| Flavour | Charge | | up | +2/3 | | down | -1/3 |
| | Table1 |
| | Quarks are fundamental. They make up one family of fundamental particles. The other family is the leptons (the electron's family). Although the quarks are a family of fundamental particles, they never exist on their own. They are only ever found as combinations in protons, neutrons and the other hadrons. | | Mixing flavours |
| 
M1e |
| Protons and neutrons are made of two types of quark. These quarks are said to have different flavours: up and down. These up and down quarks are the only quarks that are found in normal matter and they are known as first generation quarks. |
|
M2e |
| Nucleon | Quarks | Representation | | proton | up
up
down |  | | neutron | up
down
down |  |
| | Table 2 |
| | A proton is made from two up quarks and a down quark. A neutron is made from two down quarks and an up quark. Table 1 shows the properties of these quarks and how they combine to give the charges of protons and neutrons. You can read more about quarks in the extension page. |
| |
| Picturing properties
We can never see these tiny particles because they are smaller than the wavelength of visible light but we can look into their properties. For example, we can work out their charge and measure their mass. Charge and mass are familiar properties because we can also measure the charge and mass of everyday objects. However, sub-atomic particles have other properties that do not appear in everyday objects. One of these is the flavour of a quark. This is nothing like the flavour of something we eat (like ice cream) but it is a word that means something particular to physicists, who know when they use it exactly what they are talking about. (There are some much crazier names that you will come across.) |
| |
| | Holding the nucleus together |
| |
The forces between protons. | | | Force | Has effect on | | Gravity | Anything with mass | | Electromagnetic | Anything with charge | | Strong nuclear | Quarks but not leptons |
| | Table 3. The strong nuclear force is a new force needed to explain why protons and neutrons bind in the nucleus. |
|
| | The nucleus of helium contains two protons. They are both positively charged and will repel each other. However, they stay bound in a helium nucleus. Therefore there must be another force that holds them together. This is the strong nuclear force, which is the third force in our model (Table 3). It is an attractive force that only has an effect over a very short range (about 10-15 metres - the size of the nucleus). The strong nuclear force binds protons and neutrons together to make the nucleus. The strong nuclear force is actually a force between quarks and is carried by particles called gluons. Protons and neutrons are made of quarks and they feel the strong nuclear force as well. |
|
M5e |
| Familiar feelings | | Electrons do not feel the strong nuclear force. Fundamental particles that don't feel the strong nuclear force are all in the family of leptons. Particles in the quark family do feel the strong nuclear force. So do the hadrons like protons and neutrons, which are made up of quarks.
|
| |
| | | |
| | | • | Quarks are fundamental particles | | • | Quarks have charge and flavour | | • | Normal matter is made from only two flavours of quark - up and down | | • | Protons and neutrons are made of up and down quarks | | • | There are three fundamental forces in the story so far | | • | Leptons, including electrons, do not feel the strong nuclear force |
|
| | |
| | |
| |  |
| | | |
| | |
