Great questions!

What causes weather changes? The temperatures changes during the season because the earth is tilted on its axis. The sun is more effective at heating different parts of the earth during different parts of the year. Major precipitation events occur when there are changes or gradients in humidity, pressure, and temperature.

A small experiment which may articulate my idea is using food coloring, room temperature water, cold water, and hot water. If you dye the cold water and hot water different colors then add it to room temperature water one will see the hot water stays near the top and cold water falls to the bottom.After a long enough time though the temperature equilibrates and the hot, cold, and room temperature water will be evenly mixed.

Cold air is denser and moves further to earth, while hot air rises.

Is the world a real sphere? It is not a sphere but rather an ellipsoid. The earth bulges at the equator. Gravity and the centrifugal force explain the ellipsoid shape. If a large enough mass is left alone, gravity will cause the mass to become a sphere.

Having enough mass to form a sphere due to gravity is a criteria to being classified as a planet according to the International Astronomical Union

The earth is not a stationary being in space. It is spinning around its axis. When a body of mass is spinning it experiences something called the centrifugal force.

For example, when one spins pizza dough that started as a sphere it becomes flat. The centrifugal force pulls the dough away from the sphere. The earth’s shape arises because gravity wants to make the earth a sphere but the centrifugal force wants to make it flat. Thus, the earth bulges slightly at the equator.

According to NASA the earth is about 21 km flatter at the poles click here please