Dancing T-handle in zero-g, HD

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Strong rec TimWescott · 2022-12 · Physics Stack Exchange · on “Does applying a series of torque forces to an object result in a constant angular velocity about a particular axis?”

Well -- no. Here's a particularly good example on YouTube [this video] . It shows a T-handle being spun along the intermediate axis of its moment of inertia, and then exhibiting spin instability by flipping the direction it's pointing, all while continuing to spin. The preserved quantities in this case are energy and angular momentum (with respect to the inertial frame of reference). But the spin referenced to any axis that you pin onto the object doesn't have to be constant. But you were close -- if you add up the rotational impulses that you impose on the object (basically the torque integrated over time), the result will be the angular momentum.

Recommends CR Drost · 2017-09 · Physics Stack Exchange · on “Under what conditions does the relation $\vec{L} =I \vec{\omega}$ holds good?”

To get a "handle" on this I love to show people the dancing T-handles in space videos [this video] . The orientation of the T-handle whips back and forth quite drastically, however one can see, if one looks carefully, that the angular velocity about that axis reverses sign whenever it does this, and it's reasonable to think that the overall angular momentum is roughly constant. But if you consider the transitions between these two opposite axes, the direction of $\vec\omega$ points along the axis of the T, so it must be pointing perpendicular to $\vec L$.

Recommends S. McGrew · 2018-04 · Physics Stack Exchange · on “How does spin flip take place?”

If you hang a spinning gyroscope from a string, with its axis perpendicular to the string, you can watch it precess. Take note of the frequency and direction of its precession. Now swing the top end of the string in a small circle at about that same frequency, first in the same direction as the precession and then in the opposite direction to the precession. The gyroscope will orient itself either up of down depending on the direction of your circle. This is a consequence of classical mechanics. Pretty much the same happens when the spin of an electron is flipped by an applied RF field. Here's what's going on. When the axis of the gyro is sticking out horizontally, it stays at pretty much th

Recommends Robert Graybeard · 2020-02 · Space Exploration Stack Exchange · on “What stability issues plague long artificial gravity cylinders?”

What is it exactly that would make longer designs more challenging to manage? I was looking for the paper that an acquaintance (Al Globus, the author of the Kalpana proposal) quoted when he defended the "stubbyness" of Kalpana in personal conversation. Google Search found your question instead of that paper. The tumbling of Explorer1 that Mark Adler mentioned was also mentioned by "Veritasium" in the YouTube video The Bizarre Behavior of Rotating Bodies, Explained . Note that "Veritasium" used the clip Dancing T-handle in zero-g, HD posted by "Plasma Ben". The Dzhanibekov Effect or The Tennis Raket Theorem or The Intermediate Axis Theorem The instability - or rather the tendency to reorient

Recommends Carmeister · 2022-01 · Physics Stack Exchange · on “What's the physics behind the jumps with seemingly non-conserved angular momentum?”

The thing that you're actually seeing in the video is the angular velocity, not the angular momentum. Unlike linear momentum and velocity which are related by a constant scalar, the mass ( $\mathbf p=m\mathbf v$ ), the angular velocity and angular momentum are related by the moment of inertia: $$\mathbf L = I \boldsymbol\omega.$$ The moment of inertia differs from the mass in that: it is a matrix not a scalar, so that the angular velocity and angular momentum need not point in the same direction, and it depends on the shape of the body, which means it can change if the diver moves his limbs around. Together these two facts means that the angular velocity need not be conserved even though ang

Cites Jack B · 2016-12 · Space Exploration Stack Exchange · on “Is there any safety advantage/disadvantage to a particular attitude of a vessel in space?”

Radiation As you have rightly noted, a long cylinder pointing end on to the radiation source (probably the sun, especially during periods of high activity), can be shielded by a smaller, and thus lighter, shield. On the other hand if you need shielding facing all directions, then a sphere is a better choice. (Micro-)meteorites The spaceship is moving fast, in some direction given by where it is, where it wants to be, and orbital mechanics. Dust, rocks and debris will be moving somewhat at random, but will tend to have a preferred direction. They mostly go round the sun/planet/moon the same way the rest of the solar system rotates, and there won't be many rocks on orbits which pass through an

Cites Luke Pritchett · 2021-06 · Physics Stack Exchange · on “Confusion on conservation of angular momentum”

This is incorrect, as you can see in this demonstration on the International Space Station. Even with no external torques the rotation of the T-handle is quite complicated [this video]

Cites Slarty · 2023-10 · Space Exploration Stack Exchange · on “How do you design a spacecraft with a spinning section for "artificial gravity"?”

It can all be managed, but its a lot more complicated than it might at first appear. Off center spinning objects in 0g especially with moving masses inside (people and stuff) do odd things: [this video]

Cites Zaph · 2024-03 · Physics Stack Exchange · on “Rigid body and angular motion”

If you have on object with some angular momentum the axis of rotation will only be stable if its rotating around one of its principle inertial axis and rotation would only remain stable after slight perturbation if its the principle axis with the highest moment of inertia. Consider a T-handle in outer space rotating around an axis, that is not its principle axis with the highest moment of inertia [this video] . Even though angular momentum is conserved, as there are no forces acting on the T-handle floating in outer space, its rotational axis does change over time and therefore: "a fixed axis, normal to the plane of motion, about which the line and the body rotate" does not exist.