Jet-propelled describes something that moves forward by shooting a powerful stream of gas or liquid backward. This works because of a basic law of physics: when you push something in one direction, it pushes back with equal force in the opposite direction. Try blowing up a balloon and letting it go without tying it. The air rushes out one way, and the balloon zooms around the room the other way. That's jet propulsion in action.

Jet-propelled airplanes, or jets, burn fuel to create hot gases that blast out the back of their engines at incredible speed. This backward blast drives the plane forward, sometimes faster than the speed of sound. Before jets were invented in the 1930s, airplanes used propellers, which are slower. The first jet-propelled passenger flights in the 1950s revolutionized travel, shrinking a days-long ocean voyage to a few hours in the air.

Nature invented jet propulsion long before humans did. Squids and octopuses are jet-propelled creatures. They suck water into their bodies and then shoot it out forcefully to dart away from predators. When you see a squid suddenly zoom backward in an aquarium, you're watching millions of years of evolution creating the same effect that powers modern aircraft.