# Static Electric Spark from Cup of Soda? **URL:** \ **Category:** Factual Questions\ **Created:** [May 18, 2015, 3:09am UTC](https://boards.straightdope.com/t/static-electric-spark-from-cup-of-soda/720281 "2015-05-18T03:09:56Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![Trinopus](https://avatars.discourse-cdn.com/v4/letter/t/2bfe46/32.png) [@Trinopus](https://boards.straightdope.com/u/Trinopus)\ **Post date:** [May 18, 2015, 3:09am UTC](https://boards.straightdope.com/t/static-electric-spark-from-cup-of-soda/720281/1 "2015-05-18T03:09:56Z")
It seems to me to happen all the time: I’ll buy a soda at a fast food place, where the cup is made of plastic. I’ll fill it with soda at a fountain. I’ll start to sip…and get a tiny little zap on my lip. Is this just a static electric spark, same as you get when shuffling across a carpet and touching a doorknob? Is the electricity accumulated from the carbonated water running through the nozzle? Have I just re-discovered the Leyden Jar? At first, I thought it was a chemical thing, perhaps the salt on my lip popping a CO2 bubble. But it seems always to happen only with the first sip, so static electricity is now my leading guess. ---
**Author:** ![Baracus](https://avatars.discourse-cdn.com/v4/letter/b/2bfe46/32.png) [@Baracus](https://boards.straightdope.com/u/Baracus)\ **Post date:** [May 18, 2015, 3:19am UTC](https://boards.straightdope.com/t/static-electric-spark-from-cup-of-soda/720281/2 "2015-05-18T03:19:12Z")
Unless you were wearing gloves, any potential difference between you and the cup should have been resolved before you took a sip. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [May 18, 2015, 3:55am UTC](https://boards.straightdope.com/t/static-electric-spark-from-cup-of-soda/720281/3 "2015-05-18T03:55:20Z")
> [@Baracus](#): > > Unless you were wearing gloves, any potential difference between you and the cup should have been resolved before you took a sip. Well, that’s interesting. Foam cups are very good insulators. If you generated a static charge by walking across the floor, and then filled the cup without touching the dispenser with your hand, I could see how the liquid in the cup might be charged relative to your body, and give a small shock. ---
**Author:** ![Trinopus](https://avatars.discourse-cdn.com/v4/letter/t/2bfe46/32.png) [@Trinopus](https://boards.straightdope.com/u/Trinopus)\ **Post date:** [May 18, 2015, 4:21am UTC](https://boards.straightdope.com/t/static-electric-spark-from-cup-of-soda/720281/4 "2015-05-18T04:21:00Z")
> [@Baracus](#): > > Unless you were wearing gloves, any potential difference between you and the cup should have been resolved before you took a sip. Not the cup, but the liquid in the cup. The cup is a non-conductor, ordinary cheap plastic. The spark happens when the liquid first touches my lip. ---
**Author:** ![marking](https://avatars.discourse-cdn.com/v4/letter/m/4da419/32.png) [@marking](https://boards.straightdope.com/u/marking)\ **Post date:** [May 18, 2015, 11:50pm UTC](https://boards.straightdope.com/t/static-electric-spark-from-cup-of-soda/720281/5 "2015-05-18T23:50:13Z")
I have noticed this too. No real answer, but… I occasionally have McDonalds for lunch, but for health reasons (ha!), get an apple juice and a cup for water. I get a tiny shock the instant the water contacts my lip, so I’ve eliminated the possibility that it has anything to do with carbonation. ---
**Author:** ![Trinopus](https://avatars.discourse-cdn.com/v4/letter/t/2bfe46/32.png) [@Trinopus](https://boards.straightdope.com/u/Trinopus)\ **Post date:** [May 19, 2015, 1:19am UTC](https://boards.straightdope.com/t/static-electric-spark-from-cup-of-soda/720281/6 "2015-05-19T01:19:09Z")
Does water acquire an electric charge from flowing through a nozzle? Sort of like brushing a comb with a piece of silk? I’ve also heard that helicopter rotors generate static charge. Is it something to do with the continuous motion? (We can generate all the power we need…by petting a fifty-foot kitty-cat, or getting Paul Bunyan to shuffle his feet over a nylon carpet!) ---
**Author:** ![TANKSPUd](https://avatars.discourse-cdn.com/v4/letter/t/58956e/32.png) [@TANKSPUd](https://boards.straightdope.com/u/TANKSPUd)\ **Post date:** [October 14, 2022, 2:24pm UTC](https://boards.straightdope.com/t/static-electric-spark-from-cup-of-soda/720281/7 "2022-10-14T14:24:34Z")
I’m searching for the same answer! Every time I get a Wendy’s lemonade (plastic cup and paper straw) it shocks me when I go to put my lips to the straw?!?! ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [October 14, 2022, 5:36pm UTC](https://boards.straightdope.com/t/static-electric-spark-from-cup-of-soda/720281/8 "2022-10-14T17:36:08Z")
Welcome, TANKSPUd! And thank you for bringing one of our dead threads back to life. I think water probably acquires charge rushing through the nozzle. There are lots of flow situations that transfer charge, from lightning clouds on down. There’s an interesting high voltage generator made from two metal cups, each coming to a point with a fine hole at the bottom, like funnels except so tight the water just drips. And, each cup has a metal arm reaching over to a ring positioned below and around the outlet of the other cup. Randomly one will have higher potential than the other. As a result, continued dripping keeps concentrating charge on the forming drops, drawn there by the ring connected to the opposite cup. The two cups wind up with big positive and negative voltages. ---
**Author:** ![jnglmassiv](https://avatars.discourse-cdn.com/v4/letter/j/f07891/32.png) [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)\ **Post date:** [October 14, 2022, 9:20pm UTC](https://boards.straightdope.com/t/static-electric-spark-from-cup-of-soda/720281/9 "2022-10-14T21:20:08Z")
> [@Napier](#): > > There’s an interesting high voltage generator made from two metal cups … I couldn’t visualize it, turns out it’s called a Kelvin water dropper. > **[Kelvin water dropper](https://en.wikipedia.org/wiki/Kelvin_water_dropper)** > > The Kelvin water dropper, invented by Scottish scientist William Thomson (Lord Kelvin) in 1867, is a type of electrostatic generator. Kelvin referred to the device as his water-dropping condenser. The apparatus is variously called the Kelvin hydroelectric generator, the Kelvin electrostatic generator, or Lord Kelvin's thunderstorm. The device uses falling water to generate voltage differences by electrostatic induction occurring between interconnected, oppositely charged systems. This eventua A ... ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [October 18, 2022, 5:58pm UTC](https://boards.straightdope.com/t/static-electric-spark-from-cup-of-soda/720281/10 "2022-10-18T17:58:09Z")
> [@jnglmassiv](#): > > I couldn’t visualize it, turns out it’s called a Kelvin water dropper. That’s it! Though I think there are different possible configurations, and the one in this illustration is a little different than what I described. The illustration shows a single water source feeding two droppers, which clearly constrains the droppers to have the same potential, and they get voltage between two receivers. I was describing a version with two insulated water sources, which exhibit the potentials. Still, it’s the same basic idea, in which those rings are what cause charge to concentrate on the droplets as they form.