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Author Topic: QotW - 11.08.07 - Why would footprints in sand appear raised?  (Read 21607 times)

Offline CliffordK

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QotW - 11.08.07 - Why would footprints in sand appear raised?
« Reply #25 on: 13/07/2011 17:06:39 »
You may see a little ridging outside of the footprint from the pressure, not in the footprint itself.  However, this is almost purely an optical illusion.

BTW: The link to the podcast is not working yet.
 

Offline TheBeautyHouse

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QotW - 11.08.07 - Why would footprints in sand appear raised?
« Reply #26 on: 14/07/2011 01:37:29 »
I agree with the optical illusion but maybe its just sunken.. I'll try that on the beach..
<may you and your SPAM be lost in sands of time!>
« Last Edit: 14/07/2011 09:49:35 by peppercorn »
 

Offline Airthumbs

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QotW - 11.08.07 - Why would footprints in sand appear raised?
« Reply #27 on: 14/07/2011 07:49:26 »
I was going to say something about the sand possibly behaving elastically but it seems that this is actually an optical delusion.  ::)
 

Offline rhade

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QotW - 11.08.07 - Why would footprints in sand appear raised?
« Reply #28 on: 16/07/2011 01:29:59 »
Uh, I think an optical "delusion" is really called an hallucination.
 

Offline Airthumbs

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QotW - 11.08.07 - Why would footprints in sand appear raised?
« Reply #29 on: 16/07/2011 01:56:43 »
Uh, I think an optical "delusion" is really called an hallucination.

Would that also apply to destruction manuals provided by DIY stores in making cupboards?  ;D

Please excuse my Shakespearean style of English at times, I did live in Warwickshire!

I was on a beech in North Wales under the influence of Magic Mushrooms, when they were legal there, even then the footprints in the sand seemed normal to me....  :P
 

Offline Geezer

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QotW - 11.08.07 - Why would footprints in sand appear raised?
« Reply #30 on: 16/07/2011 05:48:18 »

an hallucination


Yeah! Good on you. I was beginning to think the need for grammar had been abolished (by Rupert Murdoch and his pals at the News of the World, and other publications).

I wonder if he will give all of his money away to charitable organizations to compensate for the damage he has done to other people? Doesn't seem like too much to ask from someone who is obviously interested in the greater good. I suppose we'll just have wait and see. 
 

Offline Airthumbs

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QotW - 11.08.07 - Why would footprints in sand appear raised?
« Reply #31 on: 16/07/2011 17:25:27 »

an hallucination


Yeah! Good on you. I was beginning to think the need for grammar had been abolished (by Rupert Murdoch and his pals at the News of the World, and other publications).

I wonder if he will give all of his money away to charitable organizations to compensate for the damage he has done to other people? Doesn't seem like too much to ask from someone who is obviously interested in the greater good. I suppose we'll just have wait and see. 

Is there a connection with raised footprints here or am I having an hallucination!  ;D  Given the average reading age of the papers Murdoch owns I suspect that his footprints are deeper then most as he is full of excrement!
 

Offline rhade

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QotW - 11.08.07 - Why would footprints in sand appear raised?
« Reply #32 on: 16/07/2011 23:45:49 »
Personally, I blame poor education for falling english standards. I don't know how much we can blame Murdoch for the editorial policy of his papers, also let us not forget he has been propping up the Times at a loss. Not to suggest that he is some kind of philanthropist. I'm sure he's just a businessman, and I won't mourn the loss of one of our seedier tabloids. Sorry if this thread is getting off topic, but I guess it just proves we all care about the world beyond science. I suspect some moderator would jump in if he felt we were breaking some rule.
 

Offline thedoc

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QotW - 11.08.07 - Why would footprints in sand appear raised?
« Reply #33 on: 09/08/2011 17:55:26 »
We put this to Dr Rob Jenkins, a Cognitive Psychologist at the University of Glasgow...

Rob -   The questioner has sent in a wonderful photograph of footprints on a sandy beach.  What's striking about the photograph is that the footprints seems to rise up from the surface of the sand rather than sinking in.  In fact, the footprints are normal footprints.  They're sunk in as you would expect.  Their raised appearance is an illusion caused by the pattern of shadows.  These shadows are ambiguous.  They could result either from bumps lit from the top of the picture plane, or from indentations lit from the bottom of the picture plane.  In the face of this ambiguity, the brain makes its best guess as to which is more likely and that is what we see.  With this particular image, our brains make the wrong call.  Why?  Because they have a built-in bias to assume that light comes from above.  This is a sensible rule of thumb because sunlight generally does come from above, but not in this photograph.  Here, the sun is setting behind the photographer, below the bottom of the picture plane.  This is evident from clumps of sand in the foreground that act as mini sundials.  Under these lighting conditions, only indented footprints could create the pattern of shadows we see.  So the footprints must be indentations after all.

Diana -   So the problem is that our brains have a bias toward top down illumination which means that the brain tends to assume light is coming from above.  This bias is so strong that it often competes and overcomes the clues our vision is giving us about relative depths.  So when light comes from a slightly different angle, in the case of the footprints in low sun, our brain tries to tell us they're convex instead of concave.
                                        Find out more on our podcast page
 ...or Listen to the Answer or [download as MP3]
« Last Edit: 09/08/2011 17:57:49 by BenV »
 

Rklawton

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« Reply #34 on: 11/08/2014 02:06:09 »
I'm the photographer who took the picture featured in Rob's reply. The prints are concave. Perhaps it's because I took the picture, but I've never seen them as anything but concave. ~Rklawton
 

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« Reply #34 on: 11/08/2014 02:06:09 »

 

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