# How centripetal force is created?

1. Apr 13, 2015

### LogU16

Hello, teachers.

Do we apply centripetal force ourselves Or is it created by some other source? What is the source? How is it created?

Many many thanks.

2. Apr 13, 2015

### Delta²

We can apply centripetal force to another object (but not to ourself) and set the object to a circular orbit.

If ourself is in circular orbit, then something else is apllying centripetal force on us.

The source of centripetal force can be anything, for example when we sit inside a car that does circles, then the centripetal force is applied on us by the seat of the car, or by the car's sidewall. The centripetal force to the car (because the car is also in circular orbit) is applied to the car from the friction between the car's tyres and the ground.

Last edited: Apr 13, 2015
3. Apr 13, 2015

### robphy

The centripetal force is a name for the "component of the net-force on an object that makes it go around a circle [that is, turns the velocity vector]".
It's not a new force... it need not have a single source...
It does not appear as "an additional force" on a Free-Body Diagram.
It is part of the net-force on the object.

4. Apr 13, 2015

### Dingu Sagar

Are Centripetal and centrifugal force come from the same origin ...or are they action and reaction forces ?

5. Apr 13, 2015

### robphy

They are related but in a complicated way...Centrifugal forces are fictitious forces in a non-inertial frame of reference

6. Apr 13, 2015

### Staff: Mentor

I really don't understand what you mean by the questions. "Ourselves"? "Other source?" "How?" Maybe on a more basic level you need to understand what centripetal force is, because those follow directly from any description. The answers might just be a pice of string (on a yoyo), gravity (for the moon) or a tire (for a car).

7. Apr 14, 2015

### rcgldr

Random examples of "ourselves" generating the tension that results in centripetal forse: a twirling pole dancer; the outermost ice skaters when a line of them are rotating in a circle; a water skier when traveling in a circular arc (the tension component in the tow line and the skier's arms), a gymnast doing rotations on a high bar, a gymnast swinging on "flying rings", a gymnast doing flips in mid air, ... .

Short video of the last two examples:

8. Apr 14, 2015

### LogU16

@russ_watters Sir, I mean to say; Do we apply centripetal force by our hands Or is it generated by itself? What is the cause for this force?

9. Apr 14, 2015

### Staff: Mentor

We can apply it with our hands -- many examples were already given.

10. Apr 14, 2015

### LogU16

Thank you Sir, could you give me one or two examples in which we apply this force by our hands?

11. Apr 14, 2015

### Staff: Mentor

This is getting frustrating: did you not read the examples already given? Is there anything specific you don't understand about any of them?

12. Apr 14, 2015

### LogU16

@russ_watters Sir, I have read the examples but I am unable to differentiate where we apply this force by our hands.

The examples which I'm confused about are;
1) A small stone attached to a string moving in a circle
2) Rotation of earth around the sun
3) movement of a car in a circle on the road
4) A person running in a circle

Could you please tell me what's the source of generating the centripetal force in above four examples?
Many many thanks!

13. Apr 14, 2015

### rcgldr

1) A small stone attached to a string moving in a circle - the person's hand pulls inwards on the string, creating an inwards force, but most of the centripetal force is exerted by the string onto the stone.

2) Rotation of earth around the sun - hands are not involved.

3) movement of a car in a circle on the road - hands are not involved.

4) A person running in a circle - hands are not involved (feet are).

Read post #7 again for examples of centripetal force being applied via a persons hands.

14. Apr 14, 2015

### LogU16

Thanks, Sir @rcgldr. I request you to please tell me the cause of centripetal force in examples 2,3 and 4 too.

15. Apr 15, 2015

### Staff: Mentor

Can you apply what you have learned and attempt to answer that question yourself?

16. Apr 15, 2015

### LogU16

Ok Sir. I just try to answer, If you find any mistake in my explanation, please correct me here;

1) A small stone attached to a string moving in a circle >>> centripetal force is the tension force that string applies over the stone.
2) Rotation of earth around the sun >>> centripetal force is the force of gravity that is applied on the earth by the sun.
3) movement of a car in a circle on the road >>> centripetal force is the force of friction (present between tires and road) that is applied by the road on the car.
4) A person running in a circle >>> centripetal force is the force of friction (present between the feet and the ground) that is applied by the ground on the person.

Thanks a lot!