A block slides down an inclined plane. Both the angle at which the ramp is inclined and the length of the ramp are displayed in the upper-right hand corner. You can change the angle or the length by using the mouse to drag the bottom of the ramp. You can also use the Scale menu to modify the scale with which the ramp is measured. If you pull down the Slide menu and select the Start option, the block will begin sliding down the ramp. As it slides, the distance that the block has moved is displayed in the lower-right corner, and the time that has passed is displayed at the top. Set the ramp so that it is at 45 degrees. The coefficient of friction is displayed in the lower-right corner. Initially, it is zero, which means that there is no friction. Use the controls to set the coefficient of friction to 1.0, and start the simulation. Time will begin ticking, but the block will not move. When the coefficient of friction is 1.0, no motion occurs on a 45 degree ramp. If you reduce the friction slightly, the block should begin moving, more slowly than it did in the absence of friction. Some example coefficients of friction are 0.01 for skis on snow, 0.1 for brass on glass, and 0.5 for rubbing your hands together. Now pull down the Slide menu and select the Two Ramps option. The simulation window will double in size, and a second ramp (complete with its own controls) will appear. Although the two ramps will initially be identical, you can configure them individually and arrange "races" between the blocks.