# What is the cause of centripetal/centrifugal force?

What is the cause of centripetal/centrifugal force? When an object of mass $m$ is moved in a circular orbit, it experiences a centrifugal force radially away from the center. What is the cause of this centrifugal force? Is these related to the four fundamental forces (gravity,electromagnetic,weak and strong forces)?

This force is equivalent to a force experienced while stopping a mass in motion (Inertia). But is this inertia caused by some force? or what causes inertia? A photon particle does not have inertia of rest.

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It experiences no such force. Who told you that? As an aside, I suggest you read an introductory Physics text to learn the difference between an applied force (e.g. pushing something) and force due to a field. –  Carl Witthoft Feb 26 at 14:52
The force away from the center, which comes from the non-inertial coordinate system, is centrifugal force. The force toward the center, which keeps the object in orbit, is centripetal force. It can come from various sources: gravity, EM, tension in a string, etc. –  Ross Millikan Feb 26 at 15:21
Though this question is a bit naive, I don't see the point in the down vote. It is a fair question. Anupam hits the nail on the head, by the way. –  wgrenard Feb 26 at 16:05
Related: physics.stackexchange.com/q/8891/2451 and links therein. –  Qmechanic Feb 26 at 17:48
Deepak i noticed that your question is changed. Do you know about centrifugal force too in detail? To answer the first line of your question i have to explain the cause of centrifugal force. –  user31782 Feb 27 at 4:39
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Firstly you need to understand Newton's law's. basically the second law. Concisely second law is :"whenever we apply a force on an object this force changes object's velocity's magnitude if it is in the same direction as that of the direction of motion and changes the direction of motion if the applied force is not in the direction of motion."

When an object rotates uniformly in a circular orbit it doesn't experience any force(real or/and pseudo) radially outward. What it experience is the centripetal force which is always radially inward as measured from the co-ordinate system in which it rotates and is given by
$F={\dfrac{mv^2}{r}}$ where $m$ is the mass of that object, $v$ is the tangential instantaneous speed and $r$ is the radius of the circle in which it is rotating.
See this picture to visualize this:

To deviate the motion of an object from straight to circular we have to apply a force radially inward because due to inertia the object tends to move in a straight line. The force we apply changes velocity of that object by changing the direction of motion.

It should be noted if the force is calculated from some non-inertial frame of reference then we will have to add a pseudo force on that object but the motion will not remain circular in this non-inertial frame.

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And to add to a good answer: centri*fugal* force is an illusion - it is just a name people give to the unrestricted, inertia-guided movement when a centripetal force stops (e.g. when a string snaps). –  Amadan Feb 27 at 1:50
@Amadan CEntrifugal force is not an illusion. Nor it is inertia guided. It only comes into play when we switch our frame of reference to a revolving one. This appears to hold Newton's second law. I edit my answer soon. –  user31782 Feb 27 at 10:55

A centripetal force is not a fundamental force. We call any force a centripetal force if it is acting towards the center of the direction of rotation, perpendicular to the direction of motion.

Rotating a rock tied on a string? Centripetal force = tension in the string

Satellite orbiting Earth? Centripetal force = gravity

Charged object rotating around an opposite charge? Centripetal force = electromagnetic force.

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In an important sense, centripetal force is not a force at all. Consider an object executing simple circular motion. Add up all the forces on the object. The resultant (net) force point toward the center, and we call it centripetal. The centripetal force is the sum of the real forces, not an interaction between two objects, not a separate force itself. –  garyp Feb 26 at 22:33