0
$\begingroup$

I'm having trouble understanding Foucault pendulum and from that I've extracted one of my doubt and here it goes:

A pendulum on a fixed platform is shown enter image description here

Now if we rotate the platform as shown

enter image description here

Will the plane of oscillation change or be the same? ( The suspension point doesn't coincide with the axis of rotation)?

Improve this question
$\endgroup$
2
  • $\begingroup$ The suspension is still relative to the moving table but the swinging pendulum isn't, does something come to mind? $\endgroup$
    – Karim Chahine
    Commented Feb 21, 2021 at 16:22
  • $\begingroup$ Thank you Dear Karim Chahine, won't the suspension point drag it now and possibly alter it's motion. $\endgroup$
    – Kashmiri
    Commented Feb 21, 2021 at 16:30

1 Answer 1

Reset to default
1
$\begingroup$

Actually, the idea for the setup we call 'Foucault pendulum' occurred to Leon Foucault in the following manner: he had clamped a long rod in the chuck of a lathe, he twanged it, and when he rotated the chuck the plane of vibration did not rotate. Foucault surmised that the momentum of the vibrating motion is not in any way bound to the physical orientation of the rod. In effect the momentum of the vibrating rod was behaving in accordance with Newton's first law. Unless acted upon by a force the momentum vector of a moving object keeps pointing in the same direction.

I did a search on youtube, and much to my delight I discovered a youtube video for this subject, titled: 'Scientic contributions of Leon Foucault', by dr Matt Nehring. Dr Nehring clamps the vibrating rod in the chuck of a drill

I assume that the reason that Foucault ended up with a gravity pendulum was that a gravity pendulum allows a setup with a large amplitude and large period of oscillation.

Any oscillation will have the property that the orientation of the momentum of the oscillation is not in any way bound to the physical matter that is vibrating.

The rotation state sensor in a smartphone has this type of rotation state sensing as its operating principle. It's not necessarily a vibrating rod, but some elastic part is oscillating, and the momentum of the oscillation tends to keep pointing in the same direction. (Depending on the build quality there will be some drift, but for the purpose of assisting navigation the sensors are quite sufficient.) The rotation state sensor in a smartphone is generally referred to as 'the gyroscope' but it isn't a gyroscope in the sense of consisting of some spinning wheel, suspended in gimbal mounting. The rotation state sensor of a smartphone is of the vibration type.


About why a larger Foucault setup is better:

The Foucault effect is very small, it's easily swamped by other effects. For instance, if the wire has a direction of bending where it is less bendable - and hence will have a direction of bending perpendicular to that where the wire is more bendable - then the force that tends to push/pull the pendulum bob back to midpoint will not be exactly the same in all directions, which would mean that the period of oscillation would not be the same in all directions, and that has the potential to swamp the Foucault effect. All the effects that unless prevented will swamp the intended effect are collectively referred to as 'parasitic effects'. In the case of a Foucault pendulum: the larger the pendulum, the less troublesome the parasitic effects.

Improve this answer
$\endgroup$
3
  • $\begingroup$ Why won't the rotating suspension point affect the plane of oscillation? I went to your website as well, it has great animations some of them in jar. format couldn't play those ones, but unfortunately I can't understand the basic point as mentioned above. $\endgroup$
    – Kashmiri
    Commented Feb 22, 2021 at 10:19
  • $\begingroup$ This is a 'choose your battles' type of situation. In order to proceed one must accept this as is. Many things can be explained, that's great, the deeper explanation can reach the better. But some things we have to accept as given, such as F=ma. That's why I'm delighted with the video of the presentation by dr. Matt Gehring. The rod swings with a wide amplitude, you hear the motor of the drill turning, and the orientation of the plane of oscillation remains the same. (It may be, I don't know, that the quantumphysical view does explain it. ) $\endgroup$
    – Cleonis
    Commented Feb 22, 2021 at 16:24
  • $\begingroup$ I don't know what to say Dear Cleonis,I thought an application of newton's law might reveal the fixed plane of rotation question but according to your view we can't? Am I getting it right? $\endgroup$
    – Kashmiri
    Commented Feb 22, 2021 at 16:54