Block Sliding Down Ramp With Friction

Instructions
This simulation shows the forces acting on a block as it slides down a ramp. Most parameters are adjustable using sliders. Note that the coefficient of kinetic friction cannot be larger than the coefficient of static friction. If you want a larger value for kinetic, try increasing static.[br][br]Click the play icon in the bottom left corner to animate the block. The acceleration and velocity will update in real time. If the block leaves the bottom of the ramp, it will reappear at the top. The parameters can be adjusted while the animation is playing. Click the reset icon in the top right corner to reset the worksheet to its starting values.
[list=1][*]When is static friction used and when is kinetic friction used?[/*][*]Is [math]f_s[/math] always equal to [math]\mu_sF_N[/math]?[/*][*]What effect does mass have?[/*][*]Can you predict the minimum angle that will cause a block that begins at rest to begin to slide?[/*][*]Once the block begins to slide down the ramp does it accelerate? Always?[/*][*]Can you set the parameters so that the block slides up the ramp before becoming stuck?[/*][*]Setup the block so that it will slide. Calculate the acceleration by hand, and verify that it matches.[/*][/list]

Information: Block Sliding Down Ramp With Friction