centrifugal force

[devrimci_kürt]

centrifugal force does not actually exist but we feel it....why?

[tvp45]

When you say you feel the centrifugal force, what exactly are you feeling? Suppose you are riding in a car that goes around a sharp turn. Are you feeling a tendency to slide across the seat, or are you feeling the seat belt holding you in place?

[swansont]

We assume the world to obey Newton's laws of motion, i.e. we assume we are in an inertial frame. When we aren't, we assume a force that isn't really there, in order to account for the motion.

[iNow]

Correct me if I'm wrong, but the effect itself does exist, it's just not able to be considered as a force for definitional reasons? IIRC, it's basically a pseudoforce, not a non-existant effect. We feel the effects, just cannot use the word "force" to describe it since that is not accurate.

[Kyrisch]

Correct me if I'm wrong, but the effect itself does exist, it's just not able to be considered as a force for definitional reasons? IIRC, it's basically a pseudoforce, not a non-existant effect. We feel the effects, just cannot use the word "force" to describe it since that is not accurate.

 

Yeah, the effect exists. It's like the Coriolis "Force" which causes the air to eddy because of the rotation of the earth. It's just not a force.

[NowThatWeKnow]

I understood that centrifugal force is an "apparent" force that is directed away from the center, but it is actually inertia telling a body in motion to stay in motion in a straight line.

[D H]

Correct me if I'm wrong, but the effect itself does exist, it's just not able to be considered as a force for definitional reasons? IIRC, it's basically a pseudoforce, not a non-existant effect. We feel the effects, just cannot use the word "force" to describe it since that is not accurate.

We do not and cannot feel the effects. That is one of the distinguishing features that differentiates pseudo forces from "real" forces. There is no way to measure pseudo forces (e.g., inertial force, centrifugal force, Coriolis force, gravity). You can observe the effects of these pseudo forces in terms of observed acceleration. That leads to the other distinguishing features that differentiate pseudo forces from "real" forces: (1) The magnitude of a pseudo force is proportional to the mass of the object subject to the force, and (2) Pseudo forces vanish in some reference frames (inertial frames).

[boywonder]

centrifugul force is created by momentum therefore you are being imposed upon by the actual force momentum. objects in motion tend to stay in motion when an object vectors or changes trajectory it resist as a result of newtons laws. the law of inertia works because the electrons in the givin matter are spinning in a single direction they too donot want to change direction making true the law of inertia.

[D H]

boywonder, please stop spouting nonsense.

[boywonder]

boywonder, please stop spouting nonsense.

 

mtheory

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Merged post follows:

Consecutive posts merged

boywonder, please stop spouting nonsense.

oh my god !the last person you know that would be a physics expert would be a person who would advertise it .SAD Edited February 3, 2009 by boywonder
Consecutive posts merged.

[mooeypoo]

boywonder, we do not accept ad-hominem attacks in this forum.

 

Please read our rules and follow them. You are expected to participate in a debate and not hijack it for your own personal thoughts; and you are expected to do so following the scientific method, which means you should argue factual data or, at the very least, explain your controversial conclusions, while making claims.

 

Please read the rules.

[D H]

M theory does not say anything close to what you said in post #8. You are too young to even begin to grasp the math.

 

In particular,

centrifugul force is created by momentum therefore you are being imposed upon by the actual force momentum.

Wrong. Centrifugal force exists only in the eye of a non-inertial observer. Observe the behavior of some object from the correct frame of reference (an inertial frame) and there is no centrifugal force.

 

 

objects in motion tend to stay in motion

Correct. Newton's first law.

 

 

when an object vectors or changes trajectory it resist as a result of newtons laws.

This doesn't make much sense as written. I know what you are trying to say, but Newton said it much better.

 

 

the law of inertia works because the electrons in the givin matter are spinning in a single direction they too donot want to change direction making true the law of inertia.

Wrong, for many reasons. (1) Spin has nothing to do with mass or momentum. While spin does lead to some macro-world manifestations such as magnetism, Newton's laws of motion are not a result of spin. (2) Electrons have very little to do with mass and momentum. Think about it this way: a proton's mass is about 1836 times that of an electron. (3) Two wrongs do not make a right, at least in this case. The spin of an electron has absolutely nothing to do with inertia.

[Gareth56]

We do not and cannot feel the effects. That is one of the distinguishing features that differentiates pseudo forces from "real" forces. There is no way to measure pseudo forces (e.g., inertial force, centrifugal force, Coriolis force, gravity). You can observe the effects of these pseudo forces in terms of observed acceleration. That leads to the other distinguishing features that differentiate pseudo forces from "real" forces: (1) The magnitude of a pseudo force is proportional to the mass of the object subject to the force, and (2) Pseudo forces vanish in some reference frames (inertial frames).

 

I thought the gravitational force was a "real" force? Or is gravity not the same as Fgrav ?

 

Thanks

[swansont]

I thought the gravitational force was a "real" force? Or is gravity not the same as Fgrav ?

 

Thanks

 

Not when you get to the point that you study General Relativity. Sitting still in a gravity field is not an inertial frame — freefall is.

[Gareth56]

Sorry swansont you've lost me again

[Sisyphus]

I think the idea is that falling freely in a uniform gravitational field is indistinguishable from just sitting there in space, not moving or moving uniformly (which are themselves the same thing), called an "inertial frame." Hence astronauts in freefall orbits seeming "weightless," even though the Earth's gravity is almost as strong there as it is on the surface. So if accelerating in a gravitational field is equivalent to an inertial frame, then resisting the field (that is, "not moving," e.g. standing on the Earth's surface) is equivalent to accelerating, making it non-inertial.

 

Er, right, D H?

[Gareth56]

Thank you. So a "real force" is a force that you can measure if you're in freefall or moving uniformly?

 

What are examples of "real forces"?

[D H]

I think the idea is that falling freely in a uniform gravitational field is indistinguishable from just sitting there in space, not moving or moving uniformly (which are themselves the same thing), called an "inertial frame."

That's correct. The idea "that falling freely in a uniform gravitational field is indistinguishable from just sitting there in space" is Einstein's equivalence principle. This is one of the key concepts that underlies General Relativity. The equivalence principle is presently the most precisely verified concept in all of physics.

 

One way to think about it: The Newtonian and GR concepts of an "inertial frame" should certainly coincide in a region of space far removed from any massive body. A non-rotating, non-accelerating spacecraft placed in this region can serve as the basis for an inertial frame. Similarly, if the spacecraft now starts accelerating at 1g, the spacecraft can no longer serve as the basis for an inertial frame. The origin is accelerating. Accelerometers attached to the spacecraft will concur with this assessment. If the equivalence principle is correct, then a frame based on the spacecraft when the spacecraft is standing still on the surface of the Earth cannot serve as an inertial frame. The spacecraft's accelerometers will similar concur with this assessment by reporting that the spacecraft is accelerating *upward* at 9.8 m/sec². In general relativity, an inertial frame is a frame in which an accelerometer fixed with respect to the frame reports zero acceleration.

 

Thank you. So a "real force" is a force that you can measure if you're in freefall or moving uniformly?

Accelerometers measure the acceleration resulting from "real" forces. Spring scales similarly measure real forces. Your bathroom scale does not measure your weight (acceleration due to gravity times your mass). It measures your "apparent weight" -- the net force acting on your body less gravitational force, or in GR parlance, the net force acting on your body (period).

 

What are examples of "real forces"?

There are four fundamental interactions in physics: gravity, the weak force, electromagnetism, and the strong force. The weak and strong forces don't (as far as I know) manifest themselves in macro-world phenomena that you can feel. (You would not feel an atomic bomb going off next to you. You would die instantly.) Since gravitation cannot be measured (see caveat below), that leaves the electromagnetic force. The feeling from the chair/floor you are sitting/standing on, the wind blowing on your face, your feet scuffing on the floor: These are all macro-world manifestations of electromagnetism.

 

Caveat: The equivalence principle talks about the indistinguishability between a uniform gravitational field and acceleration. There is no such thing as a uniform gravitational field. Stars and planets, for example, have nearly spherical gravitational fields. Extend your arms horizontally. Gravity is pulling your left hand in a slightly different direction that your right hand. If you had an extremely sensitive six foot strain gauge, you could measure the gravity gradient (aka tidal gravity) across the span of your hands. Tidal gravity is a "real" force.

 

 

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One last item, a challenge. An inertial navigation system uses accelerometers and gyroscopes to measure the accelerations and angular velocity of an airplane or spacecraft. The INS' computer integrates these accelerations and rotations over time to yield the vehicle's position and orientation. The challenge: Explain how an INS can possibly function properly given that accelerometers cannot measure the acceleration due to gravity.

[Gareth56]

Thanks DH, I'm clinging on by my fingernails but it's interesting stuff. One thing I came across over here was a gravity wave detector being built. Are these waves that are caused by the force of gravity?

 

Gravity Waves