Ballpoint pens have a tiny ball made of brass, steel or tungsten carbide as their writing tip. The ball is fitted into a socket and is connected to the ink reservoir by a thin tube. When we write on paper, the ball rolls due to friction between the ball and the paper. This rotating movement allows the thick ink to flow out slowly leaving a mark on the paper.
When drawn over a smooth surface such as glass or plastic there is little friction between the ball and the surface. The ball is unable to rotate and, as a result, the ink cannot flow out. Hence we cannot write on smooth surfaces with a ballpoint pen.