(20 13? Xiaowen has a jet dolphin toy car (pictured). The air from the top can lift the ball to a certain height and the car will move.

When the airflow is ejected, the speed of the air increases, which will cause the pressure change here, which is less than the surrounding pressure, so the ball will not deviate easily. Once it deviates, the surrounding pressure will push it back.

So the answer is: fluid pressure (or flow);

If the ball deviates from the top of the airflow, the air near the airflow has high speed and low pressure, while the air far away from the airflow has low speed and high pressure, and the ball will be pushed back to the top of the airflow.