# Will a precessing spinning wheel fall down if there is no friction at all?

If there where no friction at all, would a spinning wheel held up by one end of the axis spin precess forever without falling down? Direction of torque precession of a spinning wheel

Since it seems to be a good practice on stackexchange not to ask several questions in one post, I splitted them up into two questions. However if I am wrong, feel free to merge this questions.

• If there were no friction at all and the wheel did fall down, where would the energy in the spinning wheel have gone? – Peter Shor May 5 '12 at 14:05
• @PeterShor The wheel just continues to spin. – martin May 5 '12 at 14:50
• So the spinning would speed up to compensate for the loss of gravitational potential energy in the wheel? I suppose that wouldn't violate conservation of energy, and angular momentum isn't locally conserved here anyway, so maybe you do need to use some actual physics to get the right answer. – Peter Shor May 5 '12 at 15:24
• Actually this is a very good case for having two separate questions. – David Z May 5 '12 at 15:27
• – Qmechanic May 5 '12 at 18:53

$$\frac{\text{d}\vec{L}}{\text{d}t} = \vec{\tau}$$
$$\frac{\text{d}\vec{v}}{\text{d}t} = \vec{a}_\text{cp}$$
• Hm, this should be also the case for a very very small $\omega$, seems to be very unintuitive for me – martin May 5 '12 at 19:19
• First step is understanding without thinking about $\omega$. If you want $\omega$ in the picture you should use Euler's equations, because $\vec{L} = I \vec{\omega}$ is valid only for fixed axis rotations (and of course along principal axis of moment of intertia too!). It can become extremely complicated to understand things when Euler's equations are considered. – Pygmalion May 5 '12 at 19:30