Question

Why planets revolve around the sun in the elliptical path?

Answer 1

If you consider two circular orbits, one at the minimum radius and one at the maximum radius, the minimum orbital speed will be faster than the maximum orbital speed since the Sun's gravitational force decreases by the radius. However, when the Earth is at its minimum distance, it's speed will be faster than the corresponding minimum circular orbital speed - which is why it moves out to a larger radius. As the radius increases, the Earth will slow down such that when it reaches the maximum circular orbit radius, the Earth will be moving slower than that circular orbit. That is why the Earth will then fall further in towards the Sun to the minimum radius again. That is why the planets revolve around the sun in the elliptical path.