# Power to overcome bearings resistance

1. Mar 31, 2014

### Sunfire

Hello,

I have a pair of bearings (NSK Super Precision Angular Contact Ball Bearings) and was wondering whether I would be able to estimate the power it takes to overcome the bearings resistance when the shaft spins with some given rpm.

Are you aware if this is possible to estimate. Thanks!

2. Mar 31, 2014

### AlephZero

Download the product catalog from the NSK website. That has the technical data to answer the question.

3. Mar 31, 2014

### Sunfire

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4. Mar 31, 2014

### AlephZero

... and the formula using the factor f_0 is in Part 5 Section 6.

5. Apr 1, 2014

### Sunfire

Thank you

The dynamic torque is given by a load term and a speed term.
The speed term is:
$M_v = f_0 (v_0 n)^{2/3} d_m^3$, but its dimensional analysis has left me wondering.

$M_v$ - dynamic torque, dimension [N.m]
$f_0$ - some factor, dimensionless
$v_0$ - kinematic viscosity, [$m^2$/s]
$n$ - speed, [???]
$d_m$ - pitch circle diameter of rolling element, [m]

Lhs requires a [kg] to appear somewhere in the Rhs. Probably something is amiss with the above expression. I cannot imagine [kg] has anything to do with the "speed" $n$?