Sorting All Sorts of Trash

In some communities, people must separate their recyclable materials into different categories, such as glass (clear or colored), paper, cardboard, aluminum, plastic, etc. Other communities use single-stream recycling, in which everything is put into one large container; sorting occurs later.

If you watched the recycling center videos, you saw that they use some pretty cool methods for separating trash into different types. Sometimes, it's very simple, with a trained sorter picking items out by hand. Other separation methods use magnets or flotation. In this experiment, you will investigate different items that might be in the trash, and will try to figure out ways to separate them all.

What You'll Need:
Pieces of different plastics about 1 inch (2.5 cm) square (find plastics with different numbered recycling codes to ensure that they're different)
Aluminum foil (1 inch or 2.5 cm pieces)
Aluminum can
Steel can
Newspaper (1 inch or 2.5 cm pieces)
Copier paper (1 inch or 2.5 cm pieces)
Magnet
Knitted wool or acrylic item (like a hat or mitten)
Hair dryer
Large bowl
Water

1. Place the magnet near all the different kinds of trash you've collected. Which kinds are attracted to the magnet? Could you use a magnet to remove these from the recycling stream?
2. Rub the knitted item on your hair to give it a static charge. Are any of the trash items attracted to the charged knitwear?
3. Place all of the pieces of trash on a table and aim the blow dryer at them. Turn the dryer on. Which types of trash get blown about, and which ones stay put.
3. Fill the bowl with water and place all of the pieces of trash in the water, one at a time. Which ones float, and which ones sink?
4. Using what you have found, can you figure out a series of sorting techniques that will let you separate all of your trash into different categories? You can use techniques more than once if that helps. If you can't, which things are hardest to separate?

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.