# 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.

• 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. Commented Feb 26, 2014 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. Commented Feb 26, 2014 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. Commented Feb 26, 2014 at 16:05
• Related: physics.stackexchange.com/q/8891/2451 and links therein. Commented Feb 26, 2014 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. Commented Feb 27, 2014 at 4:39

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:

(source: ydcdn.net)

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.

• And to add to a good answer: centrifugal 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). Commented Feb 27, 2014 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. Commented Feb 27, 2014 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.

• 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. Commented Feb 26, 2014 at 22:33

Anupam has very well answered, I'll just add my modest contribution with a simple example: the inertial frame could be the Earth and the non-inertial frame a car moving in a circle. In that case the centripetal force is the reaction of the tyres on the ground due to their grip, but the most interesting thing about this case is that objects in the car seem to be pushed outward. In reality (meaning, in an inertial frame, which the Earth can be considered for a short duration) they simply tend to continue in a straight line: this force, the centrifugal force, is only fictitious and is due to the fact that the lines that solids tend to go along in inertial frames might not be lines in a non-inertial frame (viewpoint problem). The car itself experiences the centrifugal force because after all it is yet just another thing bound in a non rigid way (i.e. suspensions) to the tyres which propagate the centripetal force. This is why they can topple at great speeds (higher centrifugal force).

Centripetal forces are not forces which are developed on their own; actually, it is produced under the action of different forces FOR EXAMPLE: If a man moves on a road in circular path. Centripetal force is provided by FRICTIONAL FORCE Similarly when earth moves around sun the centripetal force is provided by the gravitational force. So, the centripetal force is not a force itself; it can be produced under the action of several forces.