Easiest way to control current

WBahn

Joined Mar 31, 2012
24,849
Another option to reduce the swing amplitude would be to increase the pendulum bob weight.
Increasing the bob weight will increase the period of oscillation, which does not sound like what he wants to do. He just wants to decrease the amplitude of oscillation (which has very little impact on the period).
 

ebeowulf17

Joined Aug 12, 2014
2,945

Tonyr1084

Joined Sep 24, 2015
3,627
Increasing the bob weight will increase the period of oscillation
I was about to say this as well. However, I'm not sure that's the case. The reason why I refrained from this comment is because the weight may not be as important as the length of the bob. The longer the arm the slower the swing (longer the period). I think! Not certain though.

[edit] Thanks Wulf! Had to beat me to it; didn't you?!
 

WBahn

Joined Mar 31, 2012
24,849
Are you sure about that? I thought weight was unrelated to period. Online calculators I've looked at don't include weight. Here's one example:

https://www.omnicalculator.com/physics/simple-pendulum#how-to-analyze-a-pendulum-in-swing
For a "simple pendulum" this is true. But there are a lot of simplifying assumptions that are required to treat something as a simple pendulum - specifically that it consist of a point mass located at the end of a rigid, massless rod. That is clearly not the case for the pendulum in those movements the TS has linked. If you add mass, you are almost certainly going to change the location from the pivot to the center of gravity, and that it is the single dominant term in the period.
 

ebeowulf17

Joined Aug 12, 2014
2,945
For a "simple pendulum" this is true. But there are a lot of simplifying assumptions that are required to treat something as a simple pendulum - specifically that it consist of a point mass located at the end of a rigid, massless rod. That is clearly not the case for the pendulum in those movements the TS has linked. If you add mass, you are almost certainly going to change the location from the pivot to the center of gravity, and that it is the single dominant term in the period.
Interesting points - thanks for clarifying!

So, hypothetically it might be possible to reduce amplitude, without changing period, by adding mass at the exact same distance as the existing center of gravity... just as a theoretical exercise.
 

Alec_t

Joined Sep 17, 2013
10,424
Increasing the bob weight will increase the period of oscillation, which does not sound like what he wants to do.
It shouldn't affect the period much; but even if it did, does that matter? The pendulum is only decoration and isn't controlling the timing of the clock.
 

WBahn

Joined Mar 31, 2012
24,849
It shouldn't affect the period much; but even if it did, does that matter? The pendulum is only decoration and isn't controlling the timing of the clock.
I didn't catch that it was only for decoration. I thought it was so that you didn't have to wind up a main spring to power the pendulum. If it's just for decoration, then it doesn't matter as long as it's in the ballpark so that it "feels" right.
 

WBahn

Joined Mar 31, 2012
24,849
Interesting points - thanks for clarifying!

So, hypothetically it might be possible to reduce amplitude, without changing period, by adding mass at the exact same distance as the existing center of gravity... just as a theoretical exercise.
I think to a first order that's correct. The physics of a pendulum are actually very complex and, even in the case of a simple pendulum, mass does have an affect as a higher order term that can become noticeable once you have amplitudes that can no longer be considered "small".
 

crutschow

Joined Mar 14, 2008
23,480
The physics of a pendulum are actually very complex and, even in the case of a simple pendulum, mass does have an affect as a higher order term that can become noticeable once you have amplitudes that can no longer be considered "small".
I would assume air resistance would be a small part of that.
 

WBahn

Joined Mar 31, 2012
24,849
I would assume air resistance would be a small part of that.
Sure. And friction in the components. But both of those are usually well under the affect of a change in mass, particularly if it moves the center of gravity.

Other, larger, factors include the latitude and altitude at which the pendulum is located (as these affect the perceived gravitational constant) and the motion of the clock. I don't know how much the affect of latitude was understood at the time that John Harrison was working on his marine chronometers. But, if it was known, it's a correction that could be readily tabulated and kept track of during a voyage. As for the motion, that was one thing that Harrison discovered and that caused him to abandon one of his primary approaches and led him to use circular balances instead of bar balances.
 

Yaakov

Joined Jan 27, 2019
1,600
Still don't understand why no one wants to follow what the manufacturer of the device says?
I think the discussion has become theoretical. I would guess that any one to the theorizing parties would immediately follow the suggestions of the manufacturer, though to be honest, I don't really understand how tape would reduce magnetic fields, but I would certainly try it. The idea, that field strength reduction would do the trick, is enough. The problem would be solved one way or another.
 

WBahn

Joined Mar 31, 2012
24,849
Still don't understand why no one wants to follow what the manufacturer of the device says?
I don't know why you think no one wants to follow what the manufacturer of the device says.

In fact, I seem to recall someone very explicitly recommending that the TS look up what the manufacturer of the device has to say back in, oh, Post #6 or so.
 

shortbus

Joined Sep 30, 2009
7,074
I don't know why you think no one wants to follow what the manufacturer of the device says.

In fact, I seem to recall someone very explicitly recommending that the TS look up what the manufacturer of the device has to say back in, oh, Post #6 or so.
And Some one else found and showed it in post # 14 and #22. Smart guy.
 

WBahn

Joined Mar 31, 2012
24,849
And Some one else found and showed it in post # 14 and #22. Smart guy.
Agreed. And since you clearly knew this, it begs the question even more why you would then claim that no one wants to follow what the manufacturer of the device says.
 

Tonyr1084

Joined Sep 24, 2015
3,627
I would assume air resistance would be a small part of that.
My parents had a wind up clock with a pendulum. I can still hear it clicking twice per second. On the bottom of the pendulum was a screw jack that you could move the weight up and down to accommodate for making adjustments to keep the clock at the right time.

With pendulums made of wood, humidity changes things as does temperature. So there are a lot of factors that go into making a clock that can compensate for temperature and humidity, and that stuff is WAY over my slick head.

In theory you can have a heavy weight just inches down from the fulcrum and an arm that is 10 inches long (for example) and the period will be much shorter than if the bob weight were down at the 10 inch point.
 
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