Centrifugal force, centripetal force, Coriolis effect, non-/inertial reference planes

[Stevisiov]

Okay, so I come across these now and again, and I have a few questions regarding them. I though I would keep them all to the same thread since they appear to be inter-related.

Firstly the obvious one. Is there such thing as centrifugal force? One of my engineering lectures said 'yes' when I asked him. My A-level physics teacher said there is no such thing as centrifugal force, he went on to say that it is sometimes useful to use it in calculations however.

Reading up on it describes it as a fictitious force that exists in a non-inertial reference plane. Unfortunately I don't know what a non-inertial reference plane is. So the second question; what is the difference between an inertial and non-inertial reference frame.

Okay, so I know what centripetal force is and that its responsible for overcoming inertia, allowing an object to travel in angular motion rather than the straight line the mass wants to follow. So, could centrifugal force really be described as a lack of centripetal force?

I also wanted to understand the Coriolis effect, and is this related to what we call these inertial and non-inertial reference planes? It seems to be a perspective trick, if you roll a ball across a rotating disc it appears to get deflected (I guess you might say it appears to be moved by a centrifugal force), but when viewed from above, the ball appears to move in a straight line, no apparent force is acting on it.

Here is a video of the example I was using.


Finally, is it ever suitable to use centrifugal force in certain calculations like my A-level physics teacher said? If so, when is and isn't centrifugal force suitable to use?

 

[ExigeEvan]

INB4FAMINE!

If you give something Kinetic Energy and no forces acting upon it then it's going to want to travel in a straight line.

By the merry go round spinning you round it's giving you KE. In effect you want to travel in a tangent off the merry go round. But, you'll hold onto something and this will cause a centripetal force that will act inwards.

The problem with centrifugal is people think if they let go of the merry go round they'll go out along the radius. They don't they follow the tangent from the point centripetal force released them.

This may be complete mumbo jumbo. If it is it'll give you an idea of how well my degree is going :/

 

[Exorcet]

Inertial reference frame = no acceleration

Non Inertial = acceleration

Any IRF is the same in terms of physics, so dropping a ball while standing still in a room is exactly like dropping a ball in a room that is moving at a constant 5,000,000,000 mph velocity (not just speed). Dropping a ball in a room that is accelerating at 5,000,000,000 mph/s however is different, it seems as if the ball accelerates to one side at 5,000,000,000 mph/s. This is because the room is accelerating, but the ball that has no contact with the room when free falling does not accelerate.

Centrifugal force isn't real, it results because of the inertia of a mass that is being rotated. For example, when spinning a ball and chain, the ball wants to fly off in a tangential direction, only the centripetal force of the chain keeps it from doing so. In the non inertial frame of the ball (ie, if you were standing on the ball exactly where the chain connected) you would feel a force pulling you on the surface of the ball, like gravity. That force doesn't really exist, it's just your inertia resisting circular motion.

The Coriolis effect is similar to the ball and chain thing. Something not firmly connected to the Earth will not rotate around the Earth's axis, so the free object will appear to change course on the non inertial frame of the Earth.

INB4FAMINE!
The problem with centrifugal is people think if they let go of the merry go round they'll go out along the radius. They don't they follow the tangent from the point centripetal force released them.

That's a good way to put it. The riders feel like there is a force parallel to the radius, but there is not.

 

[Bram Turismo]

Is there such thing as centrifugal force?

No, no such thing as that. An easy demonstration would be the Merry-Go-Round. If your seat would break off, you'd be sent in a straight line forwards, you wouldn't be suddenly flying off to the side. When in a circular motion, the velocity always is a tangent on the circle, as Evan pointed out. The force you are feeling is the seat pushing you inwards in order for you to keep the circular motion.

 

[daan]

Is this anything to do with the unintended acceleration of the Toyota Coriolis?

 

[Omnis]

No, no such thing as that. An easy demonstration would be the Merry-Go-Round. If your seat would break off, you'd be sent in a straight line forwards, you wouldn't be suddenly flying off to the side. When in a circular motion, the velocity always is a tangent on the circle, as Evan pointed out. The force you are feeling is the seat pushing you inwards in order for you to keep the circular motion.

Yeah, there is such thing as centrifugal force. Just like there is such a thing as Harry Potter, even though he doesn't exist.

Is this anything to do with the unintended acceleration of the Toyota Coriolis?

Here's another awesome video of the Coriolis effect as it works with the earth and winds.

 

[Stevisiov]

No, no such thing as that. An easy demonstration would be the Merry-Go-Round. If your seat would break off, you'd be sent in a straight line forwards, you wouldn't be suddenly flying off to the side. When in a circular motion, the velocity always is a tangent on the circle, as Evan pointed out. The force you are feeling is the seat pushing you inwards in order for you to keep the circular motion.

I understand the tangent at which objects fly off when centripetal force is removed and I know it is a property of inertia and not that of a real centrifugal force. What I wanted to know really, is that in a non-inertial reference frame, is it ok to talk about the fictitious centrifugal force? Since apparently it can be used in some calculations for the sake of simplification, I want to know when and where it is acceptable to use it. Apparently it is used in engineering although I don't know of any examples.

 

[Exorcet]

http://www.youtube.com/watch?v=o-BywEmKW8g

The passenger in the centrifuge is experiencing 6 g acceleration, so you could model the interior of the centrifuge as a stationary room with a sideways gravity force six times that of Earth's (and one vertical gravity force equal to Earth gravity).

 

[ExigeEvan]

http://www.youtube.com/watch?v=o-BywEmKW8g

The passenger in the centrifuge is experiencing 6 g acceleration, so you could model the interior of the centrifuge as a stationary room with a sideways gravity force six times that of Earth's (and one vertical gravity force equal to Earth gravity).

This.

You wouldn't use centrifugal force in a model of a rotating system, but of something within the system.

 

[Stevisiov]

Thanks, that's what I was getting at. 👍