# How to find the Braking Torque of an Eddy Current Braking Setup?

#### IndianGeek234

Density?!
Thinking of it as mass was only an analogy so that you could know to apply the moment of annulus formula, or parallel axis theorem, or whatever.

In post #14 you had $\sigma\omega\tau r^2B^2\int dA$.
But the r should have been inside the integral: $\sigma\omega\tau B^2\int r^2dA$.
That integral is the second moment of area (like moment of inertia, but without the density factor), and in post #23 I gave you the solution for this when it is an annulus:
had $\sigma\omega\tau B^2\frac 12\pi(r_2^4-r_1^4)$.
But your shape is only half an annulus, so $\sigma\omega\tau B^2\frac 14\pi(r_2^4-r_1^4)$.

Hihi,

So sorry for the delay,

I tried again with this new value. It's still giving me way too high values for the torque. I'm really stuck now. Everything in the equation looks fine but it's just the $\sigma$ which drives up the torque numbers a lot.

#### haruspex

Homework Helper
Gold Member
2018 Award
Hihi,

So sorry for the delay,

I tried again with this new value. It's still giving me way too high values for the torque. I'm really stuck now. Everything in the equation looks fine but it's just the $\sigma$ which drives up the torque numbers a lot.
Please post the details, the numbers for the different variables and your working.

"How to find the Braking Torque of an Eddy Current Braking Setup?"

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