How is it a ballpoint pen which did not work previously, miraculously starts working again when you make a few scratches with it on paper? What’s the mechanism behind it?
In: Engineering
Ballpoint pens have a steel ball sealing the ink in the pen. The ink is too thick to flow around the ball. However when you drag the ball over a surface it will spin and drag some of the ink with it therefore metering the ink onto the surface. However if you leave the pen unused for a while the ink around the steel ball can dry up locking the ball from rotating. You need to write on a surface with some friction in order to free the steel ball from the dried up ink to allow it to rotate again.
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