Robittybob1

Thanks from http://isites.harvard.edu/fs/docs/icb.topic1216311.files/Project%20resources/Rolling%20sphere%20on%20turntable/turntablemodel.pdf That is nowhere enough compared to the results I was getting yesterday, so the two situations are a bit different.

Couldn't read the link without paying! Frustration! I hope you taught them how to spell as well "Coriolis".

There was a YT of the planned mission to Mercury by NASA. This could be the link

As I dosed off last night I thought spinning a friction free air track could be the way to go for then the rate of rotation would be much slower and hence easier to time. If one of those was mount horizontally but radially to a circle and the spun it slowly in a circle. Would the glider move along the track? Measure its speed at the time it hits the end of the track. Do a vector analysis of the two speeds tangential and radial. Estimate its path if it left the system. Can't wait to see this.

Looks like I'll have to try and run the experiment again in a way I can take accurate measurements and see if I can explain it with maths. This is a bit tricky as I don't have laboratory equipment that I'll need. Are there any students out there?

Didn't Swansont say inertia is not a force? I have heard of people talking about inertial forces but I wasn't sure if that is right though. So these inertial forces need to be opposite direction to the centripetal forces then. Which is possible for the difference between going in a straight line and going in a circle is a change in direction - inward toward the center. I did the experiment and the motion was not strictly tangential. So I would say there are other factors involved that you don't know about. Can you give me an example? Are you thinking of a pulley with a belt running around it? As to whether a force does work that would depend on the change of distance. A static centripetal force doesn't do work as far as I know but there would be work done slipping against friction (and that was a centripetal force.) Yet it is the centripetal force that makes an object moving in a tangential direction travel in a circle!

I've just come in from the experimentation and the mass definitely leaves the tube at an angle to the tangent, somewhere between the tangent and the radial depending on the rotational velocity. This was observed and confirmed by my friend as well. (Something like as if it is leaving at a tangent to a smaller circle earlier in the rotation.)

From a hunting point of view goats up a tree would be an easy target.

Did you look at those YTs on centrifugal motion? When the weights are close into the center of rotation there isn't the required velocity to orbit at the larger radii. There has to be an acceleration in the YT (and in our case within the tube) . That acceleration will take a force, it increases its tangential speed as it moves outward to keep up with the walls. It is in the tube so it can't go slower than the wall true, but it still has to speed up as it moves away from the center. You seem to agree with that. You agree that that acceleration is going to require a force? (your words "the walls need to exert a force to speed it up" but before that you say there is "no force".) I was showing how much force will be required to stop it on its outward path. It will take a force as large as its required centripetal force (calculable using mv^2/r) to make it attain a circular motion. I tested that ratio to the tangential speed many times in an Excel spreadsheet, and I graphed radius to the centripetal force. As the radius increases the required centripetal force increases linearly too. Friction between the wall and the mass is constant. So the ratio of Fc:Friction is not constant. Speed is proportional to radius at a constant omega (w). That part is definitely right. Today I hope to observe the angle the mass exits the tube by experiment. Is it tangentially (Swansont) or at an angle to the tangent as I suspect? I think we can see "the angle to tangential" effect with the last ball as it rises to meet up with the others. (1:36 onward.) Look at how the last ball rising up the incline catches up to the others. The balls don't just keep on rising up out of the bowl either. The inclined slope and gravity combine to provide the force to stop their outward motion at that rotational speed. I didn't see you try and explain what overcomes the friction. Thought experiment: You're sitting on a stationary merry-go-round and then some kids come and start spinning it. Your friction allows you to stay on to begin with but later you begin to slide. What pushes you? Now I'm asking you the same question as you asked me. What force overcame the force of friction? It is not the centripetal force; for friction is the centripetal force.

We both agree it will progress "radially" spiralling along a path up the tube. What pushes it? Obviously it must be the lack of the centripetal force, for it would need that to travel in the circle. Friction will provide a meagre centripetal force but soon the inertia overcomes the friction and it begins sliding along the tube. Gaining speed tangentially and radially, nothing pushes it but the motion itself can be concentrated into a fluid pressure as in a centrifugal pump. The reason it gains speed tangentially is because it is going slower than the walls of the tube at the ever increasing radius. The reason it speeds up radially is that even though the tangential speed is proportional to the radius the force required to it make travel in a circle goes up too but the friction stays the same so the ratio of friction:required centripetal force decreases.

Forces on inclined slopes ... mean forces and surfaces can meet at any angle and still yield some sort of analysable result. Your tube could be facing some degrees forward of radial and your lizard might still climb out of the tube. This was the principle off a juice extractor that I invented. I got someway through designing working prototypes before having to can the project. Some rotary juice extractors use centrifugal motion an inclined sieve but mine used on forwardly inclined curved sieves that rotated like the vanes of a centrifugal pump. (but in a centrifugal pump they usually curve backwards of the direction of rotation.

Swansont showed us what radial was but what is radial in a rotating system? One would think it would mean that the rotational rate is not changing as the point moves further from the center. This could be described as a spiral, but it would be a special type of spiral (and I don't have the terms at my fingertips).

That is a weird question.

The tube keeps the mass going at the same omega (rotational velocity). As it travels outward it is being accelerated by the tube but only in a tangential direction. It needs a centripetal force to hold it in a circular motion but the mass's centrifugal force, that would have acted at the center, is not attached to the center, so it accelerates the mass to the exit end of the tube. Here it can no longer accelerate. When it leaves the direction will be a result of the addition of the two velocity vectors. Same must happen on a merry go round as you slide outward you will be accelerated to a higher velocity at the larger radius as you get closer to the edge. At the edge your final velocity will depend on the ratio of the two velocities. A different situation applies if there is a string under tension. If the rotation (or circular motion) is enabled via a string, the string providing the required centripetal force and the string then is instantly cut, the mass has no way of accelerating further and the only velocity it will have is the instantaneous tangential velocity. It will have a spiralling motion within the system which is why when it leaves it won't be leaving tangentially as you say.

It won't work.

Are they from a human? They definitely aren't tibias.

is where I found it. Quite a messy presentation though. That was ok but the direction of the "sliding off" was incorrect. You move in the tangential direction but you slide off in the direction opposite to the centripetal force i.e. the "centrifugal force" or as I prefer now in the direction of the "centrifugal motion" As I see it since the mass has a tangential speed and a speed of moving from the inner part to the extremity of the tube, so it has a combinational velocity of those two. The ultimate direction it leaves the system is not purely tangential or radial but at an angle away from the tangent.

I did a search for the words centrifugal motion and came up with this animation. "Centrifugal Motion Demonstration" I'll have to think about it a bit more. Another interesting one "Tangential Force (centrifugal motion) on Fluid Demonstration IV".

Thanks, so we are both expecting the same thing in that the mass will move along the tubes and be thrown out in a direction that is a combination of their tangential speed and the speed they climbed the tube. We might be able to see that direction during the experiment. So to stop the ball rising in the tube we would have to apply a force to stop that motion wouldn't we? What would you called that force? If it was a piece of string you might call it a centripetal force. If you blocked the end of the tube you might call it a normal force. These forces are acting against an opposing force. Those masses wont travel in a circle unless there is a sufficient centripetal force. So when we say they are thrown out by centrifugal force but is it just centrifugal motion?

Could they be the bone from the phalanx of canines? They look like the bone that is in the claw of a dog. But you wouldn't call a 5-6 year dog a juvenile???

If I mount a piece of tube onto a central pivot and spun it with an electric drill. If then I stop it and insert two cylindrical masses one into each end of the mounted tube and push them right down to the pivot and then started up the drill again. Do you think the weights will be flicked out of the ends of the tubes? I didn't suggest marbles or ball bearings as they would roll too easy but these masses will take a bit of force to make them move along the tubes. The only centripetal force would be the friction along the tube, so the "centrifugal force" only needs to overcome this resistance. Even if I tipped the tubes up at 45 degrees angles I think the masses would climb the inclines! In this alignment they would have to overcome friction and gravity. So before I run the experiment would you care to predict what your physics allows?

I looked up the definition of G-force, for I think what I will be weighing in my experiment could be a similar effect and it said G-force is not a force but a weight. Weight is what I can read on the bathroom scales. http://en.wikipedia.org/wiki/G-force Does G-force and centrifugal force have a similar origin? I've got to define the weights, accelerations and forces better first.

That would be due to the addition of force vectors surely? I thought you might say that!

Sounds like it is time to do an actual experiment. Hypothesis to be tested: The scale is providing a centripetal force on the ball, so the ball must be applying a centrifugal force on the scale. Setup proposed horizontal Rotating tube with a bathroom scale attached. (The reason to do it horizontally is so gravity would have any net effect on the result.) Rotate it at 10 Hz. See what the scale reads Put soccer ball down tube and re-spin the tube at the same rate, take another measurement. Example please.

How long was the tube? How did you get the tube to shake at 40 hertz? That is 80 stops and starts per second. I doubt if you could do that manually. When the G force equals the centripetal force (Fcp). Fg = Fcp or Fg - Fcp = 0 A minus centripetal force has the same value as the reactive centrifugal force (Fcf) Fg + Fcf = 0