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Hi. It's Mr. Andersen and this is AP Physics essential video 2. It is on fundamental particles
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which are particles that have no internal structure. So if I were to ask you the following
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question, this is a sample of pure iron, if I were to say is that a fundamental particle?
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Hopefully you would say no. You know that iron is made up of atoms. Now is the atom
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a fundamental particle? No. You know that an atom is made up of an atomic nucleus surrounded
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by these negative electrons. And so are those fundamental? Well you know that the nucleus
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itself is made up of protons and neutrons. And if we look into those protons and neutrons,
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you may not know it but they are made up of quarks themselves. A proton is made up of
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two ups and one down quark. And a neutron is made of two downs and one up quark. And
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so when we finally get to the level of quarks and electrons we are at the level of fundamental
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particles. In other words particles in physics that have no internal structure. And so atoms
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are made up of subatomic particles, electrons, protons and neutrons. And not all of these
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are fundamental particles. And so an electron is because it has no internal structure. But
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protons and neutrons are made up of quarks. And those quarks themselves have no internal
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structure. And so they are fundamental but the protons and neutrons are not. Now when
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we get to the level of the quarks we will find that they have properties like mass and
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spin and charge. And we can sum up those charges and it tells us a lot about the overall charge
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of the protons and the neutrons. What are some other fundamental particles? Photons
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are going to be little quanta of light or electromagnetic radiation. Neutrinos are another
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type of fundamental particle. And so what makes up matter at the smallest level are
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these fundamental particles. And so you can think of that cube of purified iron as a system
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made up of other objects. And we have to dig into that system to find the most fundamental
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of those objects. We know that in a sample of iron there are going to be 26 protons.
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And then we are going to have about 30 neutrons in a typical nucleus. As we zoom into that
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we finally get our first fundamental particle, the electron. But we have to dig farther into
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the proton and the neutron to find the fundamental particles, those quarks on the inside. And
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so here is a data set on an up quark and a down quark. You can see what their mass is,
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what their charge is and then what their spin is. And so if I want to figure out what is
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the charge of a proton, I am going to have to add up all three of these fundamental particles.
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And so if I take the charge of two up quarks, two-thirds times two, that is four-thirds.
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And then I am going to subtract the charge of one down quark, which is going to be four-thirds
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minus one-third, I get three-thirds or a positive one charge of a proton. It is coming from
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those fundamental particles. Likewise with the neutron, we have got one up, which is
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two-thirds positive charge minus two one-third charges for the two down quarks. And so a
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neutron is going to have no charge. And is if you are trying to ask a question about
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the behavior of protons and neutrons at this really really tiny level we have to understand
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what they are made up of. We have to understand these fundamental particles. And so physicists
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have come up with this standard model of understanding matter at the subatomic level. And it has
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spawned all these fundamental particles. Some you are totally familiar with. And so we have
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an electron for example or a photon. Some you have just heard a little bit about like
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these six types of quarks that make up matter. But some are brand new to you and are brand
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new to science. For example the top quark was discovered in 1995. The tau neutrino is
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2000. And if you have been reading the paper, the Higgs boson was discovered in 2013 using
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the Large Hadron Collider. And so you do not have to memorize all of the charges and masses
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or names of these fundamental particles. But you should understand this, the difference
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between a fundamental particle such as a quark, and a system composed of fundamental particles
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like an atom itself. And I hope that was helpful.