None of the giant planets are truly round. Explain why they have a flattened appearance.

The rotation of giant planets such as Jupiter, Saturn, Uranus, and Neptune occurs much faster compared to Earth. For instance, while Earth takes 24 hours to complete one rotation, Jupiter manages to do it in just about 10 hours. This high-speed rotation significantly influences the planets' overall shape and appearance. Rotational speed impacts the redistribution of mass within the planet, especially at the equator and poles.

Centrifugal force is a result of the fast rotation of the giant planets. When a planet rotates, any point on its surface moves in a circular path. Due to this motion, there is an outward force experienced by the materials of the planet, pushing them away from the axis of rotation.
This force is stronger at the equator and virtually non-existent at the poles. The effect of centrifugal force is to make the planet 'bulge' at the equator and become flatter at the poles. The faster the rotation, the greater the centrifugal force, and thus, the more pronounced the bulge.
On Earth, centrifugal force has a minor impact owing to its slower rotation. However, for giant planets with significantly faster rotations, the effect is substantial and crucial in shaping their appearance.

As a result of fast rotation and the centrifugal force, giant planets develop an oblate spheroid shape. Unlike a perfect sphere, an oblate spheroid is slightly flattened at the poles and bulged at the equator.
Imagine squeezing a soft rubber ball along its axis. The ball would flatten at the points where you apply pressure (the poles) and expand in the middle (the equator). This is essentially what happens to giant planets due to rapid rotation and centrifugal force.
The concept of oblate spheroid helps explain why none of the giant planets appear truly round. Their rotational characteristics, combined with the forces experienced due to this rotation, result in an equatorial bulge and polar flattening. This gives them their distinctive 'flattened' shape seen in images and observations.