### Author Topic: An object under the water look differ! (Location and shape)  (Read 81857 times)

#### Fu-Kwun Hwang

• Hero Member
• Posts: 3062
##### An object under the water look differ! (Location and shape)
« on: July 10, 2006, 05:01:09 pm »
When you look at something under the water, not only the position of the object is not located at the place you though it was. The shape of the object is also changed.
Location of the image and its shape are all depend on the location you view it.
This simulation will let you play with it.

You can drag the blue object, change the shape of object and the position of eye with your mouse. The color of the image is cyan.

You can also drag the eye under the water, then you can experience the view under the world.
Because the shape of the image change a lot when viewing at different locations under water.

You will also find another green object under water. And sometime. another image of green object appear above the water. This is due to total reflection. I hope you have fun with this applet. I believe you have never see any simulation like this one.
-*-

: image from http://www.aapt.org/Programs/contests/winners.cfm?theyear=2010
2010 High School Photo Winners 2nd Place
"Light on Water",Erika Lynn Laman, West Boca Raton Community High School Teacher: Mrs. Aparicio

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• Please feel free to post your ideas about how to use the simulation for better teaching and learning.
• Post questions to be asked to help students to think, to explore.
• Upload worksheets as attached files to share with more users.
Let's work together. We can help more users understand physics conceptually and enjoy the fun of learning physics!

#### Fu-Kwun Hwang

• Hero Member
• Posts: 3062
##### topic378
« Reply #1 on: July 10, 2006, 05:07:05 pm »
Another similar version Where is the fish? (Refraction)

Why does a fish appear to be closer to the surface of water than it really is?

The following java applet let you find out the answer,
and learn the physics of refraction, and total internal reflection.

Usage:

A scanning eye represent the observer. You can click on it and drag it to any position you like.
The whole screen will be clear when you drag the scanning eye.

You can draw any pattern you like, and the java program will draw the virtual image of it.
( If the virtual can be formed due to refraction or total internal
reflection)

When you draw in the water region,
the region where the total internal reflection
is possible, will be shown.

If you click the right mouse button, it will show you many light rays emitted.
(including refraction rays and total internal reflection rays)

Right click the mouse button twice is another way to clear the screen.

#### Fu-Kwun Hwang

• Hero Member
• Posts: 3062
##### Re: An object under the water look differ! (Location and shape)
« Reply #2 on: February 22, 2007, 04:32:27 pm »
Email message received from one of the user:

Quote
I teach 16-19 year youth in technology and physics.
I have had serious problems this week explaining to them the physics behind "the fishermans problem": How to catch a fish with a spear in shallow waters.

I tried your java applet 1 and 2 - mostly no 2 with the user playing with the eye placement.

I try to imagine the fisherman pointing at the fish with a spear.
A suggestion could be to equip the fisherman with a spear pointing to the water. The spear could be represented by a straight line from one of the eyes - "the pointing eye" -the fisherman closes his other eye and points at the image of the fish.

My students got very frustrated when they discovered that a laser light beam is bent according to the law of refraction while the image of a spear will bend the opposite way.

I am now looking for an explanation for them !?

Thanks for the time you have spent at your homepage!

When we are stand in front of a mirror, we saw our image inside(behind) the mirror.
Because lights emitted from our body were reflected back at the mirror surface and enter out eye.
Our mind can trace those light paths which enter our eye and interpret that image was form inside(behind) the mirror.
However, we all know that it is the image (not the real object) which is inside (behind) the mirror.
The same effect occurs for the fishman problem:

From the above simulation,  red lines are the light paths for light emitted from the object, due to refraction, those two lines are bent at the water surface, and enter eye to have visual effect.

Our mind trace back with the orange lines to find the location of the image.
And fishman will interpret the image as the real object.

I would suggest you find a transparent water tank, put some object inside.
Ask a student to point a long stick from eye position to the image of the object.
Also use a laser pointer  pointing from eye along the stick to the water surface,
the llight from the laser pointer will hit the real object (light will be bent due to refraction at the water surface).

#### VIV0411

• Newbie
• Posts: 1
##### Re: An object under the water look differ! (Location and shape)
« Reply #3 on: May 01, 2010, 07:53:13 pm »
Hats off to your creativity sir.

#### Fu-Kwun Hwang

• Hero Member
• Posts: 3062
##### Re: An object under the water look differ! (Location and shape)
« Reply #4 on: September 13, 2010, 01:47:50 pm »
When you drag the eye under water you will find some strange image like the following:
Do you know why therr is an extra image?

Hints:  Under water, the water surface is behavior like a mirror
Check out the following Youtube movie and watch the image form by (light reflect from) water surface.

#### Fu-Kwun Hwang

• Hero Member
• Posts: 3062
##### Re: An object under the water look differ! (Location and shape)
« Reply #5 on: January 10, 2012, 09:59:08 pm »
Here is another related youtube movie

#### Fu-Kwun Hwang

• Hero Member
• Posts: 3062
##### Re: An object under the water look differ! (Location and shape)
« Reply #6 on: December 10, 2013, 09:12:59 am »
Here is another version: Watching object in a rectangle transparent water tank.

The gray area is where total internal reflection occurs.

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