Stumping the Teacher: "Will it Float?"

[Nanabit]

This might sound like a stupid question, but in my physics class we have a game called "Will it float?" It's just like on the tonight show. We pick out random things to put in the water and guess if they'll float or not. My teacher decided to let us try to stump her after several weeks of her trying to stump us. If we get her, we get 5 bonus points! I've been trying to think of things that are guaranteed to stump her and have tried something, but to no avail. She's too good for us! Does anyone have any ideas on things that would almost definitely seem to float but then sink or vice versa??

 

[Njorl]

There are some oils that are denser than water. Most oils are lighter, and will float. I don't recall which are the dense ones, maybe you can do the searching. Also, present her with a selection of more dense and less dense ones. If you come in with just one oil, she'll know what's up.

Njorl

 

[HallsofIvy]

What is your teacher allowed to do? Just look at the object or lift it to estimate its density? If lift it, it's going to be hard to fool her- an oil might work: most people would guess "float" but you might be able to find one that will sink.

If your teacher is only allowed to look at it, you might try finding a large piece of pumice: volanic rock that has enough air bubbles to float. Most people would look at a rock and immediately decide it will sink.

 

[Nanabit]

Unfortunately, she is allowed to pick it up and touch it!

 

[arcnets]

There's a toy called a 'Cartesian Devil'. It's a little (1/2 inch high or so) hollow devil figure which has a hole so small that the water can't get in. If you put it in water, it floats. But if you put it in a plastic bottle filled with water, fasten the top, and squeeze the bottle, then the Devil sinks.

If you're not allowed to use a water bottle, you could use some plastic containers (e.g. film cans), and drill small holes into them. If the hole is big enough, then the water can get in and the can will sink. I think it's impossible to judge by eye whether the hole is big enough.

Well, I still think the idea with the oil is better.