Robittybob1

A paper towel roll would be easier to handle.

Spin it fast enough it will go over the edge of the cup.

I explored the maths of the situation today. When the scale at the end of the tube registers a force on it, the spring is compressed or stretched, either way, energy is added to the spring until the reactive centrifugal forces equals the centripetal force (the normal force provided by the scale. But the "push" does not push the ball back inward but allows the ball to travel in a circular path. The circular path it travels at is a larger radius that when the ball first contacted the scale. If the speed of rotation slowed the energy in the scale springs would push the ball back toward the center. You would need to keep the tube perfectly radial as you swing the tube.

When the scales I weigh myself I have to press on then first to get a reading. The spring inside gets stretched and then it reads my weight. Only as the ball pushes on the scale will the scale push back on the ball. That would be a rather easy experiment to check the physics. Are you saying that a centripetal force changes sign depending on which sector it is in. That is news to me. That does not sound right. Can you show me a link that confirms that please?

Is gravity a negative force too then? Why I said centripetal force is positive was that the formula Fc = m*v^2/r yields a positive value. Mass would normally be positive, v^2 would give a positive number whether the velocity was a negative or positive figure, and radius would the a positive value too. So how do you get a negative value to centripetal force? Reference to: http://www.scienceforums.net/topic/88420-centrifugal-forces-appear-to-act-opposite-to-gravity-how-is-this-possible/page-13#entry866983 Do you think if you blocked the end of the tube with a scale, and spin it up that the scale would not register any outward force? I'm picking there would be an outward force while the ball is in the tube.

If you rearrange Fcentripetal = N - mg you get Fcentripetal + mg = N Now when the mass is not moving wrt the coordinates mg = N Move mass wrt to coordinates and Fcentripetal > 0 (always greater than 0) Does mg stay constant? If so N force would increase not decrease as is the case by experiment. (Just within the ship) So do you think he will land ahead of where he jumped from?

When I looked at the definition of the Normal Force it was not always in the same or opposite direction as the gravitational force. So it maybe only a component of the normal force. http://en.wikipedia.org/wiki/Normal_force With your definition can the weight be calculated by (m*gr), that is the residual g force (gr) not accounted for by the centripetal force? What is the reason centripetal force reduces the effectiveness of the gravitational force? Looking at the title of the thread "Centrifugal forces ' appear ' to act opposite to gravity . How is this possible?" really you seem to have it "Centripetal forces ' appear ' to act opposite to gravity . How is this possible? So it was close!

I wasn't concerned about the motion of the object. I am trying to find out my own logical answer to why at suborbital speeds something weighs less. In the link you gave us your version of the answer but since you don't use the words "centrifugal force" I don't like your answer. It seems to be lacking something. Doesn't seem right. Since the gravitational force and the centripetal forces are in the same direction how can they use each other? Unless you are talking of the G force that the object exerts on the primary mass, the one I'm calling the centrifugal force.

1. Where would the nutrients go? 2. It sounds like filtration would concentrate the remaining material.

It must be locally for we don't worry about our speed around the Sun when doing kinetic energy experiments on Earth. Without a doubt we have the kinetic energy from the Earth's orbit too but when describe an object's inertia we can ignore speeds like these for we share the same coordinate system.

I have heard people say the force of gravity is the centripetal force, haven't you? So by some sort of logic since the centrifugal force is the equal and opposite to the centripetal force (which is the force gravity in these cases), logically the centrifugal force is equal and opposite to the force of gravity (and is the "reaction force to gravity" but gravity acting on the other body). I seem to have repeated myself but it follows a logical path. Like when the centripetal force is provided by the tension in a string I'm not saying that is gravity. I do appreciate what you say about "kinds of forces" (equal and opposite pairs are the same kind of forces). And thanks for the right terminology; "origin of the coordinate system". So does this mean an object traveling on Earth 1012 mph to the West at the equator will weigh the same as it did at poles? For at this speed it will be stationary wrt the origin of the coordinate system.

TAR - That must be the result of the toothpicks not being imbedded enough to stop the balls going off on their tangents. The picks embedded properly will provide sufficient centripetal force until the angular velocity rises even higher. It seems that at the limit where the mass moves along the tangent and separates from the circle there is an infinitesimally small radially outward motion. It is the summation of these movements that you see in the clay.

I thought I had the solution to this problem as I drove home, so what was it again? The OP title seems to ask a slightly different question as does the post, but from recollection the reason why something weighs less at the equator than it does at the poles was part of the problem. Someone said that is because the device used to weigh the object "is falling away from under it". I didn't like that answer to begin with but it could be a useful way of looking at it. When an object is orbiting another they say the gravitational force is the centripetal force, and we have agreed that the centripetal force is equal and opposite to the centrifugal force. So what is the equal and opposite to the gravitational force? Is it still the centrifugal force? Gravity works both ways to begin with. There is equal and opposite attraction between the objects. So as we have agreed the centripetal force acts on the object and the centrifugal force acts on the center, so the centripetal force acts on the orbiting object and the centrifugal force acts on the center (the primary mass). But this next bit seems the most controversial bit. Since the centripetal force is calculated using V^2 and I think that velocity is not a relative angular velocity but an absolute one, for you can't take the rotation rate of the primary into account. Did I get that right? PS: Absolute in the sense of the velocity being the distance travelled (2*pi()*r) divided by the period.

Why would it do that? Good point. But nothing can come in "from forever" as it all started in the Big Bang only 13.7 billion years ago.

Want wings? Join the airforce.

Not since I've started the thread, no. Does it mention about doubling the effect does it? I'll have another look. Once the ball is released no more forces act on it so as we established it must travel in a straight line, the dotted lines didn't show the path of the ball while it was held and as it was being accelerated during a throw and only straight after it is released.

Right. If it it isn't purely radial or tangential can it be a mix? Like simultaneously satisfying radial and tangential at the same time. In fact no YT physics lecture discusses "radial motion" otherwise I would have a better idea of the boundaries radial motion could have.

If "the target moves" the gun moves too doesn't it?

That was great thanks. Would that be described as throwing the ball radially inward from a rotating platform? The ball goes along a radius when it is not rotating, but when the turntable is rotating can you still see the effects of the tangential velocity? PS: Looking at it again, when viewing the ball from the camera back to the thrower (1:30 onward) you see the ball moving sideways with respect to the background. I couldn't see that he has accounted for the tangential velocity from the ground frame POV.

You said something like ""Increasing in radius" ≠ "radially outward motion"". There was "no change in angle" so are you saying you can't get radial outward motion from a rotating platform? I thought you could as long as the original tangential motion and outward motion simultaneously satisfied both situations where the mass has tangential velocity and the radius always aligns to the object.

I was hoping to find a video of a radially outward motion from a rotating disc, but I didn't find it, sorry.

OK, the point is while it was stationary there was no problem but when you rotate the turntable rapidly, will the target still be easy to hit?

I should have made it clear that while the merry go round (mgr) was stationary I had no problems in getting a bullseye on the target. It is on a very long extension horizontally out from the mgr. so the target rotates at the same rate as the mgr. I'm not going to go hunting with you. So I think you were describing a mounted gun firing at a ground based target. Well I wasn't trying to describe it like that, but more like that "radially outward" diagram you drew on the other thread. http://www.scienceforums.net/topic/88420-centrifugal-forces-appear-to-act-opposite-to-gravity-how-is-this-possible/page-12#entry866619 Very clever, so you mounted the target on the opposite side of the mgr and it still misses the target! If the bullet is fired outward into the playground The Mythbuster team showed the bullet from a rotating gun follows a straight path. But it can't leave the barrel at an angle, but it must take on the tangential motion of the gun. So it is not radially out and not tangential either. Can you explain it better please? http://www.discovery.com/tv-shows/mythbusters/videos/curve-a-bullet-minimyth/

It is a bit like what you get if you follow the point of a wheel rolling along the ground. Even though it is going around the point follows a series of humps in the horizontal direction. As traced by the blue curve in the attached YT video.

At the local playground on the "Merry go round" if you mounted a gun that would fire bullets radially outward and mounted a target to the whole system. Do you think the bullets will hit the target if the turntable was rotated rapidly? Kids stand back!