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FYI: You can also do this with a simple bucket (you don't need the skinny container), but then you have to look down into it to see the parabola. Interesting variants on this include putting a small plastic boat (of a fishing floater) in it and asking the question: where will it go - to the outside or inside? Or…putting a sinker in it and asking where that will go. Or putting sinker attached to a floater in it….
this takes the idea and shifts it into an inquiry question.
To go further, you can put some light objects that barely sink in a bucket of water. Ask what will happen to the objects when you either rotate the tub around its center or simply stir it with a large spoon. Then try rotating the tub around or stirring it using a large spoon. Those who have brewed loose leaf tea may be familiar with this effect (and it is an exhibit - or used to be at the Exploratorium).
I would caution against explaining the parabolic arch of water by saying it demonstrates Centripetal force though. Centripetal force is literally the force of the sides of the pail pressing inwards on the water - this doesn't seem to explain the parabolic arch of the water. It might be better to say that it is a Centrifugal effect - and how centrifuges work. Or, you can say that this is one proposed method of generating artificial gravity in a space station in outer space. Or you can talk about inertia, and how once something is moving, it wants to keep moving IN a STRAIGHT LINE. So once you swing something around to one side, it wants to keep going to that side - but the side of the container is there, so it piles up against the side of the container. The faster you move it, the more you're throwing it outwards, so the flatter it is agains the side of the container (and the less liquid there is in the center).
Meanwhile if you want to get the idea of centripetal force (literally a center seeking force), then do the following:
Tie a foam ball to a string (the hard but safe way), or tie some washers to a string (the easier but more dangerous method).
Thread the string through a straw. Hold onto the end of the string that went through the straw with one hand and the straw with another hand, and start swinging it around overhead. Notice that the faster you swing the washers/ball, the more force on your hand holding the string - your hand is providing the centripetal force that keeps the washers/ball swinging around the straw. if you let go, the ball/ washers go off in a straight (tangential) line.
Poor diagram:
___________STRING_________________Washers or Ball
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| Straw with string going through it
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Hand holding other end of string.
One other thing you might do is go to howtosmile.org and search terms such as: "spin" "rotation", "centrifugal" "centrifuge" "centripetal." It's a pretty good resource for activities.
Hope some of that helps!
-William
On Jul 23, 2013, at 12:22 PM, Beth Demke <[log in to unmask]> wrote:
> ISEN-ASTC-L is a service of the Association of Science-Technology Centers
> Incorporated, a worldwide network of science museums and related institutions.
> *****************************************************************************
>
> We have a spinning water exhibit that would be easy to replicate for a family event. Find a clear skinny container that can hold water. (The container on our exhibit has the following measurements: 12" high x 12" wide x 2" wide.) Fill approximately 1/3 full of water colored with a bit of food coloring. Center container on a lazy susan and spin. The spinning motion will create a parabola, demonstrating centripetal force.
>
> Beth Demke
> Executive Director
> Gateway to Science
> 1810 Schafer Street, Suite 1
> Bismarck, ND 58501-1218
> 701.258.1975 (office)
> 701.220.8356 (cell)
> [log in to unmask]
> http://gatewaytoscience.org
> "Knowing a great deal is not the same as being smart; intelligence is not information alone but also judgment, the manner in which information is collected and used"
> Carl Sagan (1934-1996), American astronomer, exobiologist and science communicator
>
> -----Original Message-----
> From: Informal Science Education Network [mailto:[log in to unmask]] On Behalf Of Daniels, Alissa
> Sent: Tuesday, July 23, 2013 11:45 AM
> To: [log in to unmask]
> Subject: Re: spin experiments
>
> ISEN-ASTC-L is a service of the Association of Science-Technology Centers Incorporated, a worldwide network of science museums and related institutions.
> *****************************************************************************
>
> take a bucket of water and swing it around over your head. Oooooooo!!!
> (I have a bunch of yogurt cups with handles of cotton twine, so kids can try it too without too much worry about spilling tons of water. That said, I still do this outside...)
>
> AD
>
>
> -----Original Message-----
> From: Informal Science Education Network [mailto:[log in to unmask]] On Behalf Of Allison Feigen
> Sent: Tuesday, July 23, 2013 12:26 PM
> To: [log in to unmask]
> Subject: spin experiments
>
> ISEN-ASTC-L is a service of the Association of Science-Technology Centers Incorporated, a worldwide network of science museums and related institutions.
> *****************************************************************************
>
> Hello,
>
> I'm looking for some simple, low mess experiments I can do at a family program that demonstrate the properties of spinning. I'm planning to do salad spinner spin art; I tried steve spangler's chromotography experiment with little success. Does anyone have any suggestions?
>
> Thanks!
> ~Alli Feigen
> Education Manager
> The New England Carousel Museum
>
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