Why does chalk draw dotted lines when drawn continuously?

[Sho Kano]

What is the physics behind drawing dotted lines with chalk with just one stroke?
This is a video demonstrating this:


Here is what I currently have:

as soon as the applied force exceeds that of the frictional, the block will accelerate. What makes it slip though? Because there is a jerk (change in acceleration) due to the difference between static and kinetic frictional forces?

 

[Andy Resnick]

<snip>What makes it slip though? Because there is a jerk (change in acceleration) due to the difference between static and kinetic frictional forces?

I don't think it's stick-slip behavior, it seems to be more complicated (a "frictional impact oscillator"):

http://www.mate.tue.nl/mate/pdfs/2323.pdf

 

[byteme90k]

can't do that on a dry erase board...just sayin'