Momentary switches are used in lots of electric tools. The buttons on a pocket calculator, the trigger on a power drill and even your computer's mouse buttons and keys are all momentary switches. These switches are called "momentary" because they usually change a circuit for only a moment, the brief time your finger pushes on it. Some momentary switches, like the power drill trigger or a key on a synthesizer, are most often held down for many seconds. Momentary switches are extremely cheap and common, but you can make your own from a few common items.
Solder a piece of wire to the edge of each penny, one wire per penny.
Tape or glue the pennies to the insides of the legs of the clothespin, one penny per leg. The legs are the parts you squeeze with your fingers to open the clothespin. Make sure that when you squeeze the legs, the pennies touch each other, and that they do not touch otherwise.
Touch the probes of the ohmmeter to the ends of the switch's wires, one wire per probe.
Test your switch by squeezing the clothespin while watching the ohmmeter. The electrical resistance should move from an extremely high value to almost zero when the pennies touch.
Use your new switch in any electrical circuit you wish.
Clean the pennies with brass polish or a salt-vinegar mixture to make sure they will conduct electricity well if they aren't clean and shiny already. Heat each penny well when soldering to ensure a strong electrical bond. Pennies usually require more heat from the iron than other electrical components. Reverse the behaviour of your switch by attaching the pennies to the insides of the jaws of the clothespin instead of the legs. Now, your switch will break a circuit instead of completing it. In electrical terms, you've changed your switch from a push-to-make to a push-to-break switch.
Make sure to let the pennies cool after soldering before touching them.