Friday, November 19, 2010

How Does That Work: Magic Marble

A "marble" that hovers right in the middle of the cup.  Can your students explain it? 
{It's all about density and immiscibility}

Fill a cup between 1/3 and 1/2 full of water.  Add a drop of two of food coloring.

Use a dropper to place a couple of blobs of cooking oil on the water.

Tilt the cup and pour in rubbing alcohol.  (You want to pour the alcohol down the side of the cup, so you don't mix the water and alcohol and also so you don't disturb your oil blobs).

Add a drop or two of food coloring to the top of the cup, if needed.

[If you wish for something a bit more permanent, create your magic marble in a jar and cover with the lid.  

To keep your "marble" hovering in the liquid, don't shake or disturb the cup.  If you're curious what happens if the alcohol and water are mixed, make a hypothesis and have at it!

How Does That Work is a series of products and demonstrations that you can present to your students and challenge them to explain the science of how they work. Make sure you decide ahead of time what you'll accept as a valid explanation - can it be printed straight off the internet, written in the student's own words, or does the student need to be able to explain it to you conversationally? What will a valid explanation earn the student - a prize, extra credit, a feeling of goodness?

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