PWM frequency change

I am new to arduino and am trying to code a vibrating motor to vibrate at 100Hz, how do I go about changing the PWM so thats frequency is the value i want?

Thanks

If you provide some information about the motor and how you are controlling it, perhaps someone can guess an answer.

http://www.righto.com/2009/07/secrets-of-arduino-pwm.html

http://playground.arduino.cc/Code/PwmFrequency

http://arduino-info.wikispaces.com/Arduino-PWM-Frequency

If you really need 100Hz for it, rather than bit-banging or using a timer manually, you could consider the 'PWM Frequency Library'. Frequencies from 1Hz to 2MHz are possible.

The library:- 'PWM Frequency Library'

The Arduino documentation:- 'PWM Frequency Library' documentation

If its a rotary eccentric-mass motor then you'l have to experiment to find the drive level that takes it to 100Hz (ie 6000 rpm). It will depend a lot on the mechanical mounting of the motor.