The planets are like a ball attached to a string which is attached to a pole.
As the planet aproaches the Sun, it strong wraps around the pole causing the ball to move faster, when the planet comes back from behind the Sun the volicity it has causes it to move away from the sun very quickly, out into space as far as the string allows it then it starts coming back towards the sun with the string wrapping around the pole.
Thus making its orbit eliptical with the Sun at one focus point.
