripetal or cetrifugal force. Centripetal forces on the other hand, do exist.

I’m no physicist either, but I study electronics. Probably closer to a physicist then a biogeochemist though, and with an unfair advantage of having a 3.6kg book next to me, called, very appropriatly “Physics”.

Re: Science Project

The issue about the (co)existence of centripetal and centrifugal force
is somewhat philosophical. My take at it is this.

Suppose that you swing a marble on a string “in a circle”(*). Suppose
that there is an observer next to you, and that his reference frame is
connected to the solid earth. He will see the marble go round in a
circle, and hence will rightly conclude that a centripetal force is
acting on the marble, accellerating it constantly so that it doesn’t
move in a straight line.

So far nothing new.

Now take another observer, a tiny one that is sitting on the marble.
His reference frame is connected to the marble and (part of) the
string. In his reference frame he is sitting still. But this is not
for absence of force! The marble surface exerts a force on him to keep
him from flying off the marble. The force that is acting outwards
(that “tries” to let him fly off) is a centrifugal force. Because the
two forces cancel out exactly, he does not accellerate at all, in his
reference frame that is.

Similarly with forces acting on someone in an elevator. Within the
reference frame of the elevator cage, these forces are real.

F = ma is still fully valid in all cases, but a is measured in metres
per second squared and without reference (!) to a reference frame this
distance in metres cannot be defined.

(*) for an observer on the sun, the marble is not describing a circle
at all, but rather a “slightly wiggly spiraling circle” or so, because
of the motion of the Earth.

Thank you for all of the informaton but I’m only in grade nine and we don’t do physics yet so I don’t really understand all of this but I’m going to get someone older to explain but keep on putting stuff it all helps.:slight_smile:
Jeff