Why do the rear tires of RWD car turn freely when lifted ground auto trans is in park?

When a rear-wheel-drive (RWD) car's rear wheels are lifted off the ground and the automatic transmission is in Park, the wheels turn freely because the parking pawl (the mechanism that locks the transmission in Park) is only engaging the output shaft of the transmission, *not* the driveshaft that connects to the rear wheels.

Here's a breakdown:

* Automatic Transmission in Park: The parking pawl engages a ratchet mechanism within the transmission, preventing the output shaft from rotating. This prevents the car from rolling.

* Driveshaft Connection: The output shaft of the transmission is connected to the driveshaft, which then transfers power to the rear differential and ultimately the wheels. However, the parking pawl's locking mechanism only directly interacts with the output shaft.

* Differential and Wheels: The differential allows the wheels to rotate at different speeds (e.g., when cornering). When the transmission is in Park, the differential is free to rotate because it isn't receiving any power from the transmission.

In essence, the parking pawl prevents the transmission from turning, but it doesn't mechanically lock the rear wheels themselves. Since the wheels are lifted, there's no resistance from the ground, and they can therefore spin freely even though the transmission is in Park. If the car were on the ground, the wheels would be prevented from turning (or at least significantly resisted) because the weight of the car would be resisting any rotational force.