## 5 thoughts on “5.57”

1. Andre says:

Why do we use k_theta2 instead of k_theta4?

1. tutorpaul says:

I don't entirely understand your question, $k_{\theta_4}$ was never defined in the solution.

Are you asking why $k_{\theta_2$ was chosen as the name for the stiffness of the shaft between the disk labeled $I_4$ and the one labeled $I_5$ instead of $k_{\theta_4}$? If so, I don't have a good answer. It needed a name and I grabbed the first one that came to mind.

2. Andre says:

Oh okay, I thought it was defined for the gears but I see now the spindles themselves are 2 and 3.

3. ek337335 says:

what is the methodology behind the contact forces on the gears? I got the directions wrong.

1. tutorpaul says:

The methodology is basically Newton's third law. We know that there is a force at play between the two gears, thus we should suppose they are equal and opposite. The actual direction we assume them to be pointing is irrelevant (the math may tell us that the magnitude of the force is negative and thus correct our assumption); what does matter is that we draw the forces as equal but opposing.