spring moves downward. (Actually, the force is proportional to the sine of the angle, which is approximately proportional to the angle for small angles.) As the actuator depresses it flexes the flat spring while the curved spring keeps the electrical contacts touching. When the flat spring is flexed enough it will provide sufficient force to compress the curved spring and the contacts will begin to move. As the flat spring moves downward the upward force of the curved spring reduces causing the motion to accelerate even in the absence of further movement of the actuator until the flat spring impacts the normally-open contact. Even though the flat spring unflexes as it moves downward, the switch is designed so the net effect is acceleration. This "over-center" action produces a very distinctive clicking sound and a very crisp feel. In the actuated position the curved spring provides some upward force. If the actuator is released this will move the flat spring upward. As the flat spring moves, the force from the curved spring increases. This results in acceleration until the normally-closed contacts are hit. Just as in the downward direction, the switch is designed so that the curved spring is strong enough to move the contacts, even if the flat spring must flex, because the actuator does not move during the changeover. Applications Microswitches have two main areas of application: Firstly they are used when a low operating force with a clearly defined action is needed. Secondly they are used when long-term reliability is needed. This is a result of the internal mechanism and the independence of the closing force on the switch contacts from the operating force. Switch reliability is largely a question of the contact force: a force that is reliably adequate, but never excessive, encourages long life. Common applications of micro switches include the door interlock on a microwave oven, leveling and safety switches in elevators, vending machines, arcade buttons, and to detect paper jams or other faults in photocopiers. Microswitches are commonly used in tamper switches on gate valves on fire sprinkler systems and other water pipe systems, where it is necessary to know if a valve has been opened or shut. Microswitches are very widely used; among their applications are appliances, machinery, industrial controls, vehicles, convertible tops, and many other places for control of electrical circuits. They are usually rated to carry current in control circuits only,