Popcorn Science

This week we did a little popcorn science, the questions being: what happens to the mass and volume of popcorn after you pop it and why does heating kernels make them pop? 

We measured the mass and volume of a sample of kernels and then threw in some oil (30 ml / 23 g to be exact). We put all the popcorn into a pot with said oil, turned on the stove, waited, and then POP! We took out the popcorn, weighed it, measured the volume, and here's what the kids concluded: The kids predicted the volume would increase and so it did...practically by a factor of 10. The mass, on the other hand decreased a tiny bit. 

As for why the heat makes it pop...turns out there's a tiny bit of water inside each kernel, which when heated expands and exerts enough pressure to burst the kernel open. As each kernel "explodes", its volume increases while at the same time allowing a small amount of water to escape, accounting for the slight decrease in mass.

Measuring the Volume of Stuff That's Shaped Kinda Weird

We learned a new use for graduated cylinders. Turns out they're not just good for measuring the volume of liquids, but used cleverly can help us measure the volume of objects that are shaped kinda weird. When it comes to simple shapes, like a block, you can use a ruler to measure the different dimensions, but with something like a screw or a paper clip, how do you figure out EXACTLY how much space it takes up? Here's a clue: What happens to the water level when you get into the bath and why?

Measuring Mass

This week we added the triple-beam-balance to our repertoire of measuring tools. First we discussed the difference between volume and mass, and then we worked in pairs guessing and weighing different objects. Finally we checked ourselves and the triple beam balances using a digital scale. We noticed that a) we measured pretty consistently, and that b) our triple beam balance was only off by about a toothpick. Not that big a deal, unless of course, you're measuring toothpicks!

So what do you think weighs more...a pound of gold or a pound of feathers?

Biology: Why are cells so small?

I've been getting some push back from the kids on all the tiny stuff we've been studying: microscopes, cells, chemistry, etc. So before we move on to bigger and better things, I thought we should at least address one last itsy bitsy, but not unimportant question: Why are cells so darn small? Even elephants, whales, and oak trees, big as they are, are made of of tiny cells, the same size as the unicellular organisms we found in drops of pond water.

To answer this question we looked at potatoes. The potatoes represented cells, and we submerged these potato cells in iodine, which stood for oxygen, food, waste or whatever stuff needed to be moved in or out of the cell. We cut up potatoes into 2 different-sized cubes: teeny tiny (c. 0.5 cm3) and large (c. 5 cm3). We placed these in a jar of iodine and waited. After about 20 minutes, we removed the potatoes, now black after reacting with the iodine, and sliced them in half. The idea was to see how far the iodine penetrated the potato (Picture shows similar experiment done with agar cubes absorbing phenolphthalein). In both teeny tiny and large potatoes the iodine moved less than a millimeter in. However, the big difference was when we considered what percentage of the potato had been exposed to the iodine.

We discussed how the surface area of cell is a limit on how much stuff can be moved in and out of a cell, while the volume of the cell determines the demand on imports (food, O2, etc) and exports (waste products). In large cells, there is simply too much volume for the surface area to handle, and the cell cannot move stuff in and out of the cell fast enough to meet the cell's needs.