A can opener is a device used to open metal

Metal

A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

 cans

Tin can

A tin can, tin , steel can, or a can, is a sealed container for the distribution or storage of goods, composed of thin metal. Many cans require opening by cutting the "end" open; others have removable covers. Cans hold diverse contents: foods, beverages, oil, chemicals, etc."Tin" cans are made...

. Although preservation of food

Canning

Canning is a method of preserving food in which the food contents are processed and sealed in an airtight container. Canning provides a typical shelf life ranging from one to five years, although under specific circumstances a freeze-dried canned product, such as canned, dried lentils, can last as...

 using tin cans had been practiced since at least 1772 in the Netherlands, the first can openers were patented only in 1855 in England and in 1858 in the United States. Those openers were basically variations of a knife, and the 1855 design continues to be produced. The first opener employing the now familiar sharp rotating wheel, which runs around the can's rim cutting the lid, was invented in 1870 but was difficult to operate.