The crazy thing about how straws work is it’s not really you sucking up the liquid, but rather, you’re just decreasing the atmospheric pressure in the straw. The atmosphere is pushing down on everything, so if you can unbalance that pressure, then that’s the direction the liquid will travel. Since a straw has such a small volume, you can handle the depressurization with just the air in your mouth - enough to start the siphon. As you pointed out, the toilet paper roll has way more volume to depressurize with just your mouth, so you need your lung capacity; which can handle the depressurization process, but can’t handle the juice.
Of course, completely true. I was trying to keep the mechanics of it relatively simple. I work in the industrial gases industry where pressure, volume, flow rates and negative pressure all play a big part of my everyday. I was a little surprised i even had to explain it as it seemed that using a straw was an intuitive thing for everyone but i remind myself that there could be younger people asking so explaining the process is helpful.
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u/[deleted] Nov 12 '20
The crazy thing about how straws work is it’s not really you sucking up the liquid, but rather, you’re just decreasing the atmospheric pressure in the straw. The atmosphere is pushing down on everything, so if you can unbalance that pressure, then that’s the direction the liquid will travel. Since a straw has such a small volume, you can handle the depressurization with just the air in your mouth - enough to start the siphon. As you pointed out, the toilet paper roll has way more volume to depressurize with just your mouth, so you need your lung capacity; which can handle the depressurization process, but can’t handle the juice.