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This applet is a simulation that demonstrates scalar waves in two dimensions. Wave motion crops up in many different areas in physics; water waves, sound, and light are three examples.

When the applet starts up you will see a white square (called the "source") emitting circular waves. The light areas are positive and the dark areas are negative. So, if you prefer to think of the waves as sound waves, the light areas would be areas of high pressure, and the dark areas would be low pressure. The source might be a speaker of some sort.

You can drag the source around wherever you want. Also you can create new waves (areas of high pressure) by clicking anywhere. There is a popup menu that controls what the mouse does. By default it is set to "Mouse = Draw Wave (+)". Hold down the command or alt key while drawing to freeze the simulation.

Click the right mouse to bring up a popup menu to add various objects to block the path of the waves. Once you select one, it will be placed on the screen, and you can draw it anywhere you like, or click and drag the ends of it to resize it. Right-click on the object to edit its parameters.

The Setup popup can be used to view some interesting pre-defined experiments. Once an experiment is selected, you may modify it all you want. The choices are:

If the Mouse popup is set to Mouse = Hold Wave (+), then if you click on a point and hold the mouse down, it will create a positive area on the screen which will persist as long as the mouse is down. This will cause the surrounding area to also be positive. For sound waves, this is like adding air at that point; it puts more pressure on the surrounding area.

The Clear Waves button clears out any waves but does not remove any walls or sources.

The Stopped checkbox stops the applet, in case you want to take a closer look at something, or if you want to work on something with the mouse without worrying about it changing out from under you.

The Waves popup determines what type of waves are being simulated. The type of waves affects two things: the screen width scale, and the response when a wave hits a wall. For acoustic waves, waves will be reflected with no phase change (so, positive wavefronts will still be positive when reflected). Otherwise, waves will be reflected negatively (positive wavefronts will be negative when reflected).

The screen width scale depends on the setting of the Waves popup, but you can also set it manually by going to File->Options. Setting the width of the screen in meters doesn't affect the simulation but it does affect the coordinate display, and the values that are displayed for object parameters (lengths, widths, wavelengths, etc).

The 3-D View checkbox gives you a 3-D view. You can rotate the view by dragging the mouse, but you can't modify the waves or walls in this mode. The brightness slider will adjust the height of the waves.

The Simulation Speed slider controls how far the waves move between frames. If you slide this to the left, the applet will go faster but the motion will be choppier.

The Resolution slider allows you to speed up or slow down the applet by adjusting the resolution; a higher resolution is slower but looks better.

The Brightness slider controls the brightness, just like on a TV set. This can be used to view faint waves more easily.

Click here to go to the applet.