The battery alone could not have caused the weight to move much, because batteries discharge slowly and gradually. Capacitors, on the other hand, discharge quickly, providing stronger current over a shorter period of time.
Inside the capacitor, the positive and negative terminals connect to two metal plates separated by an insulating substance referred to as the dielectric. The dielectric is made from a material that is highly resistant to electric current, such as ceramic or glass, that keeps the plates from touching each other and allows them to hold opposite charges. Those opposite charges allow the capacitor to maintain an electric field across the gap between the plates.
When the knife switch closes the circuit to connect the motor, the electrons on the capacitor’s negative side are drawn through the circuit to the capacitor’s positive side. They rush along the now available path straight through the motor. The electricity powers the motor to lift the weight until the capacitor charge dissipates. The surge of electrical energy that the capacitor provides makes it perfect for applications like flash bulbs and the starter in your car.