Name: 基本粒子 (Fundamental Particles)
Uploaded: 2021-01-14T05:01:28.000Z
Duration: 4 min 20 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。

Hi. It's Mr. Andersen and this is AP Physics essential video 2. It is on fundamental particles

關係子句

which are particles that have no internal structure. So if I were to ask you the following

question, this is a sample of pure iron, if I were to say is that a fundamental particle?

Hopefully you would say no. You know that iron is made up of atoms. Now is the atom

a fundamental particle? No. You know that an atom is made up of an atomic nucleus surrounded

by these negative electrons. And so are those fundamental? Well you know that the nucleus

itself is made up of protons and neutrons. And if we look into those protons and neutrons,

you may not know it but they are made up of quarks themselves. A proton is made up of

two ups and one down quark. And a neutron is made of two downs and one up quark. And

so when we finally get to the level of quarks and electrons we are at the level of fundamental

particles. In other words particles in physics that have no internal structure. And so atoms

are made up of subatomic particles, electrons, protons and neutrons. And not all of these

are fundamental particles. And so an electron is because it has no internal structure. But

protons and neutrons are made up of quarks. And those quarks themselves have no internal

structure. And so they are fundamental but the protons and neutrons are not. Now when

we get to the level of the quarks we will find that they have properties like mass and

spin and charge. And we can sum up those charges and it tells us a lot about the overall charge

of the protons and the neutrons. What are some other fundamental particles? Photons

are going to be little quanta of light or electromagnetic radiation. Neutrinos are another

type of fundamental particle. And so what makes up matter at the smallest level are

these fundamental particles. And so you can think of that cube of purified iron as a system

made up of other objects. And we have to dig into that system to find the most fundamental

of those objects. We know that in a sample of iron there are going to be 26 protons.

And then we are going to have about 30 neutrons in a typical nucleus. As we zoom into that

we finally get our first fundamental particle, the electron. But we have to dig farther into

the proton and the neutron to find the fundamental particles, those quarks on the inside. And

so here is a data set on an up quark and a down quark. You can see what their mass is,

what their charge is and then what their spin is. And so if I want to figure out what is

the charge of a proton, I am going to have to add up all three of these fundamental particles.

And so if I take the charge of two up quarks, two-thirds times two, that is four-thirds.

And then I am going to subtract the charge of one down quark, which is going to be four-thirds

minus one-third, I get three-thirds or a positive one charge of a proton. It is coming from

those fundamental particles. Likewise with the neutron, we have got one up, which is

two-thirds positive charge minus two one-third charges for the two down quarks. And so a

neutron is going to have no charge. And is if you are trying to ask a question about

the behavior of protons and neutrons at this really really tiny level we have to understand

what they are made up of. We have to understand these fundamental particles. And so physicists

have come up with this standard model of understanding matter at the subatomic level. And it has

spawned all these fundamental particles. Some you are totally familiar with. And so we have

an electron for example or a photon. Some you have just heard a little bit about like

these six types of quarks that make up matter. But some are brand new to you and are brand

new to science. For example the top quark was discovered in 1995. The tau neutrino is

2000. And if you have been reading the paper, the Higgs boson was discovered in 2013 using

the Large Hadron Collider. And so you do not have to memorize all of the charges and masses

or names of these fundamental particles. But you should understand this, the difference

between a fundamental particle such as a quark, and a system composed of fundamental particles

like an atom itself. And I hope that was helpful.