# How Is an Atom Similar to & Different From the Solar System?

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An atom is similar to the solar system in that they both essentially have a nucleus. Find out about how an atom is similar to and different from a nucleus with help from an applied physics professional in this free video clip.

Part of the Video Series: Such Great Physics
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## Video Transcript

Hello, my name is Walter Unglaub. And this is how is an atom similar to and different from the solar system. So, here I have two diagrams, one of a solar system and one of an atom. And while there are some similarities, there are certainly more differences than there are similarities. So, first let's look at the similarities. We see that both a solar system and an atom have a nucleus. In the case of the solar system, it's a star or in our solar system we call it the Sun. And in an atom the center is the nucleus, which is made up of protons and neutrons. A star is also made up of protons and neutrons, mainly hydrogen and helium. So we see that both are composite objects, meaning they have a nucleus and objects that orbit around them. So that's one similarity. Another similarity is that both contain nearly all of their mass at the center. So all of the mass, almost in the center. And another similarity is that they both have orbiting objects. So in the case of the solar system, they're called planets or more generally just satellites. And in the case of the atom, they're called electrons, these fundamental particles. And one final similarity is that both have this notion of conservation of angular momentum, which arises from certain types of symmetries. Here a symmetry about the rotation axis. Now, let's discuss the differences. There are very fundamental differences between these two types of composite objects. One difference is that a solar systems' dynamics are governed and dominated by gravitation. Where as the dynamics of an atom is dominated by electromagnetic forces and quantum mechanics, Em and QM. Another big difference is that the atom actually has two types of angular momentum. Whereas a solar system just has orbital angular momentum in the system. An atom can also have spin angular momentum. So in addition to orbital, it also has spin. And spin angular momentum in quantum mechanics is something that is inherently quantum mechanical. No classical object such a solar system has this property. Because spin, there is no classical analog for this, this is a quantum property that is inherent in all quantum particles. My name is Walter Unglaub, and this is how is an atom similar to and different from the solar system.

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