Why does a car roll on flat ground when parked?

[Layla]

After an automatic car is parked on a level surface, the reason for rolling may be that the handbrake was not engaged. It could be because the vehicle was stopped without first engaging the P gear, and the second reason might be that the electronic parking brake was not activated. To prevent the car from rolling when parked, drivers should first shift to P gear, then engage the handbrake, and finally turn off the car key. Here are some additional notes: If the torque transmitted from the engine to the tires gradually increases, and the clutch is fully released, the rolling phenomenon will no longer occur. Then, after reaching the semi-engagement point, the engine starts to deliver torque to the tires, and the car can gradually start moving as the clutch is lifted.