Liquid hydrogen

Liquid hydrogen is a type of fuel. It's made of two very light elements, hydrogen and oxygen. When these two elements are combined, they form a very cold, liquid gas. Liquid hydrogen is very cold because hydrogen and oxygen freeze when they react with each other. Liquid hydrogen is sometimes used in rockets and other vehicles because it is so powerful. When it's burned, it gives off a lot of energy and is able to propel a rocket or other vehicle very quickly. Liquid hydrogen is also sometimes used to power a type of engine called a fuel cell engine. This engine turns chemical energy to electrical energy, which is then used to power a vehicle.