The Shape of the Earth
What happens if you take a ball of pizza dough in your hands and begin spinning it in the air? As the dough spins around in quick circles, centrifugal forces tug at the sides of the dough. This causes it to become flatter and flatter. The sides of the ball push further out until you have a flat disk rather than a ball.
Pizza dough is soft and easily flattened with just a small amount of force. Our planet is not soft. Its outer layers are made up of a hard shell-like crust of rocks and dirt. Even though the Earth rotates much faster than the ball of pizza dough, the Earth still remains relatively round. However, this spinning of the Earth does make it somewhat less round at the top and bottom. The difference is real but barely noticeable, making the Earth look more like a slightly flat basketball.
Many topographic differences also affect the overall shape of the Earth. From the lowest place on the surface of the Earth, the Mariana Trench, to Mount Everest, the highest mountain peak on our planet, there is a sizeable difference in height. The Mariana Trench, which lies at the bottom of the ocean, is 35,810 feet (10,915m) below sea level. Mount Everest is 29,028 feet (8848m) above see level. This is a difference of 64,838 feet, or roughly 12 miles (19km).
While this difference seems very large on a human scale, in reality, it is miniscule. If, for example, the Earth were the size of a basketball, it would be difficult for someone to find the bump that represented Mt. Everest, or to find the fold that represented the Mariana Trench. They would both be smaller than the thickness of a piece of paper. If all the mountains, valleys, and streams were accurately represented on the basketball, it would still feel very smooth to the touch.