Spin Needles in Gravity-less World: Does It Work?

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In summary, the conversation discusses the possibility of making a stationary needle spin in a gravity-less world without friction. The method proposed involves flicking the needle to cause it to twirl, then tapping its ends repeatedly to transform the twirling motion into spinning. One version of the problem also involves using an accelerating funnel to force the needle to rotate, while another version involves tapping the ends of the twirling needle in a specific way. There is disagreement between the speaker and an expert on whether the needle would spin or continue twirling after these actions. The speaker provides a qualitative analysis of the motion of the needle in both scenarios.
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hkyriazi
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In a gravity-less world without friction, starting with a stationary needle, would one be able to make it spin by first flicking it, to cause it to twirl (so that its axis of rotation is perpendicular to its long axis), and then tap its ends repeatedly in some way so as to cause the twirling motion to transform into spinning (i.e., so that the axis of rotation is lined up with the needle's axis)?

(I posted a long and somewhat involved variant of this question on the "homework/introductory physics" section over a week ago -- though it's not a homework problem -- without getting any response. It was titled "A simple rotational problem." I thought that posing it in this simpler way, I might at least get a comment or two.)

One possibility would seem to be to have the twirling needle be scooped up by the wide end of an accelerating funnel, so that, in effect, the needle would be "going down the drain," making a series of reorienting, frictionless contacts with the sides of the funnel. Let's say the funnel approaches the needle so that its axis of symmetry is almost (but not quite) lined up with the needle's angular momentum axis (off only a bit, so that the needle doesn't get lodged in the funnel).

The question is, when the needle comes out of the funnel (whose bottom is just barely wider than the needle), so that its own axis has been forced to rotate almost 90 degrees, so as to basically line up with its original angular momentum axis, will it be spinning?

I say yes, and that it'd be spinning much faster than it twirled, owing to the much smaller moment of inertia in this orientation. But, I have an expert who disagrees with me (Professor Eugene Butikov, of the Univ. of St. Petersburg, Russia), who says the needle would have zero spin about its long axis, and would immediately go back to twirling, but at an angle determined by the last contact it makes as it leaves the funnel.
 
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In another version of the same problem, I posited that one merely tap the ends of the horizontally twirling needle, such that when it's floating right in front of one's face, one lightly taps the left tip downward, and the right tip upward, so that one imparts a relatively small torque that points right at you, and at right angles to the needle's initial angular momentum.

The question is, what is the motion of the needle after those light taps?

If one considers oneself to be rotating in the same frame as the object, so that the object appears stationary, ones taps would obviously cause the needle to twirl counterclockwise with its center of mass stationary. The top side of the needle would flip over and back once with each vertical rotation. The inertial frame's horizontal twirling has the top side always up, and so when one combines these two motions -- a strong horizontal twirling and weak vertical twirling -- the main motion must still be an approximately horizontal rotation, but now where the top of the needle rotates to the bottom and back up periodically, which means the needle must be spinning about its axis, which means it must also be precessing somewhat.

Does this seem like a reasonable qualitative analysis to anyone besides me?
 
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The question of whether a needle can be made to spin in a gravity-less world is an interesting and thought-provoking one. It raises a number of interesting concepts and principles in physics, such as angular momentum, moment of inertia, and frictionless motion. Let's explore this question further and see if we can come to a conclusion.

First, let's establish some basic principles. In a gravity-less world without friction, a stationary object will remain stationary unless acted upon by an external force. This means that the needle will not spin on its own, and some external force must be applied to make it spin.

Next, we need to consider the concept of angular momentum. Angular momentum is a measure of an object's rotational motion, and it is determined by both the object's moment of inertia and its angular velocity. In a frictionless environment, the needle's moment of inertia will not change, but its angular velocity can be altered by external forces.

Now, let's consider the proposed method of making the needle spin. Flicking the needle will give it an initial angular velocity, causing it to twirl. Then, tapping its ends repeatedly could potentially cause the twirling motion to transform into spinning, with the axis of rotation lined up with the needle's axis. This method relies on the principle of conservation of angular momentum, where the total angular momentum of a system remains constant unless acted upon by an external torque.

The idea of using an accelerating funnel to scoop up the twirling needle and force it to rotate almost 90 degrees is an interesting one. However, it is important to note that in a frictionless environment, the needle will not experience any torque from the funnel's walls, as there is no friction to cause it. This means that the needle's angular momentum will remain constant, and it will not be forced to rotate in a different direction.

In this scenario, the needle will continue to twirl, with its axis of rotation determined by the last contact it makes with the funnel's walls. It will not start spinning on its own, as there is no external force acting on it to change its angular momentum.

In conclusion, it is unlikely that the proposed method of using an accelerating funnel in a gravity-less and frictionless world will result in the needle spinning. The needle will continue to twirl, with its axis of rotation determined by the last contact it makes with the funnel's walls. While the concept of using external forces to alter the needle's angular momentum
 

1. How do spin needles work in a gravity-less world?

Spin needles utilize the principles of angular momentum and gyroscopic stabilization to maintain their orientation and direction of spin. In a gravity-less environment, there is no external force acting on the needle, allowing it to spin continuously without falling or changing direction.

2. Can spin needles be used to navigate in a gravity-less world?

Yes, spin needles can be used for navigation in a gravity-less world. By controlling the direction and speed of the spin, the needle can be used as a compass to determine the orientation of an object or spacecraft.

3. Do spin needles work the same in a gravity-less world as they do on Earth?

No, spin needles behave differently in a gravity-less world compared to Earth. Without the force of gravity, the needle will not experience friction or resistance, allowing it to spin indefinitely.

4. Are there any limitations to using spin needles in a gravity-less world?

One limitation of using spin needles in a gravity-less world is that they require an initial spin to maintain their orientation. Without this initial spin, the needle may have difficulty stabilizing and may drift off course.

5. What other applications can spin needles have in a gravity-less environment?

Aside from navigation, spin needles can also be used for stabilization and attitude control of spacecraft and satellites. They can also be used in experiments to study the behavior of objects in a gravity-less environment.

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