As of May 31, 2023, we have updated our Code of Conduct.

# Tag Info

Accepted

### Why does a spinning top get back upright when knocked?

The torque that rotates a top upright, as happens in that youtube video, is due to sliding friction between the top and its supporting surface. Crucial to this effect is the fact that the top in that ...
• 7,581
Accepted

### How to tell if an orbit is closed given the potential?

It is not enough to have $r(t)=r(t+\Delta t)$: you must simultaneously have $\phi(t)=\phi(t+\Delta t)$ where $\phi$ is the angular degree of freedom. To put it differently, your need the radial and ...
• 42.9k
Accepted

### Newtonian contribution to perihelion precession of Mercury

You are essentially correct to assume that the precession is sometimes backwards as well. The frequently quoted value of 531"/cy is only the long term net average. In reality there is a ...
• 1,966
Accepted

### Does motorcycle counter-steering work by precessional motion?

A precessing effect might be there, but it isn't necessary. In order to negotiate a turn you need to initiate the lean first. To obtain a lean to the right you need to steer the contact patch of the ...
• 18.4k

### Antigravity force in powered precession gyroscope

This scheme gets invented every 20 years or so and then gets promptly disproved both by experiment and by dynamical analysis. For example, I thought that I had invented this very scheme with my ...
• 83.8k

### Details of Newtonian Prediction for Mercury's Precession

The Newtonian Mechanics prediction for the Mercury's Precession is actually $532''$ per century. The general result If the central force is attractive, there is a circular orbit of radius $r_0$. ...
Accepted

### 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 ...
• 86.8k
Accepted

### Without using rotational mechanics, why does a gyroscope precess the direction it does?

The reason why a gyroscope does behave in this strange way is that if you try to rotate it's axis in some direction, the "endpoints" of this axis have to be pushed perpendicular to what our first ...
• 1,201
Accepted

### How was the neutron's spin measured?

The spin of the neutron was measured by the Stern-Gerlach experiment by Sherwood, Stephenson and Bernstein (1954) (sadly paywalled, free links welcome), Abstract: A neutron beam was polarized by ...
• 26.6k