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Wow we learned a lot from Dr. Chambers. I wrote this for my trip. Don't forget to

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add water vapor and condensation. I know that's a clue because it's how rain is

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made. Hi where's Dr. D? Is he here today? We haven't seen him yet. Hi guys I'm here.

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You have that look like you're working on something. We're concerned about

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missing our physics fair because of the storm. We don't want to miss riding those

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roller coasters. Can you give us some clues on how to understand the weather?

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Sure. Something you definitely need to understand is energy. There's an electric

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motor that provides the energy to raise a roller coaster car to the top of the

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first hill and then gravity takes over. What energy source makes the weather

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happen? Do you mean what makes the winds blow? Or what raises the rain into the

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clouds just like the roller coaster was lifted? Exactly. I don't know. I think you

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do. It's the same energy source that makes the plants grow. Oh the Sun I knew

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that. When the Sun heats the earth, some areas become hotter than others. This is

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uneven heating that produces the winds. Wind? It can make wind? Air always moves

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from a region of higher pressure to a region of lower pressure. Wait Dr. D we

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haven't learned about pressure yet. What's that? I guess I better slow down a little

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bit. Air is made up of molecules like oxygen and nitrogen. They're constantly in motion

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traveling in straight lines until they bounce off of something. So you mean right

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now we're being bombarded with molecules? That's right.

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Molecules bounce off of something and they apply a force to that object. This force

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creates what we call air pressure. Let me show you an example. These hemispheres have

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molecules bouncing off the outside. I've taken most of the air out of the middle

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so there are very few molecules on the inside pushing out. Here try to pull it

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apart. Wow this is really hard. That force you talked about is very real. Now if I

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let the air back into the middle we'll have molecules both pushing out and

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pushing in. The pressure on the outside is the same as the pressure on the inside. It

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shouldn't be a problem. It's much easier now. Let's try something else. Put on your

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goggles and safety glasses.

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I'm gonna heat the air inside this can. There's a little bit of water in it.

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I'm gonna turn the can upside down into the pan of water and the pressure in the

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can is gonna drop very very quickly and the higher pressure air on the outside is

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gonna crush the can.

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Watch this. That's amazing. Now when I blow up this balloon I'll be increasing the

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density of the air inside. That means the molecules will be more tightly packed.

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This makes the pressure on the inside greater than the pressure on the outside.

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I knew that was going to happen. So that's what you meant when you said the

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air went from a region of higher pressure like the balloon to a region of

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lower pressure like this room. Very good. Now suppose you're at the beach in the

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summer. The sand is hot and it warms the air above it. Now warmer air has a lower

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pressure than cooler air because it's less dense. Now the air above the ocean

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is cooler therefore it has a higher pressure than air above the sand. What

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happens? Well I would think just like the balloon that the wind will blow from the

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higher pressure air across the ocean toward the lower pressure air on the

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beach. Very good. That's what's called a sea breeze.

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There's an update from the Weather Channel. The problem that we reported earlier has slightly strengthened and

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become more organized with maximum sustained wind now at 30 miles per hour.

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This system has been upgraded to a tropical depression. It is currently

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located at 15 degrees north and 40 degrees west and it is moving northwest

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at 20 miles per hour. Here's a globe. Look here are the Antilles Islands. I think we

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should start tracking the storm. Don't you? Oh I don't think so. It's far away. We

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don't need to worry about it. Yes we do. The storm has turned into a tropical

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depression. I don't want to miss the physics fair or our trip to Florida.