SIMPLIFIED: "12.3: Angular Momentum"

Link to article: https://phys.libretexts.org/Bookshelves/University_Physics/Book%3A_Introductory_Physics_-_Building_Models_to_Describe_Our_World_(Martin_Neary_Rinaldo_and_Woodman)/12%3A_Rotational_Energy_and_Momentum/12.03%3A_Angular_Momentum 

Note: The image above was taken from the original article.

The article linked above is all about angular momentum! Angular momentum is NOT the same as linear momentum, which is a topic that we have simplified on this website. Angular momentum is basically how hard it is to stop an object that is rotating. 

The linked article above has a lot of math and steps to get to the equation for angular momentum. Since our goal is to simplify these concepts, here is just the equation for angular momentum: angular momentum = moment of inertia * angular velocity. Angular momentum is detonated as L. Angular velocity is detonated as w, which is omega. Angular velocity, just like it sounds, is basically linear velocity but in rotational form; it is how fast an object is rotating, and the unit is radians per second. The moment of inertia can be seen as the rotational equivalent of mass, but it is a little bit more complicated to calculate because the way to calculate moment of inertia is different depending on the object. The moment of inertia is denoted as I in physics. 

There is also the conservation of angular momentum. Just like how linear momentum is conserved when there are no external forces acting on the system, angular momentum is also conserved when there is no net TORQUE acting on the system. 

You might ask, how come figure skaters sometimes extend their arms but sometimes bring their arms closer to their body while skating? This is because of angular momentum. When a skater extends their arms, their moment of inertia increases. Since their angular momentum has to stay conserved, if the moment of inertia increases, this means their angular velocity has to decrease. Therefore, if a skater wants to spin faster and faster, you will notice that they bring their arms closer to their body so that their moment of inertia decreases.