Cell division is an integral part of the cell cycle where genetic material must be spatially partitioned precisely. Bacterial cells utilizes a division ring, call the Z-ring, to "pinch" the cell into two equal halves. The Z-ring has been postulated as a mechanical force generator. By considering the problem physically, and taking into account the growth mechanism of the cell wall, we quantify and predict the magnitude of the force generated by the Z-ring. A dynamic model of the cell wall is proposed. The predicted force also points to a new mechanism of force generation without molecular motors.