Aug 2, 2012

Wingardium Leviosa: Levitating Water Science Trick

"Wingardium Leviosa" by Arieare on DeviantArt
Personal confession for the day: I am a serious fantasy and science fiction fan; in fact, I have what could be considered an "unhealthy" fascination with Harry Potter and his Wizarding World (admitting it is the first step to recovery). But I'm also super into science, which I think I've mentioned before. My job as a museum educator is so awesome, I can combine these passions for the fantastical and the empirical in cool ways to get kids interested in science and have a little fun with it. I really like putting together science magic demos and showing my art students how optical illusions work in the brain. When I was going through some of the demos we keep around in the museum for a special outreach event, I re-discovered this  very awesome water trick. I get geeky excited when I find a science experiment that demonstrates interesting real science AND looks like a wizarding spell from HP himself. I mean seriously, you can make water levitate, this is some real sciencey Wingardium Leviosa, baby. It's so simple and easy to put together, you can do it at home, right now, on a whimsical impulse if you want (those are the best kinds of science, BTW).
Here's my 4 minute video demo of the trick:

Suspended Water Trick

Things you'll need:
  • Mason jar with lid and ring
  • fine wire mesh
  • measuring cup with water
  • bowl
  • towel (for messiness)
Begin by constructing the meshy jar. Remove the ring and lid from the jar, pop out the flat lid and replace it with the wire mesh. Hold the mesh onto the open mouth of the jar and screw the ring onto the jar around it. The mesh should completely cover all of the mouth of the jar so that there are no gaps. Make sure the ring is screwed on very tightly. Now you can do the trick! Pour some of the water from the measuring cup into the jar through the mesh. Make sure to get a good amount of water in there so you can see the trick (I think it's best to fill up at least 2 - 3 inches from the bottom). Have the bowl ready close by. Hold the jar with one hand, and place the palm of your other hand over the mesh and the mouth of the jar. Try to cover as much of the mouth as possible, creating a tight seal (people with big hands might need to help those with little hands). Keeping the hand firmly over the mouth of the jar, very quickly flip the jar upside down over the bowl. Make sure the mesh and the mouth of the jar are perfectly (or as nearly as ) parallel to the ground - the jar must be level for the trick to work. Then, slowly and carefully (try to not touch any part of the mesh, or tip the jar) remove your hand from the mouth of the jar (now on the bottom). When you remove your hand, the water should stay suspended in the jar (maybe a couple of drops come out) as long as the jar is held level over the bowl. Tip the jar carefully to one side and all the water comes out!

Wait, what?

Like I say in the video, the water stays in the jar instead of spilling out like you might expect because of two reasons: water molecules are sticky to each other - cohesion - and that stickiness combined with air pressure pushing up on the water through the mesh keep it inside. Of course, the water is being pulled down by gravity and would naturally fall out of the mesh, but since each little cell in the mesh has its own surface tension - made up of the stickiness of the water molecules - each cell's surface tension is very strong in ratio to the size of the cell. Water always has surface tension. If you were to remove the mesh and just have the open mouth of the jar and then turn it upside down like in the demo, that water would still be cohesive and have a certain amount of surface tension, but that water would spill all over the place and would not stay suspended in the jar. The difference is the surface area of the water: tiny little holes in the mesh v. a big old mouth of the jar. The more surface area (the big mouth), the weaker the surface tension, meaning even the strong stickiness of the water molecules can't hold everything together with so much surface area. But with just a tiny bit of surface area and a great amount of tension in ratio to the surface area, keeping it all in by virtue of stickiness is no problem. Then there is pressure of air pushing up on the jar to help. Actually, to be more precise, there's air pressure everywhere squeezing everything in the environment - it's why bubbles and balloons are round, and why airplanes can fly. The air around the jar is pushing up through the mesh holes to help keep the water in (working together with surface tension, of course).  This is why the jar needs to be parallel with the ground when you take your hand away. By keeping it level, air pressure is evenly pushed up on the mesh so that each spot of surface tension is equally bolstered by the air pressure. The water rushes out when you tip the jar not beacuase you have changed the size of the surface tension for each spot in the mesh, but because you have changed how much pressure is pushing directly up on the mesh at different points, weakening some areas of tension. This is an experiment that is definitely worth trying, and it's one that can dazzle kids and adults. I recommend getting one of those little bitty mason jars and rigging up the top with some mesh to keep in a purse or backpack, for those frequent occasions you want to randomly show people science!

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