According to the formula: v=St, we can know that V is above > V is below, that is, the speed of air above the car is greater than that below the car.
In fluid, the greater the flow rate, the lower the pressure, so the gas pressure above the car is lower than that below the car.
Force analysis of automobile in vertical direction;
Since the gas pressure above the car is less than that below the car, there are downward gravity G, upward car support force F and upward air pressure F..
The car is in equilibrium in the vertical direction, that is, it is subjected to a balancing force, so G=F branch +F pressure, and the deformation is: F branch =G-F pressure. The greater the vehicle speed, the greater the upward and downward pressure difference, that is, the greater the F pressure.
In the formula f branch =G-F pressure, g is a constant, and the f branch becomes smaller because the f branch becomes larger.
Because the pressure of the car on the ground and the supporting force of the ground on the car are acting force and reaction force, which are equal.
Therefore, the pressure of the car on the ground is also reduced.
So, the answer is: big; Small; small