What is Pseudoforce?
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Imagine that you are in a car accelerating. You feel pushed into the back of the seat. Now if an outside observer look at the car they see that because you have inertia, in order to accelerate the car must put a force on your body. The back of the seat accelerates your body. The resulting force you feel comes for your body resisting a change in motion. Thats inertia.
From your reference frame inside the car, you feel this force on your body. Which means that this F=ma doesn’t work. There is a force acting on object without apparent acceleration. This acceleration is acceleration you measure inside your reference frame. In other words in order to keep something stationary you have to apply a force. This apparent force that pushes object towards the back of the car isn’t real. If you change your reference point to be an outside observer, you see the car accelerating and objects trying to remain still, until something forces them to accelerate.
Imagine it like this, you are in a spaceship floating in space. There is a ball in the ship. The ship accelerates and the ball moves towards the back of the ship. From an inertial reference frame the ball moves towards the back because nothing is making it move with the spaceship. It doesn’t move, its stays still, the ship moves. But inside the ship it looks as though there is a force pushing that ball to the back. Thats a fictitious force or pseudo force.
We can introduce pseudo forces to model the movement of objects inside an accelerated frame of reference. In this case if the ship accelerates with a0 the equation would look like this F=m×a+m×a0. So if inside the spaceship you see that nothing accelerates the ball you have F=m×0+m×a0, F=m×a0. That is the pseudo force, you model the accelerated frame of reference with fake forces. If you want to make that ball sit still from the ship’s point of view you must apply a force in the opposite direction so the sum of forces will be zero. 0=m×-a0+m×a0, 0=m(a0-a0). From this another way to look at it is that if there isn’t apparent acceleration you feel forces. F+m×a0=m×a. So when you got F+m×a0=m×0, F cannot be 0. It must be -a0×m. If you want no apparent acceleration you need a force.
Pseudo forces are required to model accelerated frames of reference. This example was about translation but there is rotation. In a rotating frame of reference there are 3 pseudo forces: centrifugal force, Coriolis force and Euler force.
F=m×a works in inertial reference frames for accelerated frames of reference this definition must be modified. And the things we add to it are pseudo forces.
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