The tiny rotating ball inside a ballpoint pen
A ballpoint pen writes with a tiny ball held in a socket at its tip. As the ball rolls across paper, it picks up ink from inside and transfers it onto the surface. The close-fitting socket controls the ink around the ball, allowing a thin trail instead of an open stream from the reservoir.
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A rolling ink transfer system
The visible point of a ballpoint pen contains a small, hard ball. A socket holds it securely while allowing it to rotate.
Ink reaches the inner side of that ball from the reservoir. Contact with the paper turns the ball, carrying ink around to the outside and leaving a line behind. The narrow spaces around the ball help control the flow.
The tip is a moving part, even though its motion is too small to notice easily. It acts more like a miniature roller than a brush.
- The reservoir stores the ink.
- The socket holds and guides the ball.
- The rotating ball transfers ink to the paper.
Ordinary ballpoint ink is relatively thick. Ink supply, the condition of the tip and the surface being written on all affect whether the line appears smoothly or skips.