Centrifugal force is fictitious force.Why is it called fictitious force ...

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Let's assume that you are driving a truck with constant velocity (same speed and same direction). Next to you on the truck seat/bench is a basketball. While you are buckled in, the basketball is not. As you and the truck approach an intersection, you decide to make a left turn. As you make the left turn, the basketball on the truck bench begins to roll to the right, away from you, towards the passenger door. The basketball makes contact with the door and the door stops the basketball as you continue the left turn. So what happened to the truck and the basketball in terms of forces? Newtons 2nd law states that only a net force can change the constant velocity of an object. For the truck, the net force that changed its velocity is the force of friction between the tires and the road. Since you were attached/glued/part of the truck by holding on to the steering wheel and buckled in by your seat belt, you had no choice but to move left with the truck. However, the basketball moved to the right, as if some "net force" changed its motion. This so called "net force" is known as the centrifugal force. In reality, the basketball was following Newton's 1st law of motion. The 1st law states that objects at rest or moving with constant velocity want to keep doing that, to be at rest or to move with constant velocity until a net force changes their condition. The basketball was not part of the truck like the driver. So the basketball continues to move in the original straight line of the truck until it makes contact with the door and then the door applies a force to it making it move to the left. The ball rolled to the right due to its inertia or mass. The ball "wanted" to continue in a straight line with constant speed. There was not a force that made it move to the right. Inertia made the basketball continue in a straight line and thus appear to move right as if some force moved it. That is why the centrifugal force is fictitious. It does not exist. From a frame of reference point of view, the truck moved left compared to the road while the basketball did not deviate from its straight line path compared to the road. When you compare the basketball to the driver, the ball moved right as if some "force" moved it. However, it was not a force, it was inertia. It resisted going left until the door forced it to go left.