In this video from EdisonTechCenter, they explain in detail how the Tesla Model S operates using its 3-Phase, 4-Pole induction motor.

The motor is roughly the size of a watermelon and, like all electric motors, has 100% torque ready to go at any time with no need to shift gears as the Model S has a 1-speed gear box.

For the Model S, this motor combined with the 1-speed gearbox means that there's no acceleration lag all the way to the vehicle's top speed.

Check out the video for more details on the Model S' electric motor.