NTNUJAVA Virtual Physics Laboratory
Enjoy the fun of physics with simulations!
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Author Topic: The world above the water surface, as seen by a fish  (Read 157384 times)
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Fu-Kwun Hwang
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on: January 29, 2004, 10:33:34 pm » posted from:,,Satellite Provider

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When light propagates from one medium into another, its speed changes,
which causes the light to reflect and refract at the boundary.
 The index of refraction of water is 1.33 (4/3).
As light travels from water to air, it will bend away from the perpendicular to the surface.
When the incident angle is greater than 48 degrees, all the light is reflected back into the water (total internal reflection).

 As your pet goldfish in the aquarium looks up, it will see a reflected view of the sides and bottom of the aquarium beyond the 48 degree angle, while directly above, it sees a compressed view of the outside world.
 The refraction of light is responsible for many illusions:
  • The shape of a thing you see under the water surface is different from what it really is.

  • A submerged object appears to be nearer the surface than it actually is.

This java applet lets you see the view as seen by your fish, looking up at you.. Pretty weird!

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 Usage: The area is divided into two regions.
The light gray area is the air above the water surface. The green area is below the water surface.
A fish with two eyes is under the water surface.
 All the light from the world above the water surface that the fish can see enters the water through yellow region.
 The cyan colored block is an object above the water surface. The blue polygon is the imageof the block.
 The light path for each corner of the object is shown by the light gray lines.
 The yellow lines indicate where the object appears to be, to the fish.
As you will discover, the fish sees the world in very distorted form.

 Click one of the corners of the cyan block with the left mouse button to view light paths for that point.
 Click near the center of the block with the left mouse button and drag the mouse to move the object.
 Click the right bottom corner of the block with right mouse button and drag the mouse to change the size of the object.
 Move the object from LEFT TO RIGHT / UP AND DOWN/CHANGE ITS SIZE, and watch how the image changes.
Click at one of fish's eyes and drag the mouse button (left/right) to change the location of the eye.
 It's fun! Play with it! Think about it! Fish have to understand this! Enjoy the fun of physics. : ) Fill a glass with water and look at objects beneath the surface. Try it!





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*** There are 1 more attached files. You need to login to acces it!
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AlbertF
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Reply #1 on: October 06, 2009, 12:43:34 pm » posted from:Berkeley,California,United States

This is a quite an old and quirky Javascript program back from 2004.
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Fu-Kwun Hwang
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Reply #2 on: October 06, 2009, 02:54:58 pm » posted from:Taipei,T'ai-pei,Taiwan

It is a java simulation. There is no javascript used in the above applet.
Java and Javascript are not the same (or similar at all).
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Bennigno
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Reply #3 on: February 11, 2010, 12:58:51 pm » posted from:Mountain View,California,United States

Hi Prof Hwang,
  could you share the jar or xml source file of this java applet? I'd like to change the index of the water so that i can show the illusion position of what fish thinks. Or you could also add a negative checkbox into the current applet.
Many thanks!
CW
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Reply #4 on: February 11, 2010, 01:23:13 pm » posted from:SINGAPORE,SINGAPORE,SINGAPORE

this is a older JDK1.0.2 simulations, they are not made using Easy Java Simulation (Ejs), thus they do not have *.xml source codes.

But you can download the standalone files, it think the source is inside but cannot be read by Ejs.

hope that helps Grin
by the way,
you can search the entire forum and find that Prof Hwang has an Ejs version of a similar applet
An object under the water look differ! (Location and shape)
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=378.0
« Last Edit: February 11, 2010, 01:25:14 pm by lookang » Logged
Fu-Kwun Hwang
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Reply #5 on: February 11, 2010, 02:32:36 pm » posted from:Taipei,T\'ai-pei,Taiwan

The above applet was created with JDK 1.0.2
The java source code is available (attached file) if you want to modify it by yourself.
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leeyiren
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Reply #6 on: March 25, 2010, 12:08:59 am »

In the fish eye view from the water, why the image appears distorted? Any simple clear concise explanation? Thanks.
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Reply #7 on: March 25, 2010, 02:14:13 pm » posted from:Singapore,,Singapore

this is the same concept but the direction of light is opposite.

simply put, it is refraction of light Smiley hope it helps
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Fu-Kwun Hwang
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Reply #8 on: March 25, 2010, 09:24:52 pm » posted from:Taipei,T\'ai-pei,Taiwan

In the fish eye view from the water, why the image appears distorted? Any simple clear concise explanation? Thanks.

The first simulation was designed to help you understand why the image appears distored.
Please try to click the four corner of the object, the bending of the ray is different at different position.
The image was calculated from all points at the object. two rays emmitted from the the same point will refracted at different angle.  the interaction point of those two yellow line is the place where fish will see the image from that point.

You are welcomed to check out the following related applets.
An object under the water look differ! (Location and shape)
Where is the fish? (Refraction)
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koclup1580
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Reply #9 on: November 15, 2012, 12:31:09 pm » posted from:Bangkok,Krung Thep,Thailand

thank you.. Smiley
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gulinekxchr
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Reply #10 on: March 21, 2013, 01:08:18 pm » posted from:Tokyo,Tokyo,Japan

Some of their own ideas, I do first under my experiment
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GolfBallJuggler
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Reply #11 on: April 21, 2013, 09:13:29 am » posted from:Singapore,,Singapore

How do I run this program offline...
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Fu-Kwun Hwang
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Reply #12 on: April 21, 2013, 01:11:49 pm » posted from:,,Satellite Provider

Did you find "get file for offline use button"?

Download file, unzip it and open index.html with your browser.
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tosraj
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Reply #13 on: May 13, 2013, 07:40:49 pm » posted from:Bangalore,Karnataka,India

I don't understand as to why light enters the water only through the yellow region. I understand that beyond the yellow region, the reflected bottom of the pool will be seen (green rays in figure below), but wouldn't it be a dim (less bright) compared to the light entering the water from the air (red rays in figure below) and reaching the fish? I assume a infinite or very large pond here (not an aquarium where light may enter from the sides too) so that the reflected light from the bottom of the pond is quite dim. Hence the fish must see the outside world superimposed with a dim reflection of the bottom of the pond. Where am I going wrong?

Thanks in advance for your reply and for your great post.

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There is a better way to do it; find it. ..."Thomas Edison(1847-1931, American inventor, 1093 patients)"
 
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