How would you like to turn into gas for a day? You will get to float around and be free. You will get to fill up every space you go into. No one will be able to see you because you will be a million little parts. Ready? I will tap you on the forehead with this "Do Whatever I Want" branch. And there. You should now feel a little loose and a little wobbly as all of your parts start to spread around the room. Won't this be a gas? Get it? Ha ha ha. Why are you not laughing? Oh. Right. You're actually a gas now.
As a gas, you really know how to fill a room. You will spread from the ceiling to the floor and all around the walls. This is why we can smell if the oven has been on. It's how you can tell that something is burning.
Density is how much stuff is in a space or thing. As a person, your body is a lot of stuff in one space. The more you spread out as a gas, the less stuff there is in one space. Feeling claustrophobic? Does this room feel like a shirt that's too tight? Here. I'll open the window . . . Uh-oh.
This is something you can smell all over the house!
All of your parts go rushing outside, up up up into the sky. Since the ground outside the window is so hot, all the tiny parts of you get super hot too. As the gas parts of you get hot, they push away from each other. All the extra space makes you weigh less and less. The air near the ground is packed close together, so you float up to where other gasses are as spread out as you.
Convection is when heat makes things rise because they become less dense. That's right, heat makes you so excited, you can fly. You rise higher and higher and higher. Have I lost you? It depends on how hot it is outside . . . 93 degrees. Well, shoot.
Not only did these guys open their window; they opened up the whole roof!
When gas gets hot, its parts push apart and then start to crash into each other, bouncing away, and moving out and out and out and out. Think of rush hour at the train station or people leaving a crowded bus. To
expand means to spread out. There are no walls around you, so there is nothing to stop you from moving up and up and up and out and out and out. Right now, you are spreading out into the sky and mixing with the air.
A volcano knows how do deal with expanding gases.
McGimsey, Game, Public domain, via Wikimedia Commons
Phew. There's a cold front moving in. Your gas parts start to move slowly. This makes them bounce into each other more slowly and the parts start to come back together. Imagine all the people at the train station packing themselves back into a train. To
contract means to come together. When you cool down, you will start to feel more like yourself again. All your parts find each other and stay closer. Now that they are all close together again, you are more dense and this makes you fall down as a gust of wind. Wheeeeeeee!
Good thing I have this "Do Whatever I Want" branch. Aaaaaand there. You are back to being a person now. As a gas you act very different than anything else. When it's cold, you get a little heavy, come together a bit, but no one can see you. When it's hot, you rise up and up, filling the whole sky. When it's really hot, the Earth lets go and you rise as high as you can, only to drop back down as rushing wind. I just hope this did not leave you feeling too gassy! Ha ha ha ha ha. Still nothing? Sigh.
References: Kids Geo. "Convection" Kids Geo, 2010. <
http://www.kidsgeo.com/geography-for-kids/0064-convection.php>
"Physics for Kids: Heat Energy."
Ducksters. Technological Solutions, Inc. (TSI), 2014. <http://www.ducksters.com/science/heat.php>