We might never have wondered how a ballpoint pen works. A ballpoint pen is a pen that uses a small roatating ball made of brass, steel or tungsten carbide to disperse ink as we write. Because the tip of a normal ballpoint pen is so tiny, it is hard to imagine that the ball rotates.
It all started with a Hungarian journalist Laszlo Biro who proposed a tiny metal ball that rotated at the end of a tube of quick drying ink. Biro and his brother Georg made the first commercial models, Biro pens. Then in the United States, the first successful, commercially produced ballpoint pen was introduced by Milton Reynolds in 1945.
The main part of the pen is the ball. The width of the ball determines the width of the line drawn by a ballpoint pen. The ball rotates freely and rolls out the ink as it is continuously fed from the ink reservoir (usually a narrow plastic tube filled with ink). The ball is kept in place between the ink reservoir and the paper by a socket. While it is held tight, it still has enough room to roll around as we write. As the pen moves across the paper, the ball turns and gravity forces the ink down the reservoir and onto the ball, where it is transferred onto the paper. It's this rolling mechanism that allows the ink to flow onto the top of the ball and roll onto the paper we are writing on, while at the same time sealing the ink from the air so it does not dry in the reservoir.
The ball and socket unit of a ball point pen is similar to the roll-on we would find in antipersiprants. The roll-on keeps the air out of the liquid antiperspirant while at the same time making it easy to apply.
The ink used in a ballpoint pen is very thick and quick-drying. It is thick so that it doesn't spill out of the reservoir, but thin enough that it responds to gravity. That is why a normal ballpoint pen cannot when we don’t point it towards the ground (imagine writing on a wall), it needs gravity to pull the ink onto the ball.