Potassium is a soft, silvery metal and one of the essential chemical elements. Your body needs potassium to function properly: it helps your muscles contract, your heart beat steadily, and your nerves send signals throughout your body. Without enough potassium, you'd feel weak and tired, and your heart wouldn't work correctly.

You get potassium from foods like bananas, potatoes, spinach, and beans. When someone talks about eating a banana for energy before a sports game, they're partly talking about the potassium it contains. The element appears on the periodic table with the symbol K, which comes from its Latin name, kalium.

Potassium is also used outside the body in important ways. Farmers add potassium fertilizers to soil to help crops grow strong and healthy. The element is so reactive that pure potassium metal can burst into flames if it touches water, which is why scientists store it in oil. This extreme reactivity makes potassium fascinating to chemists but also means you'll never encounter pure potassium metal in everyday life: you'll only see it safely combined with other elements in compounds like potassium chloride in table salt substitutes or potassium nitrate used in fireworks.