how can I vary the speed of a 110 volt electric motor?
You would need to use a "universal wound" AC motor, the type of motor found on sewing machines and in portable power tools. you could control the speed by using a simple rheostat like the ones used in the older pedal control for electric sewing machines or in the trigger switch on a portable, variable speed electric drill. the problem is finding one with the torque needed to power your load. You told us the speed you want to drive your load at. The size of the motor you will need, its horsepower rating and torque rating, will depend on what you are using it to drive.
