# uniform circular motion

Discussion in 'Physics' started by ronn, Nov 6, 2009.

1. ### ronn Thread Starter Member

Nov 1, 2007
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Hi Everyone,
In a uniform circular motion, the acceleration and net force is towards the center, but why does the object dont go to the center if it is accelerating in that direction?
thanks,
Ron

2. ### mik3 Senior Member

Feb 4, 2008
4,846
68
The force is towards the center because the object moving tends to escape from its circular orbit due to its inertia. This force towards the center is the force which keep the object rotating.

3. ### Papabravo Expert

Feb 24, 2006
11,595
2,422
The Zen answer is -- it is all about the balance of forces in the universe.

Nov 9, 2007
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5. ### KL7AJ AAC Fanatic!

Nov 4, 2008
2,165
398

This is precisely analogous to energy storage in an CL circuit. The acceleration force (EMF) is always at right angles to the current flow (ELI the ICE man) so no energy is dissipated. It's all imaginary!

(Actually, I think imaginary is an unfortunate term, but it's ingrained in our math)

Eric

6. ### Papabravo Expert

Feb 24, 2006
11,595
2,422
It came from pondering the solution to the algebraic equation
Code ( (Unknown Language)):
1.
2. x^2 + 1 = 0
3.
which has no solution in the domain of real numbers. What would you call it instead, assuming you knew nothing about electrical engineering?

7. ### KL7AJ AAC Fanatic!

Nov 4, 2008
2,165
398

Probably nothing, since I didn't understand imaginary numbers at all until I started playing around with R.F.!

8. ### KL7AJ AAC Fanatic!

Nov 4, 2008
2,165
398

However, I have given the matter some thought over the years. The problem I have with "imaginary" is the subtle implication that such numbers have less of a physical implcation than "real" numbers, which we know is far from the truth. The first time I got knocked on my keister playing with an ignition coil, the "reality" of this "imaginary" reactance was driven home quite soundly!

Maybe our collective brainpower on AAC might come up with a better term than Imaginary! We could all become famous!

Eric

9. ### Papabravo Expert

Feb 24, 2006
11,595
2,422
Again with the "legends in our own minds" theme. Ahh...cha...cha...cha

10. ### hgmjr Moderator

Jan 28, 2005
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An interesting application of this phenomenon is its ability to permit the calculation of the approximate altitude above the earth that a satellite is likely to be in order to remain in geo-stationary orbit.

11. ### KL7AJ AAC Fanatic!

Nov 4, 2008
2,165
398

Interestingly, this assumes the Earth to be a point source of gravity....a pinhead with the mass of the Earth. Actually LOCAL perterbations of gravity can have significant effects, creating "bumps" in the normal elliptical orbital path. When I worked for the phone company, we had to do a small amount of satellite tracking....I'm glad someone ELSE had to figure out the bumpy data for us!

Eric

12. ### hgmjr Moderator

Jan 28, 2005
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You're right about the variation in gravity. I was mainly interested in showing that the altitude could be estimated using the principle of circular motion.

hgmjr

13. ### BillO Distinguished Member

Nov 24, 2008
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Last edited: Nov 14, 2009