Does the label "centripetal force" ever appear in a FBD

• Physics345
In summary, the homework statement does not mention the term "centripetal force." There are other factors that cause circular motion such as velocity.
Physics345

Homework Statement

Does the label "centripetal force" ever appear in an FBD? Explain.

None.

The Attempt at a Solution

No, centripetal force does not appear as a label on a FBD. Since it is not specific enough it does not tell us what the force is that’s keeping the object in motion, making it an unconventional label.

Physics newb here. I'm too green to be confident with wording problems!
Thanks for taking your time to help me out! Physics newb here.

Physics345 said:
Since it is not specific enough ...
You are on the right track. Can you be more specific about what you mean when you say "not specific enough"? What makes a force in a FBD "specific enough"?

kuruman said:
You are on the right track. Can you be more specific about what you mean when you say "not specific enough"? What makes a force in a FBD "specific enough"?
Hi Kuruman, thanks for the quick reply! Well considering there is other factors that cause centripetal force which represents circular motion but it isn't the cause of of that circular motion there are other factors that cause circular motion such as velocity. =)

Physics345 said:
Well considering there is other factors that cause centripetal force which represents circular motion but it isn't the cause of of that circular motion there are other factors that cause circular motion such as velocity. =)
Velocity does not cause circular motion. Imagine driving a car in a straight line on a horizontal surface. You push on the accelerator, yet you don't cause circular motion. How do you get the car to execute circular motion? Answer: You turn the steering wheel. Now imagine a FBD of this car going around in a circle at constant speed. What generates the forces that are in this FBD, how would you label these forces and why?

kuruman said:
Velocity does not cause circular motion. Imagine driving a car in a straight line on a horizontal surface. You push on the accelerator, yet you don't cause circular motion. How do you get the car to execute circular motion? Answer: You turn the steering wheel. Now imagine a FBD of this car going around in a circle at constant speed. What generates the forces that are in this FBD, how would you label these forces and why?
Ah, sorry I meant that the velocity keeps something in a circular motion if it's moving at a certain speed in a rotation and it would be knocked out of that circular motion if it's moving too fast or too slow. But to answer your question, it would be the applied force, hopefully my lack of knowledge on the subject won't hinder me this time.

Physics345 said:
Ah, sorry I meant that the velocity keeps something in a circular motion if it's moving at a certain speed in a rotation and it would be knocked out of that circular motion if it's moving too fast or too slow.
So if I swing a ball in a circle at the end of a string at just the "right" velocity and suddenly the string breaks, the ball's velocity will keep it going in a circle?
Physics345 said:
But to answer your question, it would be the applied force, hopefully my lack of knowledge on the subject won't hinder me this time.
So you would draw a single force in the FBD and label it "applied force"? What piece of the Universe exerts this "applied force"? What is this force's direction? Could there be more forces than just this one acting on the car? If so, what are they?

It's not a matter of "lack of knowledge on the subject", but a lack of understanding. I am trying to sharpen that understanding by showing you what questions you should be asking yourself.

Physics345
kuruman said:
So if I swing a ball in a circle at the end of a string at just the "right" velocity and suddenly the string breaks, the ball's velocity will keep it going in a circle?

So you would draw a single force in the FBD and label it "applied force"? What piece of the Universe exerts this "applied force"? What is this force's direction? Could there be more forces than just this one acting on the car? If so, what are they?

It's not a matter of "lack of knowledge on the subject", but a lack of understanding. I am trying to sharpen that understanding by showing you what questions you should be asking yourself.
To answer your first question, the ball would go in the direction it snapped at, let's say it snapped eastward it would continue at the same velocity of the rotation [eastward]
Ohhh I think I got it, the resisting forces such as the tension force or the friction force.

Also I appreciate you trying to help me understand, it means so much more when I figure it out, instead of being told.

Physics345 said:
Ohhh I think I got it, the resisting forces such as the tension force or the friction force.
Very good. It's the tension in the case of the string and the force of friction in the case of the car that cause the circular motion. Two more questions
(a) If you were to draw these forces in their respective FBDs, how would you label them? "Resisting" force is not a good name because they do not resist anything.
(b) How would you describe the direction of each of these forces?

FT in the case of a string spinning in the vertical plane
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Fg
Up positive so the tension force would be pulling on the string towards the the center of the rotation

Car

FN
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----------------------Ff
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Fg
right and up positive
and the car would be pulling towards the turn if i were to take a right turn, it would push me towards the other side of the turn towards the center of the circlenote I need to make a photo bucket account to make a diagram on word it would more accurately, describe my visualization.

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kuruman said:
Very good. It's the tension in the case of the string and the force of friction in the case of the car that cause the circular motion. Two more questions
(a) If you were to draw these forces in their respective FBDs, how would you label them? "Resisting" force is not a good name because they do not resist anything.
(b) How would you describe the direction of each of these forces?
Okay I am back! let me know what you think.
Edit: I made a few adjustment after I got some energy which allows me to get to work!

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Physics345 said:
Okay I am back! let me know what you think.
Very good. Note that the tension is centripetal in the first case and friction is centripetal in the second case. Why did you not label them "Centripetal force" in your diagrams?

Physics345
Because Centripetal force is just broadly defining other forces that cause centripetal motions, while Tension force and friction force are specific representations of the forces that are in motion causing centripetal force! wow thank you. I feel like I have a much better understanding of what's going on now. I can't believe I even mentioned velocity causes centripetal motion... Thank you for the enlightenment!

No, centripetal force does not appear as a label on a FBD. Since it is not specific enough it does not tell us what the force is that’s keeping the object in a centripetal motion, making it an unconventional label. Considering the previous statement a more specific label would be the actual force that’s pulling towards the center of the circle, causing the centripetal motion. For example tension force or friction force causing the centripetal force/motion.

This is my final statement, let me know what you think. Do I get your approval?

Physics345 said:
This is my final statement, let me know what you think. Do I get your approval?
Good enough. "Centripetal" denotes a direction. We don't label forces in FBDs as "centripetal" for the same reason that we don't label forces as "vertical" or "horizontal". As you say, not specific enough.

Physics345
Physics345 said:
No, centripetal force does not appear as a label on a FBD. Since it is not specific enough it does not tell us what the force is that’s keeping the object in a centripetal motion, making it an unconventional label. Considering the previous statement a more specific label would be the actual force that’s pulling towards the center of the circle, causing the centripetal motion. For example tension force or friction force causing the centripetal force/motion.

This is my final statement, let me know what you think. Do I get your approval?
In different words, it is merely the radial component of the resultant force, not an applied force.
In either wording, that's probably the answer they are looking for.

That said, I think it is acceptable to show a resultant force as long as it is clearly distinguished from applied forces. E.g. in "parallelogram of forces" diagrams it is common to show two applied forces with single arrowheads and the resultant with a double arrowhead. In the same way, you could show the resultant force resolved into tangential and radial components, each with a double arrowhead.

CWatters

1. Does every object undergoing circular motion have a centripetal force acting on it?

Yes, centripetal force is always present in objects undergoing circular motion. It is the force that keeps the object moving in a circular path and prevents it from flying off in a straight line.

2. How is centripetal force represented in a free body diagram (FBD)?

Centripetal force is represented as a vector pointing towards the center of the circular motion on a free body diagram. This vector can be labeled as "Fc" or "Fcent" to indicate the centripetal force.

3. Is centripetal force the only force acting on an object in circular motion?

No, an object in circular motion can have other forces acting on it, such as gravity, friction, or tension. However, the centripetal force is the only force responsible for the object's circular motion.

4. Can the direction of centripetal force change during circular motion?

Yes, the direction of centripetal force can change as the object moves along the circular path. This is because the direction of the force is always pointing towards the center of the circle, which changes as the object moves.

5. How does the magnitude of centripetal force change in different circular motions?

The magnitude of centripetal force depends on the mass, speed, and radius of the circular motion. A larger mass, higher speed, or smaller radius will result in a larger centripetal force needed to keep the object in circular motion.

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