Jet propulsion

Jet propulsion is a way to move something by shooting out a stream of fluid, like air or water, in the opposite direction. This works because of a basic rule of physics: when something pushes on another thing, that other thing pushes back with an equal force. This idea is called Newton's third law.

Many machines use jet propulsion. Jet engines power airplanes, helping them fly. In the water, pump-jets help boats and ships move quickly. Rockets and special space engines called plasma thrusters also use jet propulsion to travel through space.

Some sea animals use jet propulsion to move. Octopuses and salps, which are tiny sea creatures, can squirt water out of their bodies to zoom away quickly. The flying squid can use jet propulsion underwater and also in the air when it jumps out of the water.

Physics

Jet propulsion happens when something moves forward by shooting out a fast stream of fluid in the opposite direction. This works because of Newton's laws of motion, which tell us that every action has an equal and opposite reaction.

Some animals also use jet propulsion to move quickly, especially when they are large and moving through water or air.

Specific impulse measures how well a jet engine or rocket uses its fuel. A higher specific impulse means the engine uses fuel more efficiently. Thrust is the force that pushes the engine forward.

Types of reaction engine

Main article: Reaction engine

Reaction engines move by pushing out solid or liquid material. Jet propulsion means engines that use liquid material for this.

Jet engine

Main article: Jet engine

A jet engine is a type of reaction engine that uses air around it. It heats the air and pushes it out to move. Most jet engines work like gas turbines using the Brayton Cycle. There are many kinds, such as turbojets and turbofans. Others, like ramjets and pulse jets, work best when moving very fast.

Rocket engine

Main article: Rocket engine

Rocket engines can work in space because they carry their own air or use special reactors to heat materials.

Plasma engine

Main article: Plasma propulsion engine

Plasma engines push out a special material called plasma using electric forces.

Pump-jet

Main article: Pump-jet

Pump-jets help boats move. They use water pressed by special propellers or pumps to create movement.

Jet-propelled animals

Main article: Aquatic locomotion § Jet propulsion

Some animals use jet propulsion to move quickly. Squids push water out of a tube to zoom away from danger. This water passes through their gills, helping them breathe and move at the same time.

Other sea creatures like sea hares and some small fish also use jet propulsion. Even tiny dragonfly babies and some jellyfish push water out to move. These methods help them travel efficiently through the water.