Why is the image of quadratic function a parabola

Why is the image of quadratic function a parabola

According to Niu Er's law, we can get that the trajectory of a parabola is a quadratic function!
Law content: the acceleration of an object is directly proportional to the combined external force F, inversely proportional to the mass of the object, and the direction of acceleration is the same as that of the combined external force,
Newton's second law of motion
In other words, the first derivative of momentum to time is equal to the sum of external forces