Making a Density Column

This experiment is one of the classics that is still a lot of fun to play with. It has to do with density. Density can be a difficult concept to grasp, but it is much easier once you have played with a density column.

Imagine that I have three cups that are the same size. If I fill one cup with water, one with sand, and one with lead. Would they all weigh the same? No, of course not. A cup of sand weighs more than a cup of water. Sand is denser than water. Lead is denser than sand, so a cup of lead weighs more than a cup of sand.

Floating Bubbles

This time we are going to produce some floating bubbles. Instead of filling the bubbles with hydrogen or helium, our bubbles will be filled with ordinary air, and will be floating on a layer of a heavier gas.


Bowl of water on scale
I weighed this bowl of water. If I stick my hand in the water, and weigh it again, will it weigh more? If so, how much more. If not, why not?


Ice in bird bath
We are expecting a hard freeze tonight. The water in our bird baths will probably have a layer of ice, if they don't freeze solid. If cold water sinks, why does the ice form at the top?


Sandstone cliff
As winter approaches here in Johnson Canyon, I will be paying close attention to katabatic winds. Without looking it up, what are katabatic winds, and why would they be important to us in the canyon?


plastic bag on scale
I weighed this plastic, storage bag while it was empty. Then I opened it to fill it with air. Sealing the bag again, I put it back on the scale. Was its weight the same, more, or less? Why?


Balloon on scales
A plastic, storage bag would not weigh more when it when it was filled with air, but when I blew up this balloon, its weight did increase. Why?