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--- 183_notes:angular_motivation [2021/05/08 18:46] – [Catching a Ball] stumptyl
+++ 183_notes:angular_motivation [2021/05/31 15:47] (current) – [An Observation You Can't Fully Explain] stumptyl
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+//This video is primarily used for visual learning. No audio is within this demonstration video.//
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-This is an inelastic collision. You have read how to [[183_notes:colliding_systems#inelastic_collisions|deal with this kind of collision]] and you can explain this observation relatively well with conservation of momentum and energy.
-  * The frictional force by the floor is large enough to keep the stool and the sitting person from sliding away. That is, for the system of the sitting person, the ball, and the stool, there is an external force by the floor that changes the momentum of that system.
+**This is an inelastic collision.** You have read how to [[183_notes:colliding_systems#inelastic_collisions|deal with this kind of collision]] and you can explain this observation relatively well with conservation of momentum and energy.
+  * The frictional force by the floor is large enough to keep the stool and the sitting person from sliding away. That is, for the system of the sitting person, the ball, and the stool, __//there is an external force by the floor that changes the momentum of that system.//__
  $\Delta \vec{p}_{sys} = \vec{F}_{ext}\Delta t$
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 With estimates of the velocity and mass of the ball as well as the collision time, you can determine the frictional force that the floor exerts on the stool.
-  * The collision is inelastic, so the kinetic energy of this system is not conserved, which is fairly obvious. Initially the system has kinetic energy (the ball is moving) and in the final state it does not. The system's internal energy has increased as a result. Because there is no displacement, the floor does no work. We can further assume (as we have in other collisions) that there is no exchange of energy due to a temperature difference.
+  * The collision is inelastic, so the kinetic energy of this system is not conserved, which is fairly obvious. Initially, the system has kinetic energy (the ball is moving) and in the final state, it does not. The system's internal energy has increased as a result. Because there is no displacement, the floor does not work. We can further assume (as we have in other collisions) that there is no exchange of energy due to a temperature difference.
  $\Delta E_{sys} = W_{surr} + Q$
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 {{youtube>dOIrX12UXQU?large}}
+//This video is primarily used for visual learning. No audio is within this demonstration video.//
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 Now, when the ball is caught, the person in the stool begins to rotate. There are a few other observations that you can make (depending on how much friction is in the bearings):