In a clock the power from the weight or mainspring is delivered through the train of gears to the escapement.
The escapement gives a small impulse to the pendulum to keep it going. With each swing of the pendulum one tooth of the escape wheel is released and thus the gears turn in tiny steps, at a rate controlled by the swing of the pendulum. The gear ratio is chosen so the hands of the clock turn at the correct rate. If a clock has a very short pendulum, the escape wheel teeth will be released at a faster rate, and so the gear ratio between the escapement and the hands will be different.