Propellant

Things push to move.

To go forward, a machine pushes something out the back. This push is called thrust.

Some machines use gas to move. A spray can works this way. It pushes liquid out to make it spray.

Other machines use fuel. They burn fuel to make hot gas. This gas shoots out of a nozzle.

Some rockets use liquid. They use liquids like oxygen and hydrogen. Other rockets use solid parts.

These parts can be shaped like stars. The shape helps them burn. It is how we fly through space.

To move forward, a machine must push something out the back. This push is called thrust. The stuff that gets pushed out is called a propellant.

There are many ways to make thrust. Some machines use fuel. Burning fuel makes hot gas. This gas shoots out of a nozzle to move the vehicle. Chemical rockets often use this way. They might burn hydrogen and oxygen to make steam. The steam is pushed out to provide power.

Other machines use electricity. These spacecraft use electricity to speed up the propellant. They might use an electrostatic force. This force moves tiny bits called ions. Some engines use heat to turn gas into plasma. Plasma is a very hot gas.

Some vehicles use compressed air or water. A water rocket uses compressed air as fuel. The air pushes the water out to make the rocket fly. Most propellants are kept as solids or liquids. This makes them easier to store for a trip.

A propellant is a mass used to create movement. When this mass is pushed out or expanded, it creates a force called thrust. This works because of Newton's third law of motion. This law says that every action has an equal and opposite reaction. To move a vehicle forward, the engine must eject the propellant backward. This process helps move rockets, projectiles, and even fluid payloads.

There are many ways that a propellant works. In chemical rockets, fuel is burned to create a hot, energetic gas. This gas is then pushed through a nozzle to create thrust. The exhaust can be a gas, a liquid, a solid, or even plasma. Some spacecraft use electricity to move their propellant instead. They might use an electrostatic force to push positive ions. Other engines use the Lorentz force to move negative ions and electrons.

Scientists have studied many different kinds of fuel and propellant. In the past, researchers looked at how different substances react together. For example, a simple engine can burn hydrogen and oxygen. This reaction creates H2O, which is water or steam. The energy from this reaction pushes the steam out to provide thrust. Some rockets even use compressed air or water to move. In a water rocket, the compressed air acts as the fuel.

Propellants come in many different forms and mixtures. Most are stored as solids or liquids to save space. Solid propellants are often made in shapes called grains. The shape of a grain changes how fast the fuel burns. Some grains have a star shape in the center to increase surface area. Composites are another type used in large rocket motors. These often use aluminum as a fuel and ammonium perchlorate as an oxidizer.

You can see these ideas in things you use every day. An aerosol can uses a propellant to work. Inside the can, a fluid is compressed to store energy. When you open the valve, the stored energy pushes the fluid out. This force carries the spray out of the can with it. This is very similar to how a rocket uses pressure. Even the light from a star can be thought of as a propellant. Some scientists propose using photons to create thrust in a photon rocket.

A propellant is a mass that is expelled or expanded to create thrust. Thrust is a motive force that moves an object forward. This process follows Newton's third law of motion. This law states that every action has an equal and opposite reaction. To move a vehicle forward, the engine must eject the propellant backward.

This concept applies to many different things. It can move a large rocket or a small projectile. It can even move a fluid payload. In many vehicles, the engine that performs this expulsion is called a reaction engine.

It is important to distinguish between fuel and propellant. Fuel is the substance used to produce energy. Propellant is the reaction mass that is actually pushed out to create movement. In chemical rocket design, people often use the word "propellant" to describe a substance that contains both. However, these are two distinct scientific concepts. The fuel provides the energy, while the propellant provides the mass for the reaction. Even the byproducts of burning fuel can act as a propellant mass. For example, burning hydrogen and oxygen creates H2O, or water. This steam can then be expelled to provide thrust.

There are several ways to power a propellant. Chemical rockets use chemical reactions to create energetic gases. These gases are directed through a nozzle to produce thrust. The resulting exhaust can be a gas, a liquid, a solid, or even a plasma. In aircraft like jets, the propellant is often the product of burning fuel with oxygen from the air. This means the propellant has more mass than the fuel originally carried. Other systems use compressed fluids for movement. A water rocket uses compressed air as fuel to expel water as the propellant.

Spacecraft also use electrical energy to accelerate propellant. One method uses an electrostatic force to expel positive ions. Another method uses the Lorentz force to expel negative ions and electrons. Some engines, called electrothermal engines, use electromagnetic force. These engines heat low molecular weight gases like hydrogen or helium into a plasma. A resistojet engine works differently. It simply uses resistive heating to heat compressed propellant as it is expelled. This increases the thrust produced by the engine.

Solid propellants are often stored in shapes called grains. A grain is any individual particle of fuel or propellant. The size and shape of a grain are very important. They determine the burn time and the rate of energy produced. This affects the thrust profile over time. There are three main types of burns. A progressive burn uses grains with star shapes or perforations to increase surface area. A degressive burn uses simple shapes like cylinders or spheres. A neutral burn uses a single perforation so the surface area stays constant.

Scientists categorize solid propellants into four different compositions. Single-based propellants use nitrocellulose as the main ingredient. Double-based propellants add nitroglycerin to the nitrocellulose to increase energy. Triple-based propellants use nitrocellulose, nitroguanidine, and nitroglycerin, which are often used in cannons. Finally, composite propellants do not use organic nitrates as the primary part. Instead, they use a fuel like aluminum and an oxidizer like ammonium perchlorate. These composites are frequently used in large rocket motors.

Most propellants are stored as solids or liquids to keep them dense. This makes them easier to carry in a vehicle. Some advanced ideas involve using light as a propellant. A proposed photon rocket would use the relativistic momentum of photons. Photons do not have mass, but they move at the speed of light. Because they move so fast, they can still create thrust. To understand this, scientists must use relativistic physics instead of Newton's laws. This shows how the study of propellants connects to the most complex parts of physics.