Why the baseball flies farther on muggy days
There are many weather factors that can impact a baseball game. Most are obvious, rain, wind, even temperature ( at least to the players) but you might be surprised if I told you the ball will fly farther on a muggy day because the air is lighter.
Let's assume everything else is equal, temperature and wind speed at a ball park. The only thing we'll change is the moisture content of the air.
First let's look at what makes up the air we breathe. Our atmosphere is made up primarily by nitrogen, and inert gas, oxygen and then everything else. The one thing that varies is water vapor. It can range from near zero in the arctic to five percent in the steamy tropics.
You might remember from chemistry class every element has unique properties, including an atomic weight. Hydrogen is the lightest element with an atomic weight near one. Nitrogen and oxygen are much heavier than hydrogen.
A molecule of nitrogen gas is called N2 because it's two atoms of nitrogen. O2 is two oxygen atoms and H2O is two hydrogen atoms and one oxygen to form water.
So giving a certain mass of air. There can only be so many molecules, the only thing that changes is the number of H2O's. Given that water is much much lighter than N2 and O2, muggy air that has A LOT more water in it is lighter / less dense.
If you think about density think about the old riddle " Which is heavier, a ton of feathers or a ton of bricks?" The answer is of course they weigh the same. But you can push your way more easily through feathers than bricks. A baseball will have an easier time lifting high into the sky and over the wall on a muggy day.