How Does That Work: Doing the Back Float

This is a simple activity, but its explanatin is a bit sophisticated.  Therefore it's a good candidate for older and/or more advanced students.  But, don't let that stop you from trying it with younger students - keep your explanations basic and you might be surprised at what they take away from it.

What you'll need:

Baby oil

Water

Water bottle

Index card

Sharpened pencil

Hole punch

What to do:

Prepare a bottle, filled about half way with water and the remaining way with baby oil. 

On one side of an index card, color with a pencil, getting as much graphite as you can onto the index card.

Use a hole punch to punch the index card.

Place the hole punches into the bottle of oil and water.

What you'll see:
The dark side of the holes will always face the oil and not the water.  You can shake it up and they'll always return to that position.

Why:
Graphite is a good conductor, which gives it a negative polarity.  Water also has polarity, and it repels the graphite, so the graphite side will face the oil.


You can also talk about things like density, immiscibility and the like with this activity.

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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?