What Is Dry Ice and Why Does It Make Fog?

It looks like magic. It makes spooky fog that pours down instead of floating up. And it never leaves a puddle. So what is dry ice actually doing?

Dr Matt Agnew unpacks the weird science of dry ice, what sublimation is, why the fog pours downward like a waterfall, and why dry ice behaves so completely differently from the ice in your freezer.

What you'll learn:

Normal ice is frozen water... dry ice is frozen carbon dioxide, the gas we breathe outDry ice skips the liquid step entirely... straight from solid to gas with no puddleScientists call that process sublimation, one of the most interesting phase changes in scienceThe fog is mostly not carbon dioxide at all... it's water vapour from the surrounding air getting chilled so fast it becomes visibleCold air and carbon dioxide are both heavier than regular warm air, so the fog pours downward like a fog waterfallDry ice is essentially a natural fog machine used in theatres, film sets and Halloween displays worldwide

Key Science Ideas:

Sublimation: When a solid skips the liquid stage and goes straight to gasCarbon dioxide: The gas we breathe out, and what dry ice is made ofWater vapour: Invisible water in the air that becomes visible when it gets suddenly coldPhase change: When matter moves between solid, liquid and gas statesDensity: Why cold air and carbon dioxide both sink rather than rise

Safety note: Dry ice is extremely cold and must only be handled by adults wearing insulated gloves. It should only be used in well ventilated spaces. This is a watch and learn episode.

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