What is the cause of the slow movement of a large ice floe on a lake?

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Discussion Overview

The discussion revolves around the causes of the slow movement of a large ice floe on a lake, as observed in a video. Participants explore various hypotheses related to the mechanics of the movement, including the influence of wind and water wave interactions, while also questioning the observational details presented in the video.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that the ice floe appears to move back and forth within a small range, suggesting that its movement may be linked to water movement, potentially driven by wind pressure.
  • Another participant expresses skepticism about the periodic motion of the ice floe, questioning the accuracy of the measurements and the observational setup of the video.
  • There is a proposal that if periodic motion exists, it could be attributed to wind-driven oscillation that involves water wave motion.
  • A participant wonders if the restoring force acting on the floe could lead to simple harmonic motion, questioning how this would occur.
  • One participant suggests that thermal expansion and contraction due to sunlight might also contribute to the movement, especially on a calm day, while acknowledging that wind could introduce additional factors.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the cause of the ice floe's movement. Multiple competing views are presented, with some participants supporting the idea of wind-driven oscillation, while others question the observational details and propose alternative explanations.

Contextual Notes

Participants highlight limitations in the observational data, including the lack of fixed references for measuring movement, uncertainties about the filming conditions, and the potential influence of environmental factors like wind and sunlight.

Who May Find This Useful

This discussion may be of interest to those studying fluid dynamics, environmental science, or anyone curious about the interactions between ice and water in natural settings.

A.T.
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Here is a video of a large ice floe (~70x140m) moving visibly back and forth within a ~30cm range at ~1cm/s. The floe covers only half of the lake, but that almost completely, except a ~1m wide strip at the shore. At the end of the movie the camera pans to show the size of the floe.

What causes this movement? The ice is melting and probably quite thin. But still, the floe must weight tons. I think it can only move, when the water moves too. Is there some slow wave mechanics caused by wind pressure on the ice?

https://www.youtube.com/watch?v=6dRe_TFKt84
 
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I find it difficult to discern periodic motion of that ice floe from the video. There seems to be no fixed reference to use. How have the figures “~30 cm range at a ~1m wide strip” been arrived at? Which azimuthal direction is that movement in? Where in the image was this measurement made? How was the camera mounted? Was it fixed, or hand-held? At what altitude was it filming from? The zoom out process seemed unsteady so that this viewer had no idea of the eye height above the ice floe without any size reference. What is the depth of the lake? Which direction was the wind from?

Assuming that there was a periodic motion as you describe then I think that your proposed cause is plausible: wind-driven oscillation that includes water wave motion.

Cheers, Bobbywhy
 
Bobbywhy said:
Assuming that there was a periodic motion as you describe then I think that your proposed cause is plausible: wind-driven oscillation that includes water wave motion.

Would the restoring force then be the force of the water on the floe? How would that create simple harmonic motion?
 
Bobbywhy said:
I find it difficult to discern periodic motion of that ice floe from the video. There seems to be no fixed reference to use.
You see the bottom of the lake, or rather a wooden coast line wall, that is just under the water line.
Bobbywhy said:
How have the figures “~30 cm range
It might be less in this clip, but it varied. The wooden square pole you see under water is about 7x7cm.
Bobbywhy said:
Assuming that there was a periodic motion as you describe then I think that your proposed cause is plausible: wind-driven oscillation that includes water wave motion.
I wonder if the entire floe is moving like that, or just deforming on the waves.
 
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yup the movement is pretty obvious :)

at the end of the video it showed that the sun was shining.
I wonder what time of the day it was... early ?

I was just thinking that maybe as the sun is rising up over the ice covered lake if there is expansion and contraction occurring in different areas causing the movement ??

Thats assuming a calm windless day. If there was any hint of wind/breeze, then there's another cause of your observed effect :)

Dave

PS ... i love things like this ... Some one notices something that a zillion people may have walked past and not noticed something so subtle as that ... well done on a nice observation :)
 
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