Elementary particle facts for kids
Imagine tiny building blocks that can't be broken down into anything smaller. In science, we call these elementary particles or fundamental particles. They are the most basic pieces of matter and energy in the universe.
These particles come in two main types: fermions and bosons. Fermions are like the ingredients that make up everything around us, and they have mass. Bosons are like the messengers that carry forces between fermions, and some of them don't have any mass. The Standard Model is a big theory that helps scientists understand how these particles work and the forces that act on them. According to this model, elementary particles are grouped into quarks, leptons, and bosons.
Of the particles that make up an atom, only the electron is an elementary particle. Protons and neutrons are actually made of three smaller particles called quarks. This means protons and neutrons are not elementary; they are "composite" particles. The quarks inside protons and neutrons are held together by other elementary particles called gluons.
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What Makes Particles Unique?
Every elementary particle has three basic properties that help us describe it: mass, charge, and spin. Each property has a specific number value. Sometimes, this value can be zero. For example, a photon has no mass, and a neutrino has no electric charge. These properties always stay the same for an elementary particle.
Mass
A particle has mass if it takes energy to make it speed up or change direction. The mass of elementary particles is often measured in units like "MeV/c2" (pronounced "megaelectronvolts over c squared"). This unit comes from special relativity, which teaches us that energy and mass are related. All particles with mass create gravity. All particles are affected by gravity, even those with no mass, like the photon.
Electric Charge
Particles can have a positive charge, a negative charge, or no charge at all.
- If a particle has a negative charge and another has a positive charge, they pull towards each other.
- If two particles both have negative charges, or both have positive charges, they push away from each other.
This electric force is much stronger than gravity at short distances. An electron has a charge of -1. A proton has a charge of +1. A neutron has an average charge of 0. Quarks have charges like ⅔ or -⅓.
Spin
Particles have a property called "spin number." This isn't like a spinning top, but it's a way to describe their internal angular momentum. For elementary particles, the spin number is either 1 or ½. This property affects how particles behave in the tiny world of subatomic particles.
Mass and charge are properties we see in everyday life because gravity and electricity affect things we can touch. But spin mostly affects the world of tiny particles, so we can't observe it directly.
Fermions: The Building Blocks
Fermions are named after scientist Enrico Fermi. They have a spin number of ½. Fermions are either quarks or leptons. There are 12 different types of fermions, not counting their antimatter partners. Each type is called a "flavor."
Quarks
There are six flavors of quarks:
- up
- down
- charm
- strange
- top
- bottom
Quarks come in three pairs, called "generations." The first generation (up and down) is the lightest. The third generation (top and bottom) is the heaviest. One quark in each pair (up, charm, and top) has a charge of ⅔. The other quark (down, strange, and bottom) has a charge of -⅓.
Leptons
There are also six flavors of leptons:
- electron
- muon
- tau
- electron neutrino
- muon neutrino
- tau neutrino
The neutrinos have no electric charge. The other leptons (electron, muon, tau) have a charge of -1. Each neutrino is named after its corresponding charged lepton.
Six of the 12 fermions are thought to last forever: up and down quarks, the electron, and the three kinds of neutrinos. The other fermions decay, meaning they break down into other particles very quickly after they are made.
Bosons: The Force Carriers
Bosons, named after physicist Satyendra Nath Bose, have a spin of 1. Most bosons are made of more than one particle, but there are two kinds of elementary bosons: gauge bosons and the Higgs boson.
Gauge Bosons
These bosons carry three of the four fundamental forces. They include:
- Gluons: These are massless and chargeless particles. They carry the strong force, which is the strongest force. Gluons, along with quarks, join together to make composite particles like protons and neutrons.
- W and Z bosons: These particles carry the weak force. The W boson has a positive particle (W+) and a negative particle (W-). The Z boson is its own anti-particle. W and Z bosons were discovered in 1983.
- Photons: These are massless and chargeless particles that carry the electromagnetic force. Photons are light particles. They travel at the speed of light (about 300,000 kilometers per second).
Higgs Boson
Physicists believe that particles have mass because of something called the Higgs field. The Higgs boson is the particle associated with this field. It helps explain why some particles have mass and others, like photons, do not.
The photon and the gluons have no charge and are the only elementary particles that have a mass of 0 for sure. The photon is the only boson that does not decay. Unlike fermions, it is possible for many bosons to be in the same space at the same time.
The Standard Model includes all the elementary particles described above. All these particles have been observed in laboratories. The Standard Model does not include gravity. If gravity works like the other three fundamental forces, then it might be carried by a hypothetical boson called the graviton. However, the graviton has not yet been found.
The first fermion discovered was the electron. The first boson discovered was the photon. The theory that best explains how the electron, photon, and electromagnetism work together is called quantum electrodynamics.
See also
In Spanish: Partícula elemental para niños
