Tetris is a game about falling blocks. They fall at a constant velocity, or at a much faster rate. Realistically, gravity would cause the blocks to accelerate. Two options exist for Tetris to realistically exist, assuming the board is set up vertically. One, the game is set in space, and each block has a constant force acting towards the ground, or two, a force is acting against gravity such that there is no acceleration on the block. However, each round the blocks fall at a faster velocity, therefore we can determine that the force acting on the tetris pieces is changing.