Don't Be Dense!

Before we start experimenting with flotation, let's have a few words about density, because it will be very important in the upcoming posts. Talking about density always reminds Dr. B of a silly riddle: "Which weighs more, a pound of iron, or a pound of feathers?" Most people say, "Of course, iron is heavier, so a pound of iron weighs more!"

But think about this carefully - a pound is a measuret of weight, so a pound of iron and a pound of feathers weigh exactly the same. Now, a pound of iron is certainly smaller than a pound of feathers , but the weight is identical. When we use the word "heavy", we often really mean that something has a high density. Density is the weight of an object divided by its volume (size). One cubic foot of iron (a cubical box with each side a 1-foot square) weighs almost 500 pounds, so its density is about 500 pounds/cubic foot (abbreviated as cu ft). Two cubic feet of styrofoam weighs just about 4 pounds, so its density is 4 pounds/2 cu ft, or 2 pounds/cu ft. What is the density of water, if 4 cu ft weighs 250 pounds? Check back in a few days for the answer and for the first experiment on floating.