At a birthday party in Phoenix, mom and dad begin inflating the balloons with helium. They both notice that the tank begins to cool down as they are inflating the balloon. Why?

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Well , as the helium flows from tank to balloons , the helium inside the tank decreases , so air fills the remaining space inside the tank. Also , helium is stored under high pressure in the tank because , helium is lighter than air , so its molecules have high energy and this energy causes pressure which increases the temperature. Once the helium is let out , the tank cools down.

Thank you

they it depends on if one believes about radioactivity, they make a geiger counter beep but maybe it was going to beep anyway electronics do wierd things all the time or it was programmed to beep near certain metals.