Simplify the following text for a Grade 7 native English-speaking person.
Original: The speed and rate of rotation of the fluid in a free ( irrotational ) vortex are greatest at the center , and decrease progressively with distance from the center , whereas the speed of a forced ( rotational ) vortex is zero at the center and increases proportional to the distance from the center .
Simplified: The speed and rate of rotation of the fluid are greatest at the center and become smaller with distance from the center .