THINKING ABOUT ATMOSPHERIC PRESSURE
If you hold out your hand, how much air are you holding? How much does it weigh? You might think 'none' and 'nothing', because air doesn’t weigh anything. Or does it?
Actually, it does. Air is made of molecules like nitrogen, oxygen, water, and carbon dioxide.
Though tiny, these molecules do have weight, and they add up! The weight of air is called atmospheric pressure, or how many air molecules are in a specific area.
Have you ever climbed a mountain and became short of breath? That’s because the atmospheric pressure is lower up there, and therefore those life-giving air molecules are fewer and father between. There’s just not enough molecules to breathe in!
One of the things that can change atmospheric pressure is temperature. Wanna see how? Let’s do an experiment!WHAT YOU'LL NEED
You might want to label each bottle as 'hot' or 'cold' so you don't mix them up!
LET'S GET STARTED
What happened? Are they different?
So why did the hot water bottle crush itself?
The answer lies in what molecules do when they are cold or hot. Cold molecules tend to cluster together and not move very much. Hot molecules jump around and spread out.
Sort of like when you see penguins all huddled together, you know they're freezing! If you could crank up their heat, they’d spread out and have a big ole party.
Inside your cold bottle the molecules didn’t move much and didn’t need much space. They went from cold to cold, so the molecules didn’t change, and the pressure stayed the same.
However, your hot water bottle’s molecules were spreading out and bouncing off each other, so it started out with a high air pressure.
When you put it in the fridge, the cold made the molecules slow down and not exert as much force (or take up as much space).
This decreased the pressure and sucked the walls of the bottle inward!
MORE IDEAS FOR EXPERIMENTS
Try a similar experiment on your next airplane ride! Instead of testing temperature, test altitude. But instead of climbing a mountain, let a plane do the work!
Bring an empty bottle (with its lid screwed on tight) in your carry-on. What happens when your plane goes high up in the air? What happens when you land again?
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