Soon, I shall be visiting relatives in Florida. I have a history of doing science stuff with my niece. I thought the Dopers could give me some ideas on science experiments/demonstrations that are exciting, easy, and use components that can be found in the home or bought cheaply.
Assuming you haven’t shown them to her already, you could spend a bit of time playing with cornstarch and water, or putting things in red cabbage juice to test their acidity.
http://www.dangerousbookforboys.com/
and
http://www.daringbookforgirls.com/
I have the book for boys set aside for when my types are a little bit older.
I haven’t done cornstarch yet. I love the red cabbage idea, but need to know more about ph levels and such before I show it to her. I was actually going to post another thread asking for the acidity/alkalinity explanation of the color changing grape juice in my Special Effects Cookbook
ETA
I also need to know what causes hurricanes and tornadoes. She asked me today and I wasn’t sure.
Wikipedia has a decent explanation if you can follow it.
umm, couldn’t follow it.
I did the red cabbage thing for my website - here - I only ever intended it to be a bit of fun, but someone gave me the following review:
Well, Pantophage, I now know the answer to “Why does it change color?”
The answer is “It’s really complicated and involves molecular diagrams and words like quantized photon. You won’t understand it for a few more years.”
But, I would like an answer to “What is the difference between alkaline and acidic?”
Ancient Science is a great book! We had so much fun doing the experiments in this book. One note…if you make the sundial…make sure you correct for daylight savings time. It took us a while to figure out how we ended up exactly an hour off.
An acid has lots of hydrogen ion activity, with alkaline substances, it’s hydroxide ions.
Hydroxide as in hydrogen+oxygen as in water?
Or Hydrox like the cookies?
ETA
Looking at wikipedia I see hydroxide is HO. So H2O= harmless water but HO=dangerous base?
Well, just one hydrogen and one oxygen, compared to two and one for water.
So you could say it’s hungry for another hydrogen atom, whereas acids are trying to give them away.
Marvellous! That is exactly the kind of thing I was looking for when I started the thread.
BTW I do plan to impress on the kid the dangers of strong acids and bases. It’s a good chance to remind her that our stomach acid is dangerous but held at bay by a soapy layer of mucus.
We had a lot of fun producing hydrogen and then burning it. You get a glass bottle, mostly fill it with lye (aka Liquid Plumr), throw in a bunch of crumpled aluminum foil, put a balloon over the top of the bottle, and watch it fill with hydrogen over the next 10-15 minutes. Then tie the balloon to a stick and put a butane lighter under it. It gives you a nice pop, and as long as you do most of the work it’s quite safe. Our kids are 8 and 5.
That is also exactly the kind of thing I am looking for.
Here’s one I remember from my childhood (for reasons which I’ll go into later). It demonstrates how air under pressure can be used to push stuff around.
You’ll need:
– A soda bottle (2L will work well, though a smaller bottle will work also)
– A tight-fitting cap or cork for the soda bottle
– Chewing gum (you can use putty, I guess, but gum is more fun for a child)
– A straw
– Some water.
– A drill (to be used by the adult)
Have the adult drill a hole the same diameter as the straw in the cap or cork. Put the straw through the hole, and seal the straw in place with the chewing gum. You’re trying to make an airtight seal. Fill the bottle about two-thirds to three-quarters full of water, and screw the cap/cork/straw apparatus on the bottle tightly. Make sure the straw is under the water.
Now, you need to get the air pressure up in there. Blow in the straw–get some bubbles. Seal the straw with your tongue, and blow in again. Keep on doing this until you get tired of doing it, or until the water threatens to back up the straw.
Pull your face away fast. You get a fountain of water squirting straight up! The air under pressure pushed on the water in the bottle. Having no place else to go, the water went the only place it could: up the straw.
You can use this to explain such things as why aircraft in the movies that suffer a cabin puncture have not-secured objects flying around, or air braking systems such as are used in big trucks and trains. Or you can use it to explain wind: air under pressure pushes other air, and the result is wind. In short, air under pressure can be used to push things.
Now, why do I remember this from my childhood? Because the kid who demonstrated this science experiment to our class in elementary school didn’t pull his face away fast enough, and got a face full of water. Big yuks all around for our class of 10-year-olds! But the kid made his point about air pressure. Obviously, I never forgot it. 
Here is a simple home experiment showing how to promote verdigris on copper coins, and then as a bonus, using the solution to copper-plate steel nails after they’re done.
Have you thought about building a death ray?
Mousetrap car- we build our own, but here is an example
mentos and diet coke
I have also bought some old roman coins on Ebay (pretty cheap) and had the kids clean them off and try to find out how old they were.
My mother and sister have forbidden any Death Rays, or mind control experiments.