- #1

Biloon

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I'm very confuse about the idea of applying Newton's law of forces and torques on rolling body. The book shows that you can separate the situation in rolling into pure transition and pure rotation. However, what I don't get is, for the calculation of Newton's 2nd law of forces on pure transition, they calculate all forces, not just the one through center of mass... If what I remembered, the forces that are not through center of mass should create both rotational and transitional kinetic energy, right? In case of rolling, the 2nd law simply applied as sigma F = ma, where F is applied anywhere on the body.

From that equation, I got myself into some contradiction. In case 1, If i have a Force F applied on the center of mass, then it accelerates with F = ma. In case 2, if the force is not directed on the center of mass, and if I follow the book, the book simply use Newton 2nd law of forces and torques... so my accelerations remain the same but with some extra torque. Therefore, for the same amount of force and over certain period of time, both cases will not have the same kinetic energy...

From what I believe, the force that is not on the center of mass will be distribute into rotational and transitional kinetic energy. However, the book simply applied full magnitude of forces not through center of mass for Newton 2nd law in rolling motion; that is really disturbing for me.

From that equation, I got myself into some contradiction. In case 1, If i have a Force F applied on the center of mass, then it accelerates with F = ma. In case 2, if the force is not directed on the center of mass, and if I follow the book, the book simply use Newton 2nd law of forces and torques... so my accelerations remain the same but with some extra torque. Therefore, for the same amount of force and over certain period of time, both cases will not have the same kinetic energy...

From what I believe, the force that is not on the center of mass will be distribute into rotational and transitional kinetic energy. However, the book simply applied full magnitude of forces not through center of mass for Newton 2nd law in rolling motion; that is really disturbing for me.

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