Cemtrifical motion? Symtriphical? Simtrifical? Can someone help?
Centrifugal is the misnomer you’re looking for.
Centripetal is the proper term.
Well, there’s centrifugal force pulling you outward as you spin, and centripetal force pulling you inward. Take your pick.
Centrifugal
To clear up what may be some confusion on the application of the term –
Centrifugal force is the term describing what feels like a force throwing you or something else out of a circle you’re rotating in. Centripetal force or centripetal acceleration is the term for acceleration while undergoing circular motion, which is always inwards towards the center of the circle.
Centrifugal force is imaginary in a technical physical sense. A force is something that works into Newton’s Laws of Motion :
- Things don’t change their motion (stopped or otherwise) unless a net force is applied.
- Things go faster the more net force you apply, and
- For every action there’s an equal and opposite reaction.
When something’s spinning in a circle, the centripetal acceleration is what keeps it spinning instead of flying off into space. As it spins, it’s always heading out of the circle, so it must constantly make a turn in toward the center. This is why centripetal acceleration is inwards.
Example: You’re driving (or riding) in a vehicle going straight and the road ahead curves. You must adjust the steering wheel as you move completely through the turn. If you were to set the steering wheel straight ahead at any point, you’d go off the road to the outside of the turn.
So why do we feel centrifugal force? That’s just one of the unexplained mysteries of the cosmos. Well, no actually. Centrifugal force is the force you feel as a reaction to the centripetal force (Law #3). Your body wants to keep moving straight out of the circle, and whatever is making you turn forces you back in. The reaction of your body to this is what we call centrifugal force.
The term “centrifugal force” is no more a misnomer than the term “gravitational force”. It all depends on what coordinate system you’re in. If I’m standing in line for that ride that spins around and drops the floor out from under you, and I see a person squished against the wall, then I’ll say that the person is trying to move in a straight line, but that the wall of the ride is pushing against the person, causing them to move in a circle and squishing him: This force exerted by the wall on the person is the centripetal force. Now, suppose I get on the ride myself, and find myself squished. In my personal coordinate system, I’m not moving, so I can’t explain this in the same way as when I was outside of the ride. Instead, I say there’s a centrifugal (literally, “fleeing the center”) force pushing me agianst the stationary wall. This force isn’t exerted by anything in particular, but it most definitely is exerted on me.
If it sounds like cheating to change referece frames like that so a force magically appears from nowhere, it might help to know that in the context of General Relativity, the modern theory of gravity, gravity is also considered to be a fictitious force, which just seems real because of the curvature of space.
Centrifugal EFFECT, not force. It is not a force, the only forces are the one holding you to the object you are orbiting and the force driving you around it. The centrifugal effect is just your intertia, you want to move in a straight line but are being forced to curve, so it feels like something is pulling you outwards.
Thanks, Badtz, I was gonna mention this. Further, I’d like to add that the centripetal force is not a generative force of its own accord; it must be supplied by something. For example, a planet revolving around a star is held in that orbit (centripetally) by mass attraction. For a penny on the edge of a record (remember those?) it’s friction. This is why when you turn you “turn table” up from 33 1/3 to 45 to 78 (history lesson) the penny flies off. The linear force (applied to the penny via the record at that radius) is ever increasing with angular velocity (sort of) until the friction force is overcome.
Tried to keep it simple so as not to be labeled “verbose”.
Of course, the “Centripetuge” I invented for separating liquds and solids in suspension never took off.
Me too. Especially since this was a spelling question.
I’m a little bit rusty, Chronos, but from your reference frame, isn’t the centrifugal force actually the normal force of your body?
When I’m being ‘forced to curve’, what is the force that is curving me? Centripetal force. Without a centripetal force and thus a centripetal acceleration, I depart the merry-go-round.
Remember, for every action there is an equal and opposite reaction. If I stare into the abyss, the abyss stares back into me. If the merry-go-round pushes me to keep me going in a circle, I push back. Centrifugal effect, force, whatever.
And, as Chronos pointed out, the same can be said of gravity. “The gravitational effect is just your inertia, you want to move down the curved space-time but are being forced to stay still (due to the earth being in your way) so it feels like something pulling you downwards.”
What does that mean? “Gravity is not a generative force of its own accord - it must be supplied by something (curvature of the earth.)” “Electrostatic repulsion is not a generative force of its own accord - it must be supplied by something (the charges of the particles.)”
What force is a force of its own accord? What does that even mean?
‘Just’ is perhaps an interesting word. First, unless I’m misunderstanding you, the ‘normal’ force refers to the component of the force vector that is perpendicular to a surface. In the case of a penny on a turntable, the normal force is constant with RPM, because the surface is at right angles to the axis of rotation and thus there is no component of centripetal or centrifugal force normal to the surface. Yet, the penny flies off the LP.
Next, the same thing applies to gravity, if you want to bring ‘just’ into it. Remember, a linear acceleration is indistinguishable from gravity in relativity. The only difference between gravity and centrifugal force is that if the radius of your circle is small enough you can tell by the gradient of force and other forces (e.g. coriolis) that you are under a rotational frame and not a linearly accelerating or gravitationally influenced frame.
Really? Curvature of the earth? 
“Just”? Did I say that?
I did say I was rusty. I took dynamics in college, but not statics… What’s the term for the opposing force that holds an object in place? That is, if the a book pushes on a table with a “gravitational force”, what is the name of the force that the table pushes up with? (ISTR always calling it the “normal” in my physics classes.) If wall of the Wheel O’ Death carnival ride pushes your body in with a centripetal force, from the bodies’ point of view, doesn’t the body push out with a normal force? I could be wrong.
Expanding a bit:
Earth’s elliptical path around the sun derives from the interaction of two forces: The centripetal (center-seeking) which, as correctly pointed out by spritle, pulls Earth into the Sun, and the “tangential force” which, as a result of Earth’s momentum, acts to keep Earth moving in a straight line, that is, in a direction perpendicular to the centripetal force generated by the Sun’s gravitational pull. The resultant force of this cosmical “tug of war” is what restricts our planet to follow its elliptical orbit round and round the Sun.
What do I want for X-mas? A centrifuge, of course. 
Errr… There is no “tangential force” except for the possibility of a tiny drag as the earth pushes through the solar wind. Earth has a tangential velocity vector, which is constantly changed in direction due to gravitational force. a = F/m. The earth exerts an equal and opposite gravitational pull on the sun, but there are no tangential force vectors associated with the sun’s gravity in this situation.
Going back to the Gravitron ride…
If the wall is exerting Centripetal force on you towards the center of the circle, wouldn’t you be exerting Centrifugal force back against the wall (perhaps just another name for the Normal force)? Isn’t that one of Newton’s laws? Equal and opposite reaction.
Yes, that is what’s happening (at least that’s how I understand it). I’m only agreeing with what I said earlier, though. I just wanted to quote the song.
mrblue92 – I think if you call it a ‘reaction force’ you won’t have a problem. Then again, I think ‘normal’ may be correct too, but I didn’t pay close attention in statics.
mrblue92, a “normal” force is any force acting perpendicular to a face. Typically this is applied in statics and dynamics to reaction forces because of gravity or other forces.
A more appropriate term would be reaction force.
In the carnival ride, the reaction force is inertia.
The “equal and opposite reaction” line is one of the most misunderstood principles of classic physics. What it means is that forces act in two directions, or between two objects. You can’t push on a wall and the wall not push on you. It does not mean I push on a door and the door will open. It means I push on the door, and the door pushes back.
Separately, there is a reaction that is the door opening, due to the imbalance in the forces on the door. But that reaction is not the reaction that Newton meant.
This is getting into a question of semantics and definition, but in all the usage I’ve seen, the centrifugal force is not the force of the person on the wall of the ride (or whatever). It’s the force of nothing in particular acting on the person, in the non-inertial reference frame. Perhaps a better example: You’re driving along in your car, and go around a sharp turn. You’re pushed over to the side (at least, with respect to the reference frame of the car). What is the force that’s pushing you? The centrifugal force. In this case, there aren’t necessarily any “real” forces acting in the sideways direction.
Oh, and “normal force” and “centripital force” are two independent concepts. Normal refers to how the force is being produced (by two things in contact pushing on each other), while centripital refers to what the force is doing (causing something to move in a circle).
Yes, that’s actually what I was referring to by saying it was a “misnomer”. Maybe I should have been more specific. Too busy in MPSIMS lately…
At least I got the spelling part right.
You misunderstood my post, mrblue92.
A quick outline of what I meant:
The Sun gravitationally pulls Earth into it. We call that gravitational force centripetal. That term refers to the direction of the applied force, not to its nature.
Were there not another sizeable force acting upon Earth it would plunge into the Sun ala Icarus. Some force must be exerting its influence to prevent such a chaotic scenario.
I called that force"tangential," to refer to the fact that it directs Earth into a trajectory tangential to its orbit. It is a result of Earth’s inertia and thus prompts it to follow a straight line, in a direction perpendicular to the Sun’s “gravitational seduction.”
This perpendicular forces result in a force vector that follows an almost circular, elliptical path around the sun.
Hope that clears it.
Writing this, two questions arose.
Regarding the “controversial” tangential force:
Technically, it shouldn’t be considered a force since it is not producing an acceleration on Earth, it is only a result of its inertia, right?
Second, is this so-called force a carryover from the angular momentum gained by Earth as it formed and started to revolve around the Sun? I am pretty sure it is, I am just not very clear on the details surrounding Earth’s genesis.
Right now, the Earth is pulling on me gravitationally with 170 lbs of force. At the same time, the chair I’m sitting on is pushing up on my butt with 170 lbs of force. Now, the first force has a definitive source: gravity. But what is the source of the second?
Centrifugal force is a force in much the same way. It’s the equal-but-opposite force reacting to the centripital force.