Hi. I don't really get the concept of back emf, especially in this question. Any help would be appreciated, thanks.

A to}:r car with a DC motor is connected to a 9 V battery. A child switches on the car while it is held inthe air and the motor starts to spin freely. The car is then placed on some grass and the car starts to move. As the grass gets caught in the axle of the wheels, the motor stops spinning. The child picks up the car and switches off the motor. Describe the changes to hack EDUIF that occur to the motor during this time. Description of back EMF Car is switched o' Car is switched on an held in the 1-111" Car is moving on grass Car is switched o