Why do we teach that centripetal force is the main force, while the centrifugal force is the reaction force?
Isn't it much more intuitive to think of it the other way?
Centrifugal tries to break the mass off the string, similar to how an applied manual force tries to pull things.
Centripetal is a reaction to the centrifugal, similar to how a structure opposes human-input force.
obviously the "human input" in circular motion is the circular motion itself, and petal and fugal both arise from that. But the fugal force acts in the direction that breaks the string, so it's more similar to an applied manual force.
Moreover, the apparent centrifugal force (imagine a can on a rotating string with a marble inside it, the marble stays on the end of the can not tied to the string) acts by itself, without a centripetal force.
Isaiah Gray
centripetal force is the force in an inertial coordinate system that causes an object to turn (ie the component of force orthogonal to motion).
centrifugal force is a fictitious force introduced by doing your physics in an non-inertial (read accelerating) reference frame. it is not a "reaction force", or whatever.
centripetal is the easier to understand of the two.
Aaron Sanders
>centrifugal force is a fictitious force introduced by doing your physics in an non-inertial (read accelerating) reference frame. it is not a "reaction force", or whatever.
Why not? Centripetal points inward, and is a real force. There's a reaction for every force. So the fugal force is real.
I don't see how reference frame matters. Petal will always point inward. Fugal will always point outward. This is true even if I'm watching from an inertial reference frame.
Fugal is easier to understand, because physically unbound objects experience the fugal force.
Lucas Foster
The train wants to go in a straight line. The steel loop exerts an inward force that changes the straight line. Same thing with an elevator. When you're going up, you know there is no downward force--it's actually the force that is pulling the elevator upward.
Justin Cooper
>Why not? Centripetal points inward, and is a real force. There's a reaction for every force. So the fugal force is real. that's a non-sequitur. centrifugal force is NOT equal and opposite to centripetal force. centrifugal force is NOT a reaction force to centripetal force.
You can have a centrifugal force without having a centripetal force, because the former is an ARTIFACT of an accelerating coordinate system, whereas the latter is a force that can be attributed to a physical cause.
For instance, take a particle with zero net force traveling at constant velocity in an inertial coordinate system. if you now try to describe the motion of the same particle in a rotating coordinate system, you discover the force is non-zero with centripetal and Coriolis components. These forces are not caused by any physical process, they are "correction" forces to account for apparent accelerations (read changes in velocity) introduced by your spinning ass; particles with zero physical forces on them DO NOT travel in straight lines in non-inertial coordinate systems.
If you are having trouble distinguishing between real and fictitious forces, forget rotation for the moment and first try to understand linear motion in a non-inertial reference frame.
Leo Murphy
what you call them is irrelevant and for brainlets. Set up the equations consistently and your solution will be correct.
Jayden Brooks
Okay, I see what you're saying. The constraint of circular motion necessitates that there's always force acting on the mass, pulling it "inward circle loop".
If you look at a very small displacement within the circle, the acceleration vector is normal. So the centrifugal force is a reaction.
Thanks.
Sebastian Smith
because gravity pulls us down, and we feel that in our feet. in a roller coaster we feel like we're pulled towards our feet that's the connection they make
Carter Moore
I will say that there is still a problem with high school teachers referring to the fugal force as "fake". They should analogize it to the elevator, as a reaction force.
A reaction force that is dependent on the other forces. So yes, not equal, but almost always opposite, I get it now. It just fills in the gap to maintain the circular motion.
Robert Green
>So yes, not equal, but almost always opposite I don't know how you can say this if you admit you can have zero centripetal force and non-zero centrifugal force. I can make centrifugal and centripetal forces orthogonal to each other if you want an example. Trying to make a connection between these forces in your head is just plain wrong, because no connection exists.
>they should analogize it to the elevator, as a reaction force. but it isn't, and any analogy like that would lead to misunderstanding and confusion.
Jonathan Wood
I was talking about Person in elevator feels down force when going up. It's a reaction to the up force on the person (by the elevator).
Person in rollercoaster feels force because the rollercoaster accelerates if it travels in a circle, even at constant speed. The acceleration vector is orthogonal to velocity (you can work this out just by drawing it), so there is a reaction force away from the radius.
> if you admit you can have zero centripetal force and non-zero centrifugal force.
You can't. I thought so in the beginning of this thread, now it's become obvious I was wrong.
If you assume circular motion with constant speed, the rest of it just fills in. the "mass on a string" undergoes centripetal force, which is constant magnitude. The centrifugal force is just the reaction force of the mass accelerating "along" the circle.
>but it isn't, and any analogy like that would lead to misunderstanding and confusion.
It is exactly like the elevator reaction force, except it happens continuously at every point along the circle.
Jeremiah Cruz
>You can't i'm not going to do the full derivation here, but take a look at this section of the wiki article on rotating reference frames
Here the equation relates acceleration [math]\vec{a}_i[/math] in an inertial reference frame to the acceleration [math]\vec{a}_r[/math] in a reference frame rotating with constant angular velocity vector [math]\vec{\Omega}[/math]
here the [math]\vec{\Omega} \times(\vec{\Omega}\times\vec{r})[/math] term is the fictitious centrifugal acceleration, and the [math]- 2 \vec{\Omega}\times\vec{v}_r[/math] is the coriolis acceleration. The last term [math] - \frac{d\vec{\Omega}}{dt}\times\vec{r}[/math] is called the Euler acceleration, but is zero since we assumed [math]\vec{\Omega}[\math] is constant.
Clearly we can set [math]\vec{a}_i = \vec{0}[\math] for a body with zero net force in an inertial reference frame. Notice how neither of the centrifugal nor coriolis accelerations/forces are forced to zero? That means you can have a fictitious centrifugal force without physical centripetal force.
I will repeat, any connection you form in your head relating centripetal and centrifugal forces is JUST PLAIN WRONG. They are two completely different terms in the force law for a rotating coordinate system.
Liam Myers
fuck, i should check my latex next time before posting.
To drive this point home, if you have a body with a position on the axis of the rotating coordinate system, the centrifugal force is zero. However, you the body could be in the process of turning away from the axis, and as such would have a centripetal force.
In other words, I can come up with situations where you have zero centripetal force and non-zero centrifugal force, and situations where you have non-zero centripetal force and zero centrifugal force. I can also come up with situations where both are zero or non-zero.
Henry Allen
Okay. Where can I find out more about this sort of notation?
Is there a name for it?
David Cruz
the name of the notation is, uh, vector notation?
if you are interested in the non-inertial reference frames of classical mechanics, just pick up a classical mechanics book.
Landon Butler
centrifugal force is a fictitious force to ensure you are stationary in the rotating non intertial reference frame assuming pure rotation. Other stuff like Coriolis etc act when in non inertial frames.
It is analogous to the jerk during car acceleration in the opposite direction to the motion of the car.
in the frame of the accelerating car for example, the acceleration is zero. This should imply that the force in the accelerating reference frame also be zero. Hence a fictitious force is added to correct for the discrepancy of the inertia felt in an inertial reference frame.
These are not Newtons 3rd law pairs because they act on the same object and not on different objects.
This stuff is hard OP and I hope I bought some sense into you. Also this is my interpretation and correct me if i'm wrong.
Elijah Robinson
centrifugal force is a fictitious force to ensure you are stationary in the rotating non intertial reference frame assuming pure rotation. Other stuff like Coriolis etc act when in non inertial frames.
It is analogous to the jerk during car acceleration in the opposite direction to the motion of the car.
in the frame of the accelerating car for example, the acceleration is zero. This should imply that the force in the accelerating reference frame also be zero. Hence a fictitious force is added to correct for the discrepancy of the inertia felt in an inertial reference frame.
These are not Newtons 3rd law pairs because they act on the same object and not on different objects.
This stuff is hard OP and I hope I bought some sense into you. Also this is my interpretation and correct me if i'm wrong.
Dominic Peterson
Centrifugal force isn't real its just your perception of centripetal acceleration.
Nathaniel Moore
>centrifugal force Not a thing. F=ma; the mass (roller coaster) is accelerating (change in direction of velocity) towards the center of the loop, not away from it.
Ethan Butler
I thought centrifugal force was just the force experienced by the object exerting the centripetal force. For instance the force on the actual loop of the coaster
Noah Hughes
I want physics shits to go
Kayden Baker
A few things I don't get:
>Hence a fictitious force is added to correct for the discrepancy of the inertia felt in an inertial reference frame.
>These are not Newtons 3rd law pairs because they act on the same object and not on different objects.
Could you explain these two statements, and what they physically mean, intuitively?
Sebastian Mitchell
>centripetal force is the main force ...making an object move in an arc. >centrifugal force is the reaction force ...keeping the object from moving on a tangent. This is not rocket science, user.
Evan Mitchell
The centripetal force on the marble is applied by the bottom of the can, which it cannot pass through.
Joshua Cooper
A reference frame that is accelerating can be likened to the inside of a car speeding up. When the car accelerates, objects within it will remain at their current velocity (Newton's first law). If you look at this from the car's perspective, it will observe that the object are being 'pulled' backwards, when in reality it is the car (and reference frame) accelerating in the opposite direction. The same applies for when the car is turning, except the direction of the car's acceleration is always perpendicular to the direction of travel. The car is accelerating towards the inside of the circle that is created, and so the car will observe the occupants being 'pulled' towards the outside (when it is simply the objects tending towards a 'true' straight path).
Kevin Ward
> centrifugal force
Luke Thomas
Look at the image in this wiki. You are stationary wrt to the non inertial reference frame i.e the accelerating car. For you to accelerate as seen by a person in a inertial reference frame, you have a net inertial force of (m_human)*(acceleration of car) acting upon you.
But as I said previously you are still stationary wrt to the car and according to Newtons first law, you can only remain stationary if no forces act on you. Hence you have the same inertial force acting in the opposite direction to counteract the fact that you are in an accelerating reference frame.
It is not a Newton 3rd law pair as OP or someone else suggested because Newtons 3rd law acts on 2 separate bodies. For example if the centripetal effects cause you to accelerate to the center hence rotate and if you simultaneously feeling the centrifugal effects, you have an action and sort of 'reaction' acting on the same body
Angel Reed
different guy, can you explain in the diagram, what the force is that keeps the guy against the can?
Jacob Green
>acts by itself, without a centripetal force. fucking whoa there boyo back to school you go.
Brandon Reed
It's momentum. The man will try to continue in a straight line while the can tries to go in a circle, resulting in the man colliding with the can and changing his angle slightly, which repeats over and over.
Jace Howard
The centripetal force is not one force among others applied on the can, but the net force.
Lincoln Rodriguez
Uh, just because a centripetal force exists doesn't mean that a centrifugal force exists. It depends on the frame of reference.
In the frame where you see a ball on a string spinning in a circle, only a centripetal force exists. That is, the ball is being pulled towards the center of the circle by the string. Cut the string and that force, the only force, disappears.
In the frame of reference of the ball, there are two forces that cancel out. You have a centrifugal force pulling the ball away from the center of the circle and you have the pull of the string, the centripetal force. Cut the string and the centrifugal force will pull the ball away from the center.
The centrifugal force is a fictitious force. It only arises in a certain frame of reference.
Justin Cruz
the reaction of the surface of the can on the person
Brody Gomez
oops i meant the normal force as opposed to the reaction which i normally use interchangeably
you wrong son.. If the string is cut the ball moves in a line tangent to the circle of rotation. It's not 'pulled' by a non existing centrifugal FoRcE
Julian Morgan
>you wrong son Again, it depends on the frame of reference. In the frame of reference where the string is "at rest", a centrifugal force exists (as well as a Coriolis force).
The ball only moves in a straight line when you are observing the string spinning and the string is cut.
What appears to be a force in one frame of reference is just the natural (constant velocity , straight line) movement of mass in another frame. These are called fictitious forces since they can appear and disappear from one frame to another.
Samuel Martinez
If centrifugue doesn't get to be a real force, neither does gravity
Eli Peterson
user i'm not him but thank you for making Veeky Forums worth browsing today.
