When a car is moving in a circle, I want to know how the friction of the car could be drawn. I have found the following picture. But I know that the friction force is always in opposite direction of the movement. I have copied the picture and on the right side I have drawn how the friction should be, in my opinion. Is that right? So if I get it right there are two frictions: Fr and Fs?
First of all, there are problems with the figures.
The centripetal force always acts towards the center of the circular motion. The centripetal force and the static friction force shown in the diagrams are one and the same. As viewed from the inertial (non accelerating) frame of reference of the road, there is no force acting outward on the vehicle. Only in the accelerating frame of the car, there is a fictitious outward force called the centrifugal force which is introduced to apply Newton's 2nd law to the accelerating frame. I have revised the figures as shown below to show the forces in the inertial frame of the road.
But I know that the friction force is always in opposite direction of the movement.
That only applies to kinetic friction, which is the friction force between the tires and the road if the tires are skidding on the road.
The static friction force prevents skidding and is responsible for (1) circular motion of the car where it is actually the centripetal force acting toward the center and (2) tangential acceleration and deceleration and acts in the same direction as the acceleration.
If the speed of the car is constant, then there is no tangential acceleration. If the car is accelerating (or decelerating) the static friction force responsible for the acceleration is in the same direction as the tangential acceleration, as shown in my figure to the right.
The blue force you shown in your figure is actually the force that the wheel is applying to the road. Per Newton's 3rd law the static friction force the road applies to the wheel is equal and opposite to the force the wheel applies to the road.
Hope this helps.
There is a static friction force from the road acting on the bottom of each tire. One component of this provides the centripetal force (and centripetal acceleration) toward the center of a circular curve. A forward component on the driven wheels acts to provide forward acceleration (when needed), opposition to fluid friction (from the air), and opposition to “rolling friction” (which results from deformation of the tires and road). When the breaks are applied, this component acts backward and is helped by the non-driven wheels. Under extreme breaking, the automatic breaking system may pulse the breaks to avoid kinetic friction which is smaller.
