Wheel momentum Walter Lewin
Why Physics Stack Exchange recommends it
Physics Stack Exchange users link it as a visual demonstration of gyroscopic precession whenever questions involve spinning wheels, torque and angular momentum.
Recommended by 5 people across 5 different months, 2012 to 2023.
What it is
A 3-minute clip from Walter Lewin's MIT OpenCourseWare physics lecture demonstrating a spinning bicycle wheel suspended from a string, which precesses instead of falling. It shows how gyroscopic precession works and how adding mass changes the precession rate.
What people said
Recommends Jaime · 2012-09 · Physics Stack Exchange · on “What happens when I roll a gyroscope along its axis of spin?”
There really isn't, any mechanical work involved. It is similar to what happens if you push really hard against a wall: you get tired, but without doing any actual work. See, when you apply torque to your gyroscope, you do it applying a couple [LINK] , i.e. two displaced, equal but opposite forces. You may e.g. push the top of the rotation axis to the right, and the bottom to the left. When you do this, the gyroscope will start tilting perpendicularly to the forces applied, e.g. in the front-back plane in the example above. If you apply your couple in the right direction, you can tilt the axis of rotation almost effortlessly. But the movement is so counter-intuitive that you normally apply m
Recommends Ryan · 2014-04 · Physics Stack Exchange · on “Torque and angular acceleration with bicycle wheel”
This might be a simple problem for many of you. However, please help me understand it too. I have been looking trough a lot of materials online, and I still have the following questions, that would help me a lot. I saw this video on youtube: see wheel in action [this video] If we consider the following model: Please clarify for me the following questions: I believe the gravity is not pulling the wheel down because the torque resulting from multiplying gravity by the l vector is pointing sideways. In other word, the down-pointing gravity vector is transformed into a vector pointing sideways and spinning the wheel around the string. (Is this how force multiplication works? do the multiplied factors
Recommends Farcher · 2017-01 · Physics Stack Exchange · on “What gives energy for precessional motion of gyroscope?”
The centre of mass of the rod and the spinning disc drops a little. Thus there is a loss of gravitational potential energy and a gain in the precessional kinetic energy. You can think of it as the torque which is causing the precession rotating through an angle and so work is done by the torque which increases the rate of procession. The change of angle of the rod is small and so the effect is difficult to see. If you watch this Walter Lewin video [this video] at 2:30 he releases the gyro. Does the inclination of the rod change? At 2:40 a mass is added to the rod which increases the precessional kinetic energy and hence the rate of precession and there is a definite change in the angle of the rod
Recommends Victor Palea · 2017-08 · Physics Stack Exchange · on “How can I determine the rpm of a wheel that's spinning really fast?”
My take on this question is based on this video [this video] . The idea behind this is that if you manage to transfer the angular velocity from the motor to a spinning disk and create the setup from the video, you can, based on the geometry of the setup and the precession velocity, calculate the angular velocity of the motor. The calculation can be found here [LINK] , pages 4-6, problem W14D3-2 Table Problem Suspended Gyroscope Solution . At the end of the problem you have the following formula where all the parameters are defined in the document: $$\Omega=\frac{d\cdot m\cdot g}{I_{cm}\omega_s}$$ For your scenario, you can use the above formula, but to compute $\omega_s$ by measuring $\Omega$. I
Recommends user267839 · 2023-07 · Physics Stack Exchange · on “Spinning Wheel subject to Gravitational Force”
I have a question about the dynamics of a horizontally suspended rotating wheel subjected to the gravitational force, like in the following picture I took from here [LINK] : [LINK] At the beginning, the wheel has an angular momentum $\vec{L}:=L \vec{e_x} $ in the horizontal plane, which coincides with the axis of rotation (considered as the initial condition before the gravitational force starts to act). Then, we let the gravity act on the wheel, and we observe that the wheel axis performs a precession movement on the horizontal plane. For the sake of completeness, here's a video [this video] discussing it. The theory says that gravity exerts torque $M \vec{e_y}$ (directing into the drawn 2d plan
Cites Feynmanfan85 · 2019-05 · Physics Stack Exchange · on “Why aren't electrical power generators housed in "floating" structures that would allow them to spin?”
Every generator I've ever seen is housed in a fixed mount, and uses a rotating magnet in a column, powered by something like combustion, or wind, to generate a current through Faraday induction. But if you have rotational motion, you get spin acceleration that is orthogonal to the original rotational motion, "for free": [this video] I was wondering if there are generators that use floating columns to take advantage of this additional acceleration. If not, why? Is it not enough acceleration to justify the added complexity? It's a weird property as a general matter, and it depends upon the mass of the rotating object, even if less than all of the mass is rotating. E.g., if you hang a weight from a