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Question: Centripetal & centrifugal are equal in magnitude ,opposite in direction then why they are not cancel out?

(Posted by: Om S on 2010-02-23 07:37:59)

Posted by: Pearlsawme on 2010-02-23, 08:06:28

Two equal and opposite forces acting on ONE AND THE SAME body alone can cancel each other, causing the body at equilibrium. Centripetal force acts on a body [say A] which is moving in a circle. This force is supplied by some other body [say B] By Newton's third law, the body A which is moving along the circle will exert an equal but opposite force on the other body [B]. This force is the Centrifugal force .Since these forces act not on one and the same body, but on different bodies, they will not cancel each other. If we make a stone to move along a circle, by a string attached to it, we are pulling the stone to ward us, i.e. toward the center of the circle. This force acting on the stone is the centripetal force. We can feel that the stone pulls us toward it. The force supplied by the stone on us is the centrifugal force. = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = In engineering and in some times in physics, in order to simplify the mathematical equations and in particular to change the non- inertial frame of reference into an inertial frame of reference, it is needed to apply a pseudo force on the object which is moving in a circle. This pseudo force has the same magnitude but is opposite to the centripetal force, and acts on one and the same body that moves in a circular path. This makes the object to move in an inertial frame of reference. Unfortunately this force is also called centrifugal force. Hence one must be careful to distinguish the two while solving problems in dealing with circular motion. It is always better not to use the term centrifugal force for an object moving in circular path. = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =

Posted by: dremler on 2010-02-23, 07:50:13

The centripetal force is the force that keeps a body which is in circular motion.It is a force which exists in the ground frame.However if we want to we can visualise the motion in the frame of the body in circular motion.However since the body is in circular motion it is being accelerated. Whenever we use a frame of reference that is being accelerated we have to include a force that does not exist,i.e a pseudo force.This pseudo force acts in a direction opposite to the real force(centripetal force in this case). In circular motion if we view the motion in the frame of the body,the pseudo force is the centrifugal force.The forces don't cancel out because they exist in different frames of reference.

Posted by: Robert on 2010-02-23, 08:09:07

As Dremier said. The forces don't exist in the same diagram. Centrifugal force doesn't even exist unless you are doing physics in an accelerated reference frame (for example your camera is following someone on an amusement park ride, whipping around in a circle along with them). Even then, it is a made up explanation for what appears to be happening. What we call "centrifugal force " is just inertia. It is the tendency of an object to keep going in a straight line at constant speed. If the camera is whipping around in a circle, it isn't staying on a straight line, so an object going straight sees the camera moving funny and the camera sees the object "moving funny " but it's the camera that is accelerating, not the object, even though it looks as if the object is from the camera's point of view. In a way, Newton's first law says, "Inertial frames exist. " In other words, it is a fact of the Universe that you can find ways to move so that lots of objects are clearly obeying the law of inertia, and any deviations from that are explainable with read forces such as gravity. Inertial frames are the frames where the motions of the most objects look the simplest. I guess another simpler way to answer your question is this: suppose two astronauts are floating together with nothing nearby. They push off. A says B is moving in the positive X direction, and B says he isn't, that A is moving in the negative X direction. They see "equal and opposite velocities " but they don't "cancel out. " They really are moving apart. For purposes of doing physics 1 problems, stick to inertial frames; don't have your axes ride around and around a given axis, for example. Don't accelerate. Then, when you are drawing forces, never draw centrifugal forces, because they aren't really there. They are just an illusion anyway and you are not in a place where you can even see the illusion. Likewise, if you think something is going in a circle, do NOT write a force and label it "centripetal " force. "Centripetal " is a description of direction, not a stuff. "Centripetal " does not mean gravity or friction or tension, it means "inward. " You need to figure out WHY the object is going in a circle, and the reason is gravity or friction or tension or some real, actual force, which you can then say is the "centripetal " force if you really want to, but all you are doing is repeating that, "this is the force that happens to point inward. " I hope this helps.

Posted by: Everybody's Screaming on 2010-02-25, 12:48:36

There's actually no such thing as centrifugal force. Centrifugal force is simply inertia. Your body wants to stay in a straight line while turning so you experience this "force " that pushes you outward. But the real force is centripetal force that makes you turn. If there is this force that makes it cancel, you would be going in a straight line.