I am having trouble understanding how centripetal force works intuitively.

This is my claim.

When I have a mass strapped on a string and spin it around, I feel the mass pulling my hand. So, I want to say that the mass is trying to move away from the center of the circle, and yet centripetal force makes it move in a circle, i.e, centripetal acceleration towards the center.

Similarly, when I am driving a car and making a curve, I feel being pushed away from the center of the curvature rather than towards it.

I am having so much trouble with these types of problems because of this counter intuitive concept. Can someone help me out?

  • $\begingroup$ I feel being pushed away from the center while centripetal force supposedly pushes me towards the center. $\endgroup$ – hyg17 Nov 12 '13 at 22:41
  • $\begingroup$ Related: physics.stackexchange.com/q/8891/2451 and links therein. $\endgroup$ – Qmechanic Dec 8 '13 at 21:23

The centripetal force is the one which mantains an object in a circular motion (changing the direction of velocity).

when I am driving a car and making a curve, I feel being pushed away from the center of the curvature rather than towards it.

In this case you are feeling inertia, your body tries to continue in straight motion. However, from you accellerated frame you can describe inertia as a centrifugal force.

So the problem is that you are confusing centripetal and centrifugal force. The former pushes you to the center, while the latter is a virtual force which pushes you to the outside.

  • $\begingroup$ I looked it up and it made total sense. It's basically the reaction force against the centripetal force, right? And it's called centrifugal force? $\endgroup$ – hyg17 Nov 12 '13 at 22:49
  • $\begingroup$ @hyg17 Not reaction force. Don't mistake centrifugal force for an action-reaction pair as per Newton's third law. That's not what's going on here. The centrifugal force is present in an accelerated reference frame (i.e. not inertial, aka not encountered in intro-to-physics courses). In the inertial frame, there is a single force, tension, which pulls the mass around in a circle; because of this it is called the centripetal force. In the car, the force you feel is friction. Inside a car on an incline OR a turning airplane, that force is the normal force. $\endgroup$ – Greg Nov 13 '13 at 6:14
  • $\begingroup$ I am so confused. Isn't a normal force a result of action-reaction pair ? As in, when an object is on a table, gravity pulls the object downwards but the table pushes it back ? So, if the car is moving in circles, the friction between the road and the tire causes the centripetal acceleration right ? During this process shouldn't I be feeling like I am being pulled towards the center of curvature instead of being pushed away from it ? $\endgroup$ – hyg17 Nov 14 '13 at 22:25

Here's another way to approach the issue you're having. Forget about circular motion and consider linear acceleration. When you're sitting in a car on a straight road, and then it speeds up, you accelerate forward. That is, there's a net force on you in the forward direction. However, in the car you feel like you're being push back into your seat; if the seat weren't there, your motion relative to the car would be backward.

This is exactly what's going on in the circular case while moving at constant speed; there's a net force on you toward the center of the circle, but it feels you're being pushed away from the center of the circle. Only we give them fancy names like centripetal and centrifugal.

For more info, look up terms like virtual force, pseudo force, or non-inertial frame.


protected by Qmechanic Jul 3 '14 at 23:56

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