Which way is up?

Simple questions sometimes have subtle answers.  Of course, some answers are also pretty simple.  Which way is up starts out simple and then gets pretty subtle. (Note on scientist-speak: subtle = complicated and/or difficult).  This winds up being related to What is a day? as we get a little more complex.  But, while we can, let's go with simple.  Up is the opposite of down.  Slightly less simple, down is the direction a ball falls.

Even less simple: hang a weight on a string.  Hold it still.  This is difficult, so maybe hang it from a nail or off a board.  There's probably still a little swinging back and forth.  So either wait (it'll come to a halt eventually, but who says scientists are always patient?!) or get a large (larger than your weight) cup or bucket of water and bring that up underneath the weight.  Make sure the weight is made of something that doesn't float if you use this approach!  Once the weight comes to a halt, the string gives you a line which points up and down.  The weight is the 'down' side of the line.

By the way -- not only do you not have to be good at math to be good at science, you also don't have to be good at drawing. For me, this is pretty good artwork. Some people are great at drawing, same as some are great at math. Some of us, well, you see my caliber of artwork.

 Now for getting subtle ... which also explains why the earth isn't exactly a sphere.

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Kitchen experiments

Some simple, if possibly messy, fun.  Ingredients: Water and corn starch, baking powder and vinegar.

The baking powder and vinegar mix to release carbon dioxide gas.  If you put it inside something with a tight cap that can blow off, you've got a 'rocket'.  Just be sure to aim it away.  I don't really remember well, but I think equal vinegar and baking powder is the right recipe.  But it's something to experiment with.

Corn starch and water is a chance to explore the mechanical properties of matter.  (read: mess around while claiming to be doing science)  Ordinary fluids, like air or water, react straightforwardly to pushing on them.  If you push, they move out of the way.  Push harder, they move out of the way faster.  Corn starch and water (again, I think it's equal amounts, but experiment) are a different kind of thing.  Set a marble on top of the mixture and it will sink through.  Throw the marble at it, and it will bounce. !?  Experiment.  It makes a difference how fast you push.  Lots of room for experimentation.

Anyone else have comparably simple experiments?

Designing good experiments

This is another time I don't really have great answers, but a question over at the question place has me thinking about it.  Namely, what makes for a good experiment?  As far as the science goes, I'm comfortable about knowing the answer.  Or at least knowing enough of an answer. 

But for the purposes of you readers -- what makes for a good experiment that you could do yourself?  How big or small could it be?  How long should it take to run?  How much expense is ok?  Is following a circuit diagram to assemble test equipment something you're comfortable with?  Carpentry?   And so on. 

For the original question -- a tabletop demonstration of the greenhouse effect -- I might actually have an answer of sorts.  I went running shortly after first reading the question.  That's often a good time for ideas to come to me, and a few did.  But at the moment, they'd take a pretty big table (like, say, 10 feet), you'd have to get hold of a dry ice supply (for the CO2), and you'd have to assemble a fairly simple circuit.  A several Watt laser would also be a plus, but I'm going to try to make sure that the experiment will work without it.