
#1
Feb2212, 11:05 AM

P: 259

If the net sum of forces is zero , the object moves with constant velocity.(inertial frame)
But , when this centripetal thing comes in Suppose we have only a force acting perpendicular to the motion of the body. then how does this centripetal force comes in , there are 4 fundamental forces and all other forces can be taken from these forces , but centripetal force ? which fundamental force makes centripetal force ? and why is that when a satellite revolving around a planet , acted by gravity, force is equated to mv^2/r , but that is analogous to F=ma , so there is only one force acting that is gravity so satellite should fall but it doesnt ... what is my thinking lacking ? 



#2
Feb2212, 11:27 AM

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P: 6,924

For a moving (nonzero velocity) object, you can separate any force vector into two vectors, a force in the direction of velocity (changes speed), and a force perpendicular to velocity (centripetal force  changes direction). Even if the force is always perpendicular to velocity, it can produce about just about any path (other than sharp corners). For example imagine the possible paths of a car moving on a flat plane at constant speed with only steering inputs.




#3
Feb2212, 11:30 AM

P: 259

which fundamental force causes centripetal force then?
and why does centripetal force acts radially inwards if that happens then a satellite should go down as gravity is also acting inwards and centripetal also inwards?//. 



#4
Feb2212, 11:38 AM

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P: 40,872

What is centripetal force 



#5
Feb2212, 11:39 AM

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P: 6,924

In the case of a satellite in a circular orbit, speed^{2} / r = acceleration from gravity at that distance (r) from the center of earth, so it follows a circular path. In this case the acceleration only changes the direction of velocity, without changing it's path or speed. The satellite is always accelerating towards the earth, but it's velocity perpendicular to that acceleration causes it to remain in a circular path.
If the orbit is elliptical, then most of the time gravity is not perpendicular to velocity, and speed will change, fastest when closest to earth, slowest when farthest away from earth. In a two body system, (earth and satellite as only two objects in the universe), the center of mass of the two body system doesn't accelerate. Which fundamental source is centripetal doesn't matter. In the case of a satellite in a circular orbit, it's gravity, but the force could be magnetic (a moving charged object curves perpendicular to a magnetic field), or mechanical force like a test tube in a centrifuge. 



#6
Feb2212, 11:41 AM

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#7
Feb2212, 11:44 AM

P: 692

kushan "what is my thinking lacking ?" You are thinking of a static situation. This is a dynamic case.




#8
Feb2212, 11:44 AM

P: 259

Thank you doc al and rcgldr , that helped a lot , can you give other instance in which other fundamental force causes centripetal force .
i want to know why is centripetal force acting radially inwards ? 



#9
Feb2212, 12:02 PM

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P: 6,924

Other than zero centripetal force and a straight line path, then at any point in a curved path there is a "radius of curvature", the equivalent of the radius a tiny bit of a circular arc that would correspond to the curvature of the path at that point. It's always inwards by definition, since the direction of the "radius of curvature" would be "inwards" of the curved path. 



#10
Feb2212, 02:55 PM

P: 168

It appears to me if the rotating object is tied by some physical means to the center of rotation, the force is towards the center, but if the object is not tied to the center then the force is away from the center. Water in a bucket spinning in a vertical circle, satellites are examples of latter case. 



#11
Feb2212, 03:01 PM

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P: 40,872





#12
Feb2212, 08:39 PM

P: 168

mv^{2}/r = GMm/r^{2} This equality may not be exact, but it does the job. 



#13
Feb2212, 09:12 PM

P: 24

There is a centripetal acceleration for an object that is moving along a nonstraight curved path so according to Newton second law there must be a centripetal force,which might be a component of the total force, acting on it .




#14
Feb2312, 03:31 AM

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P: 40,872

That equation is just an expression of Newton's 2nd law applied to something in a circular orbit. 



#15
Feb2312, 03:45 AM

P: 259

Hey neanderthal, yea it is little confusing for beginners like us
If you imagine two forces acting at centre , it gives you a picture of an object also moving towards centre . 



#16
Feb2312, 04:42 AM

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#17
Feb2312, 04:44 AM

P: 259

ok , when we change frame of reference how does centripetal force become centrifugal force and start to act outwards?




#18
Feb2312, 06:01 AM

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P: 40,872




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