Traction and friction? Isn't the traction of a car expressed as the friction between the ground and the car? And the friction is not only determined by the roughness and pressure? Is the heavier the car, the greater the traction? How to understand the relationship between traction and friction? I still don't quite understand, such as the same car. No matter what kind of engine is changed, the initial traction is the same, but the rated power is increased?

Traction and friction? Isn't the traction of a car expressed as the friction between the ground and the car? And the friction is not only determined by the roughness and pressure? Is the heavier the car, the greater the traction? How to understand the relationship between traction and friction? I still don't quite understand, such as the same car. No matter what kind of engine is changed, the initial traction is the same, but the rated power is increased?

One of your biggest misconceptions is that friction is only determined by pressure and roughness
As a matter of fact, only sliding friction is determined by pressure and roughness; static friction is driven force, which can be equal to any value smaller than the maximum static friction. (for example, if an object is placed on the table at rest, then static friction is 0. If a 1n force is used to push an object, if it is not pushed, the friction or static friction is equal to 1n. Similarly, if 2n force is used to push, if it is not pushed, Static friction is 2n, so static friction is not constant. It is different from sliding friction.)
1. The traction of a car is really the friction between the ground and the driving wheel
2. Then you have a misunderstanding: sliding friction is only determined by pressure and roughness; static friction is not. Static friction is driven force, which is always equal to the force balanced with it
Obviously, the tire will not slip on the ground, so there is static friction between the tire and the ground. What is the relationship between static friction and pressure and roughness? Pressure and roughness determine the maximum static friction
3. The heavier the car is, the greater the maximum static friction between the tire and the ground. However, the actual traction is not necessarily equal to the maximum static friction (generally smaller than the maximum static friction). How much it is equal to. Whether the maximum static friction can be achieved depends on the ability of the engine
4. How to understand the relationship between traction and friction? The maximum static friction between the tire and the ground is determined by the weight of the vehicle and the roughness of the tire. The maximum static friction represents the maximum power theoretically provided by the vehicle. The actual power depends on the traction provided by the engine
Supplementary question: if the tire is not changed and the vehicle weight remains unchanged, then the maximum static friction provided by the tire remains unchanged. For example, it is 1000N. Then the actual traction is determined by the engine. For example, if the original engine can provide 500N traction, then the vehicle's traction (actual static friction) is 500N; if the engine is changed, it can provide 800N traction, Then the actual traction force is 800N; if the 1200n engine is replaced, the maximum static friction between the tire and the ground is 1000N when the car starts, then the tire will slip, and the sliding friction is generally considered to be equal to the maximum meridional friction of 1000N