# What is the reaction force of centripetal force

• Zynoakib
In summary, Newton's 3rd law states that in an inertial frame of reference, the tension in a string creates a reaction force. Centrifugal force is considered as a pseudo-force because it is not a new kind of force, it only refers to the force which is responsible for circular motion of an object- in this case, the tension.
Zynoakib
According to Newton's 3rd law, force exists in pair. When I attach a ball to a rope and rotate it, I am giving the ball an centripetal force to keep it moving in circular motion, so is the tension in the string the reaction force I am asking?

I also want to ask about the reason why centrifugal force is considered as a pseudo-force. My explanation is that when you stand on the ball (imagine), you experience both the centripetal force (because you are rotating with the ball) and the centrifugal force (because you feel a force pushing you outward), but noting is actually providing the centrifugal force, and this also makes the rotating frame of reference an non-inertial frame. Is it correct?

Thanks!

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Centripetal force is not a new kind of force . It only refers to that force which is reponsible for circular motion of an object - In this case , the tension .

*In inertial frame -
Tension is not equal to some other force mw2r . Acceleration is caused due to tension and this tension is simply equal to m*a , and a = w2r .

*In non inertial frame of the ball , you now add a pseudo force , simply following Newton's law for the non-inertial frame .
You call this force the centrifugal force .

Zynoakib said:
My explanation is that when you stand on the ball (imagine), you experience both the centripetal force (because you are rotating with the ball) and the centrifugal force (because you feel a force pushing you outward), but the centrifugal force should theoretically cancel the centripetal force, making the circular motion impossible and violating the law of motion (because you are still rotating with the ball), which also makes the rotating frame of reference an non-inertial frame. Is it correct?

It doesn't make the circular motion impossible . Would you consider your accelerating car ( from inertial frame ) to be moving while sitting in it ( a non inertial frame ) ?
Now , coming to your question , if you sat on the ball , would you see the ball accelerating ? As you said , Fnet = 0 and I just said , a =0 .

So is Newton's law being invalidated ?

*Just so you know , there's a like button near the bottom which you can press if somebody's post helps .

Zynoakib
Just to check my concept, in inertial frame where F = ma is obeyed, there is no reaction force for centripetal force because the force is just tension, while in non-inertial frame, centrifugal force is added to "balance" the centripetal force as stated by the Newton 3rd law; otherwise, the law will be invalidated.

Hope its correct this time

Thanks anyway

Zynoakib said:
you experience both the centripetal force (because you are rotating with the ball)
You may not experience. You just feel like something pull you out, which you stated it after this, a pseudo force. This experience is one of the key for Einstein to establish General Relativity.

Zynoakib
Zynoakib said:
there is no reaction force for centripetal force because the force is just tension
Of course not, for tension is made by the molecules on the rope! It's a real force so it must have a reaction, which is the force from the rope.

Zynoakib
tommyxu3 said:
Of course not, for tension is made by the molecules on the rope! It's a real force so it must have a reaction, which is the force from the rope.
so does that mean the reaction force for centripetal force is the force from the rope, and tension is kind of like a "medium" to provide centripetal force?

tommyxu3 said:
Of course not, for tension is made by the molecules on the rope! It's a real force so it must have a reaction, which is the force from the rope.

The tension is the centripetal force .

Qwertywerty said:
The tension is the centripetal force .
Yes, it is.
Zynoakib said:
so does that mean the reaction force for centripetal force is the force from the rope, and tension is kind of like a "medium" to provide centripetal force?
Yes. The rope makes the force, a centripetal force that the rope pulls you, so the reaction must be a force you pull the rope.

Zynoakib and Qwertywerty
Zynoakib said:
I am giving the ball an centripetal force to keep it moving in circular motion, so is the tension in the string the reaction force I am asking?
https://en.wikipedia.org/wiki/Reactive_centrifugal_force

Zynoakib said:
I also want to ask about the reason why centrifugal force is considered as a pseudo-force. ...
https://en.wikipedia.org/wiki/Centrifugal_force

Note that these two are different things (see table in the first link). The modern use of "centrifugal force" usually means the later (inertial force existing in rotating frames only).

Zynoakib
tommyxu3 said:
Yes. The rope makes the force, a centripetal force that the rope pulls you, so the reaction must be a force you pull the rope.

Yeah - that's correct .

Thank you all guys I think I have had a better grasp of the concept!

## 1. What is the difference between centripetal force and reaction force?

Centripetal force is the force that keeps an object moving in a circular path, while reaction force is the equal and opposite force exerted on the object by the center of rotation. Centripetal force is the cause, while reaction force is the effect.

## 2. Is reaction force always equal to centripetal force?

Yes, according to Newton's third law of motion, for every action (centripetal force), there is an equal and opposite reaction force. This means that the magnitude of reaction force is always equal to the magnitude of centripetal force.

## 3. Can an object experience centripetal force without a reaction force?

No, an object cannot experience centripetal force without a reaction force. As mentioned before, centripetal force and reaction force are two sides of the same force, and one cannot exist without the other.

## 4. How does the direction of reaction force relate to the direction of centripetal force?

The direction of reaction force is always opposite to the direction of centripetal force. This means that if the centripetal force is pulling an object towards the center of rotation, the reaction force will be pushing the object away from the center in the opposite direction.

## 5. What is the role of reaction force in circular motion?

Reaction force plays a crucial role in circular motion as it allows an object to maintain its circular path. Without a reaction force, an object would continue in a straight line instead of a curved path. It is the reaction force that balances out the centripetal force and keeps the object in equilibrium, allowing it to move in a circular motion.

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