Particle

A particle is a separate part of a system.

Some parts are very small. They can be smaller than atoms. Other parts are big. They can be like sand or dust.

Even stars can be seen as particles in a galaxy.

Particles can have mass. This means they have weight. Some parts move very fast. They move at the speed of light. Everything is made of these parts.

A particle is a separate part of a larger system.

They come in many sizes.

Scientists group them into three main sizes. Macroscopic particles are large. These include things like sand, dust, or even stars in a galaxy.

Microscopic particles are much smaller. They include atoms and molecules. The smallest are subatomic particles. These are parts smaller than an atom, like protons and electrons.

Some particles are made of other parts. We call these composite particles. For example, an atom is made of protons, neutrons, and electrons. Other particles are not made of anything else. We call these elementary particles.

Particles also have mass. Mass is how much matter is in an object. Most particles have mass. They must move slower than the speed of light. A few particles have no mass at all. These are called massless particles. They must move at the speed of light.

Some particles are stable. This means they do not break apart. Other particles undergo decay. This means they change into other things.

A particle is a separate part of a larger system.

This is a very general term in science. It can describe many different things. Scientists use it to talk about tiny pieces or huge objects. Anything made of these parts is called particulate. In the air, we often use the word particulate to describe pollution. This usually means tiny bits that are floating around.

These bits might be dust, smoke, or soot.

Particles come in three main size groups. Macroscopic particles are the largest. These include things like sand, powder, or even stars in a galaxy.

Microscopic particles are much smaller. This group includes atoms and molecules. They are studied in chemistry and physics. The smallest group is subatomic particles. These are even smaller than an atom. They include parts like protons, neutrons, and electrons. Scientists study these tiny parts using quantum mechanics.

Scientists also look at what particles are made of. Some are composite particles. This means they are made of other, smaller particles. A carbon-14 atom is a good example. It is made of six protons, eight neutrons, and six electrons. Other particles are called elementary particles. These are not made of anything else. We think things like quarks and gluons are elementary. They do not seem to have any internal structure at all.

Mass is another important way to group particles. A massive particle has more than zero rest mass. Most particles we know are massive. This happens because of the Higgs mechanism. Massive particles must move slower than the speed of light. Some particles are massless, which means they have zero rest mass. Only a few exist, like the photon and the gluon. These massless particles must always move at the speed of light. Even a massive particle can decay into massless ones. For example, a neutral pion can decay into two photons.

Particles help scientists build models of the world. It is hard to track every single tiny movement. Instead, scientists use particles to represent larger things. They might use dots to represent people in a crowd. They might use them to model how galaxies form. In soil, particles are solid and stay in place. They touch each other to pass force along. In liquids, particles can be suspended to form a colloid.

This keeps the tiny parts spread out evenly.

In the physical sciences, a particle is a separate part of a larger system.

The term is very general and changes meaning depending on the field of study. A particle can be a tiny subatomic object or a massive star in a galaxy. Anything composed of these individual parts is described as being particulate. In atmospheric science, the noun particulate often refers to pollutants. These are usually a suspension of unconnected particles floating in the air.

Scientists categorize particles into three distinct size classes. Macroscopic particles are much larger than atoms or molecules. These include sand, dust, or even stars within a galaxy.

Microscopic particles range from the size of atoms to molecules. This group includes nanoparticles and carbon dioxide. Finally, subatomic particles are smaller than atoms. These include protons, neutrons, and electrons. Because they are so small, researchers study them using quantum mechanics. This field explores how they act like both waves and particles.

Particles are also classified by their internal composition. Composite particles are made of other, smaller particles. For example, a carbon-14 atom is a composite particle. It is made of six protons, eight neutrons, and six electrons. In contrast, elementary particles have no internal structure. They are not made of anything else. Scientists believe quarks and gluons are elementary particles.

However, it is possible that some particles we think are elementary are actually composite. We just cannot see their internal structure yet.

Mass is another vital way to distinguish particles in physics. A massive particle has a rest mass greater than zero. Most known particles are massive due to the Higgs mechanism. This mechanism explains why ordinary matter has mass. Massive particles must move at a speed slower than the speed of light. Conversely, a massless particle has zero rest mass. Only a few particles, like the photon and the gluon, are massless. These particles must always move at the speed of light. Mass is not always permanent, as a massive particle can decay into massless ones. A neutral pion, for instance, can decay into two photons in about 10⁻¹⁶ seconds.

Stability is a key characteristic of both elementary and composite particles. Many particles undergo particle decay, which means they change into something else. Particles usually decay from a high-energy state to a lower-energy state. This often happens by emitting radiation, such as photons. Some particles are considered stable because they do not decay. Electrons and helium-4 nuclei are examples of stable particles. Some particles are called observationally stable. This means their lifetime is so long that scientists cannot see them decay.

In many scientific fields, particles are used to create mathematical models. It is often impossible to track every single movement in a complex system. Instead, scientists use particles to represent larger objects. In physics, a baseball might be modeled as a simple sphere. This simplifies calculations for speed and landing location. In cosmology, N-body simulations use particles to model dynamical systems. These simulations can represent stars or galaxies under the influence of gravity. As the number of particles (N) increases, the simulation becomes more computationally intensive.

Particles also play unique roles in Earth and space sciences. In astrophysics, particles appear as cosmic rays or solar wind. Dust particles can aggregate together to form entire planets. In soil science, soil is viewed as a collection of solid particles. These particles transmit force through points of contact. In liquids, particles can form a colloid.

A colloid is a substance where particles are dispersed evenly throughout another substance. These particles can be suspended in a gas to form an aerosol. This concept helps scientists understand everything from air pollution to marine debris.