At what point is research just plane stupid?

[scaryjim]

... That people get their knickers in a twist over centrifugal vs centripetal is a joke to me. ...

I find it amusing, and I kind of understand the confusion, as a passing analysis does strong imply that there should only be one force acting on the object in motion. Angular acceleration is a pain, frankly, and a full understand actually steps a little over my level of physics attainment.

OTOH the basic principle of opposition of forces doesn't suddenly get lost just because something's moving in a circle. It just makes the maths a lot more difficult...

[Ttaskmaster]

If centrifugal force don't exist, how come a centrifuge does, hmm.......?

[peterb]

If centrifugal force don't exist, how come a centrifuge does, hmm.......?

Because the centrifuge is being accelerated. The video disproving an outward force ignores the fact that there is no external force acting on the ball - it is just coasting. the energy to accelerate it is put in when the demonstrator swirls the ring. A ball on a piece of string that you swirl around your head is being kept in motion by the energy you impart - and the only way that can get to the ball is via the piece of string - and string is pretty bad at imparting force in compression.

Substitute string for cotton, and as you speed up the rotation by putting more energy in to overcome dynamic losses and the cotton will break.

[ik9000]

I find it amusing, and I kind of understand the confusion, as a passing analysis does strong imply that there should only be one force acting on the object in motion. Angular acceleration is a pain, frankly, and a full understand actually steps a little over my level of physics attainment.

OTOH the basic principle of opposition of forces doesn't suddenly get lost just because something's moving in a circle. It just makes the maths a lot more difficult...

Not that difficult. It's year 1 engineering stuff and easily within the grasp of anyone who did A-level maths/physics. Even gyroscopes and the like the maths isn't that much harder, once you've accepted the concepts behind them. It was fluid mechanics CFD, vector calculus, tensors, and the like, now that stuff is where it got difficult.

[Ttaskmaster]

The video disproving an outward force ignores the fact that there is no external force acting on the ball

Can't see vids at work, but I assume (this time without joking so much) it's something along the lines of how a sling works?

I was going to add another semi-serious question about curving a bullet using rotational force (which I believe is not possible without a planet-sized obstacle to curve it round), but gave up trying to figure out how to phrase it sensibly...

[Top_gun]

Not that difficult. It's year 1 engineering stuff and easily within the grasp of anyone who did A-level maths/physics.

Unlucky for ScaryJim, I done A'Levels in maths, physic and chemistry!

[Top_gun]

Here's a nice explanation on the BBC website:

http://www.bbc.co.uk/schools/gcsebit...on/revision/1/

[scaryjim]

Unlucky for ScaryJim, I done A'Levels in maths, physic and chemistry!

Lucky for me, I also did A-Levels in Physics and Chemistry. And did quite well in them.

I'm going to give you a single line from Wikiepdia's explanation of Newton's third law, that demonstrates why arguing for either centrifugal or centripetal force is demonstrably wrong:

... there is no such thing as a force that is not accompanied by an equal and opposite force. ...

You can't have a centripetal force without a centrifugal force. Or, you can't have Newton's third law. Which would you like to do away with?

[Top_gun]

Lucky for me, I also did A-Levels in Physics and Chemistry. And did quite well in them.

I'm going to give you a single line from Wikiepdia's explanation of Newton's third law, that demonstrates why arguing for either centrifugal or centripetal force is demonstrably wrong:



You can't have a centripetal force without a centrifugal force. Or, you can't have Newton's third law. Which would you like to do away with?

I fully accept Newton's Third Law. I think you still clutching of straws over centrifugal force though.

[scaryjim]

I fully accept Newton's Third Law. I think you still clutching of straws over centrifugal force though.

Wait, what?

You accept that every force has an equal and opposing force, yet you deny that centripetal force has an equal and opposing force?

[SeriousSam]

Centrifugal much like Coriolis and Euler is a fictional force which has to be "invented" in order to allow the use of newtons laws in a rotational frame of reference, as they were derived for an inertial frame of reference.

[scaryjim]

I think the key is that it only becomes relevant when two bodies interact, at which point it's ridiculous to say no such thing as centrifugal force as the interaction of the two bodies requires it. It may not play a role in the maintenance of the circular motion, but it is experienced by any object being affected by that circular motion.

[Ttaskmaster]

Surely the rotational force that gets and keep the thing moving is opposing gravity, though?
It wants to go round at 90º to gravity, while gravity wants to force it forward and down.... no?

In very basic terms, with a pencil sketch if I could...

[scaryjim]

Surely the rotational force that gets and keep the thing moving is opposing gravity, though?
It wants to go round at 90º to gravity, while gravity wants to force it forward and down.... no? ...

Sorry, I wasn't speaking in specifics.

If you want to plot the actual forces for keeping something in circular motion on Earth, then you can throw out all of the theoretical nonsense, because you need forces to overcome gravity, air resistance, the imperfect elasticity of whatever you're using to tether, friction between surfaces ...

Theoretically you can model a rotational system where a body that is already at motion is acted on by a force attracting it to the centre of rotation and it can be explained by the application of a single force. But that only works in the traditional "frictionless vacuum" that physicists are fond of because it makes the maths easier In a real rotational system on Earth there are far more forces to take account of...

[Top_gun]

Surely the rotational force that gets and keep the thing moving is opposing gravity, though?
It wants to go round at 90º to gravity, while gravity wants to force it forward and down.... no?

In very basic terms, with a pencil sketch if I could...

If ScaryJim's theory is correct then we should be walking on air, no? No need Air Nikes, centrifugal force, baby!

[scaryjim]

If ScaryJim's theory is correct then we should be walking on air, no? No need Air Nikes, centrifugal force, baby!

When did I say anything that could be construed that way? I'll happily take refutals of my science, but please don't make up ridiculous nonsense then try to put it in my mouth...