Free physics notes and video lessons

Recently added video lessons and pages include:

Strange particles, what are they and why are they strange? Strange particles and strangeness is a topic in most more advanced physics courses. The explanation here explains what a strange particle is, why it was called strange. How strange particles are produced and how they decay. The explanation centres upon the most common examples of strange particles, the kaons.

Pair production In the notes and video is explained that pair production and annihilation are opposite processes converting the energy of a photon into mass and the reverse. The video tutorial explains the processes using animation and in terms of Feynman diagrams. Finally there is a sample calculation of the frequency of the photon that would be required for pair production.

Carbon dating Carbon dating is based on the amount of carbon 14 in a sample of organic material. The age of the organic material is judged by the amount of activity of the carbon 14 which has a long half life. The video explains how carbon 14 is formed and how it enters the food chain. It goes on to explain how the age of an organic sample can be calculated from the measured activity.

Baryon number and conservation The video with supporting notes explain what the baryon number is, which particles it usefully applies to and how it is calculated, with examples.

Nuclear density, a million tonnes in a teaspoon notes and video. The video and notes are in three parts. Firstly a general explanation of why nuclear material is so dense. The second part is a calculation of nuclear density using a carbon nucleus as an example. The third part is a brief summary of the characteristics of a neutron star.

Are neutrons stable?      The notes and video explains to A level standard (16 to 19 physics students) that neutrons are a fundamental part of all atoms (except hydrogen). They enable the atom to be stable "diluting" the repulsive forces between the positively charges protons. Within the atom the neutrons are mostly stable, but not always. Outside the atom free neutrons are always unstable, decaying with a half life of about 10 minutes.

Muon decay and relativity: Video and notes explaining what a muon is and how the measured rate of decay is useful in supporting Einstein's theories of relativity.

Gauge bosons, the glue that holds everything together. The video and notes give a brief introduction and description of the four particle carriers of the four forces recognised in the standard model. The photon conveying the electromagnetic force. The graviton (the existence of which has not been confirmed in practice) conveying the gravitational attraction between particles of matter. The gluon conveying the strong force and W plus, W minus and Z bosons responsible for the weak force.

Fermions The video explains that this group of particles includes the fundamental leptons and quarks as well as the quark composites called hadrons. Fermions are the building blocks of matter. The video lesson describes the main properties of each and provides useful summaries.

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