Algodoo

Create a box almost equal to the size of the grey on top of the "sharpener"
Play
Look it go!
NOT FOR SLOW COMPUTERS NOT FOR SLOW COMPUTERS NOT FOR SLOW COMPUTERS
NOT FOR SLOW COMPUTERS NOT FOR SLOW COMPUTERS NOT FOR SLOW COMPUTERS
Your game will lag during the sharpening, but its worth it cause its awesome

Also if you didnt get it, there is a demonstration