12 Particles Of Matter And 4 Forces Of Nature...

Seeing Professor Brian Cox on A Night With The Stars last night reminded me that I had not finished writing this post about the fundamental particles of matter.  The idea came from a video that quotes Prof Cox in the chorus referring to the twelve particles of matter and the four forces of nature. Many of you know that the four forces of nature are: gravity, electromagnetism, the weak nuclear force and the strong nuclear force.

Four Forces Of Nature

Gravity is the very weak force of attraction that exists between all objects. The more massive the object, the greater the force. Gravity on Earth is about 10N/kg – so every kg of your matter is pulled towards the centre of the Earth with a force of about 10 Newton. You can read a little bit more about it on this blog by starting here or by searching for the word gravity. The moon, which is a quarter the size of the earth has a gravitational force just 1/6th  that on Earth – so your weight on the moon would be just 1/6th what it is on Earth. You would definitely be able to set a high jump personal best.

The electromagnetic force exists between charged particles. It is the force responsible for electric current, magnetism and light (a form of electromagnetic radiation). Any wire carrying a current also has a magnetic field around it. You can find out more about electromagnets from this blog post. It is the force that gives you an electric shock from the static charges built up by a Van Der Graaf generator; it is also the force that prevents you from passing your hand through solid objects.

Then there is the more mysterious ‘strong force’. This is the force that holds protons and neutrons together. Its effect, unlike gravity or the electromagnetic force, are local; it doesn’t reach outside the proton or neutron. Protons are positively charged particles in the nucleus of atoms, neutrons are (as the name suggests) neutral so have no overall charge. Between them they give atoms their mass. For example, a hydrogen atom has one proton in its nucleus so we say that the relative mass of hydrogen is 1. A carbon atom has six protons and six neutrons so the relative atomic mass of carbon is 12.

The last fundamental force of nature is known as the weak force (or weak interaction). Like the strong force, this acts at the subatomic level so we don’t experience it directly. It is the force that is responsible for atomic decay and radiation. It is also the force that allows hydrogen atoms to fuse into helium inside stars. This last process is the one that produces all the sun’s light and heat so it is quite important! You can read about the Sun here and about nuclear fusion more generally here.

Twelve Particles Of Matter

Giving you a clear definition of the 12 fundamental particles of matter is less simple because for every statement a lengthy explanation seems to be needed. Physics uses something called the standard model, to describe the 12 fermions that make up the basic set of particles. These twelve fermions are divided into two sets of six quarks and six leptons. The quarks are called up, down, strange, charm, top and bottom. The leptons are called the electron, electron neutrino, muon, muon neutrino, tau and tau neutrino.

There are also the force carrying particles called bosons. They are photons (responsible for the electromagnetic force), W and Z bosons that cause the weak force and gluons that result in the strong force. There may also be a boson caused the Higgs boson that would help to explain gravity.

Thus, a proton is made from two up quarks and a down quark held together with gluons. A neutron is built from two down quarks and an up quark, again with gluons providing the force that holds them together. The large hadron collider at CERN accelerates protons to a fraction of the speed of light and smashes them up in detectors that can see the quarks, leptons and bosons flying out of the wreckage. You can read a little more about the LHC here.

Questions…

1. Suggest three ways you could make the electromagnet shown above stronger.
2. Name a force (not mentioned above) that tends to oppose motion and often results in the production of heat.
3. A man has a mass of 76kg on earth. What would his mass be (a) on the moon (b) in deep space? What would his weight be (in Newton) (c) on the moon (d) in deep space?
4. How fast do photons travel through a vacuüm (choose your units!)?