All forces acting on the block are shown. These include the gravitational force, friction force, and Normal force due to the inclined plane.
Unlike a picture in a book, this picture can be modified by the student. The angle of the inclined plane can be changed by dragging the handle at the top corner of the inclined plane up or down with a mouse. The friction coefficient may be altered by moving the slider on the right up and down. As these change, the arrows representing the forces change in magnitude and, if the plane angle is changed, in direction. If the plane becomes steep enough or the friction coefficient small enough, the total force on the block may not be zero, and the block will accelerate down the plane.
Unfortunately it is not presently possible to use the keyboard to control things like the friction slider or plane angle handle in VRML. Therefore it is tricky but nonetheless possible for a blind student to access the friction and plane angle controls. The student needs a tactile copy on a digitizing pad and can locate either the friction slider or the plane handle, lock the mouse to it, and move it up or down in the figure. Screen readers have mouse lock keys, so this operation is straightforward.
A button in the lower right corner permits the user to turn sounds and labels off and on. Default is "on". When the mouse pointer is moved, a click is heard as it enters and leaves an object. Object labels are displayed in a lower frame and will normally be spoken automatically by a screen reader.This is the same technique used for the bit-map accessibility discussed previously. Netscape 4 or Internet Explorer 4 are required here.
If the user reduces the friction coefficient or increases the plane angle sufficiently to make the block slide, one hears a sliding sound and the block thump at the end of the plane. With patience, a blind user can use the combination of audio and the tactile figure to achieve fairly good access. Clearly a haptic mouse would improve access to this type of figure however.
Readers may download a VRML browser CosmoPlayer2.1 from CosmoSoftware or WorldView2.1 from Intervista to view the example interactively.VRML sliding block example (VRML browser required!)
For the benefit of sighted readers who don't want to take time to load
a VRML browser, the
sliding
block example screen picture is shown here.
The user can automatically generate a black and white outline image of the sliding block example for making a tactile print.
The above outline picture can also be scaled for any size digitizing pad and printed on swell paper or on the TIGER. The TIGER embossed image is shown below.
TIGER outline image of sliding block example
This example demonstrates a universal VRML widget for displaying x-y graphs. As an illustration we have taken the graph of the electric potential of several electric charges located at various points along the x axis. The size of the interval and the location and both size and magnitude of the electric charges can be chosen by the user. The value of the potential is displayed at any point as the mouse cursor is moved along the x direction. We have chosen to display these values in the status line so that the last two examples can be viewed without the latest version internet browsers. These status lines can also be read by a screen reader.
In addition, the graph may be played as a tone graph by clicking the mouse. A tone graph will be played for data beginning at the x value of the pointer.
Screen picture of X-Y graph with initial charge distribution.
Screen picture of X-Y graph with modified charge distribution.
VRML example of x-y graph. (VRML browser required!)This example illustrates a universal VRML widget for 2D function plots. These are widely used to show functions of two variables. Familiar examples are topological maps and temperature regions on a weather map.
This example shows the electric potential due to charges in a plane. The position of the charges may be changed by the user by dragging with a mouse. Positive potentials are shown in red. Negative potentials are shown in blue.
The value of the potential at any point is shown in the status line. In addition, a user may hear a tone graph by clicking and dragging the mouse along an arbitrary path. A blind reader will undoubtedly wish to use a touch pad instead of a mouse.
Screen picture of potential for initial charge distribution, a black and white outline picture of potential and ready to print (for tactile copy) scaled outline picture of potential.
Screen picture of potential for modified charge distribution.
VRML example of 2D potential Plot. (VRML browser required!)
