Relation between centrifugal force and speed

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Discussion Overview

The discussion revolves around the relationship between centrifugal force and speed, particularly in the context of driving on a circular highway on-ramp. Participants explore concepts related to centripetal and centrifugal forces, their effects on motion, and the implications for vehicle control while navigating curves.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants argue that centrifugal force does not increase overall speed but changes the direction of motion.
  • Others suggest that an increase in speed while turning could be due to factors like going downhill or accelerating, rather than centrifugal force.
  • There is a distinction made between centripetal and centrifugal forces, with some stating that centrifugal force is an apparent force in a rotating frame, while centripetal force is considered real and necessary for circular motion.
  • Some participants note that the centripetal force required for turning depends on the speed of the car and that friction plays a crucial role in maintaining control during turns.
  • Concerns are raised about the limitations of available friction, which can affect a vehicle's ability to navigate curves safely.
  • There is a discussion about the role of banked roads in providing centripetal force, with differing views on how gravity contributes to this force.
  • Some participants express confusion over the contributions of gravity and the geometry of banked curves, leading to further clarification attempts.
  • A few posts reflect frustration over the complexity of the discussion and the perceived need for clearer explanations, such as using free-body diagrams.

Areas of Agreement / Disagreement

Participants generally disagree on the role and implications of centrifugal force versus centripetal force, with multiple competing views on how these forces interact with speed and vehicle control. The discussion remains unresolved regarding the precise contributions of gravity and the effects of road banking.

Contextual Notes

Some participants express uncertainty about the definitions and distinctions between centrifugal and centripetal forces, as well as the conditions under which they operate. There are also unresolved mathematical considerations regarding the forces involved in circular motion.

physicsnewbie101
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Does centrifugal force generate in increase in overall speed? For example, if I am driving down a highway on-ramp which goes in a circular fashion, with my speed slowly increasing, does my overall speed increase because of the centrifugal force generated from the circular on-ramp? Is more force needed to control the car because of this?
 
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physicsnewbie101 said:
Does centrifugal force generate in increase in overall speed?
No. It changes the direction of the motion but not the speed.
physicsnewbie101 said:
For example, if I am driving down a highway on-ramp which goes in a circular fashion, with my speed slowly increasing, does my overall speed increase because of the centrifugal force generated from the circular on-ramp?
If your speed is slowly increasing it is because you are going downhill as you turn or because you are pushing on the accelerator or both.
physicsnewbie101 said:
Is more force needed to control the car because of this?
I don't understand the question. What is "this" that might require "more force" to control the car?
 
kuruman said:
No. It changes the direction of the motion but not the speed.
That's what the centipetal froce does in the inertial frame. The centrufugal froce is what balances the centipetal force in the rotating frame, where the car is static.
 
physicsnewbie101 said:
Does centrifugal force generate in increase in overall speed? For example, if I am driving down a highway on-ramp which goes in a circular fashion, with my speed slowly increasing, does my overall speed increase because of the centrifugal force generated from the circular on-ramp? Is more force needed to control the car because of this?

At some point, you need to learn about centripetal force, instead of "centrifugal force", which is only an "apparent force" when you are in a non-inertial reference frame. Centripetal force is "real", centrifugal force is nothing more than a reaction force to the centripetal force.

These are "central forces", meaning they act towards a center, and are always perpendicular to the direction of motion. If you've learned basic kinematics and basic vector addition, then a perpendicular force will not increase the speed or change the energy of motion. It merely changes the DIRECTION of motion. The force does no work.

Zz.
 
A.T. said:
That's what the centipetal froce does in the inertial frame. The centrufugal froce is what balances the centipetal force in the rotating frame, where the car is static.
That is true. It wasn't clear to me whether OP distinguishes the difference between centrifugal and centripetal force.
 
Centrifugal and centripetal forces typically act sideways on a car so can't increase its forward speed.

The centripetal force required to make the car follow a circular path depends on the speed of the car (actually speed squared) so the faster you go the more friction is required to make the turn. However the available friction is limited and can vary due to changes in the road surface. One moment there might be enough friction for a turn at the speed you are going and the next there isn't. This can affect the ability of the car to make smooth turns or even retain control. Friction is also needed to slow down or stop, and if it's all been "used up" providing centripetal force there will be none left for braking. In short it's never a good idea to drive so fast you run out of friction when you need it
 
CWatters said:
The centripetal force required to make the car follow a circular path depends on the speed of the car (actually speed squared) so the faster you go the more friction is required to make the turn. However the available friction is limited and can vary due to changes in the road surface.

With tight curves and/or high speeds, the road is banked so that the component of the force of gravity parallel to the road contributes to the centripetal force.
 
pixel said:
With tight curves and/or high speeds, the road is banked so that the component of the force of gravity parallel to the road contributes to the centripetal force.
Huh? You can break gravity into components perpendicular to the pavement and parallel the pavement, sure. But gravity is still a downward force whose projection in the centripetal direction is zero regardless. This means that if gravity has a component parallel to the pavement that in turn has a projection in the centripetal direction that is positive, then it also has a component perpendicular to the pavement that has a projection in the centripetal direction that is negative. Gravity cancels out as a contribution to centripetal acceleration.
 
The tilted pavement is a constraint that forces any motion in the direction of the centrifugal force to be associated with a gain in height. That gain in height is opposed by gravity.
 
  • #10
jbriggs444 said:
Huh?

As you so kindly point out, my statement was not correct. I was thinking that with a banked road the axis about which the car is rotating is tilted and the centripetal force pointed along the road. Not so. That's what happens when one discusses something one hasn't thought about in decades.

But I think it's correct to say that gravity does play a role, as without it there would be no normal force, the horizontal component of which is providing the centripetal force. Angle needed to keep the car on the road surface and moving in a circle: tanθ = v2/gr .

Would what I originally said apply if you were going around a banked curve and also going downhill?
 
Last edited:
  • #11
I have no idea why this is such a point of contention when one can easily and simply draw out the free-body diagram. In fact, that is what should have been done way in the beginning and would have saved a lot of discussion from the start.

This is basic physics. It should not be this painful to straighten out.

Zz.
 
  • #12
pixel said:
But I think it's correct to say that gravity does play a role, as without it there would be no normal force, the horizontal component of which is providing the centripetal force.
Also, the Big Bang plays a role, as without it there would be no ...
 
  • #13
A.T. said:
Also, the Big Bang plays a role, as without it there would be no ...

... sarcastic comments.
 

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