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MEASURING VOLUME OF LIQUIDS

Today we're going to learn how to measure liquids. The result of the measuring is called "volume."

The volume of a liquid can be measured by using any small container to fill a larger one, or, if you have a small amount to measure, by pouring into smaller containers until
you find one that exactly holds all the liquid. Each time a container is filled, that is one unit of measure.

Remember, a "unit" can be any size; it is called a "unit" because it is a "thing" all by itself. A thimble is a "unit" and a bathtub is a "unit." If you have three thimblefuls of
water, and the thimble is your "unit" of measure, you have "three units of measure" of the water. Same with the bathtub. It is important to say what the unit is - bathtub
or thimble - so the amount of liquid measures of it can be understood.

Mom, of course, has easy ways of measuring liquids. She can use a measuring cup or measuring spoon. The volume of liquid in containers used just for measuring (in our homes) is usually stated in terms of teaspoons, tablespoons, liquid ounces, cups, pints, quarts, half gallons, and gallons. But that is the easy way. One doesn't always have measuring utensils, and it is necessary to figure out another way.

We will begin by collecting some different kinds of containers that will hold liquids. We have paper cups, three sizes of drinking glasses, a thimble (just for fun), an empty
margarine tub, a kettle, a teacup, a coffee mug, a vase, and a few other containers. (We won't bother with the bathtub!) Let's arrange them in order of the amount of water we think they will hold; have the smallest container on the left, and the largest one on the right.

That lovely bud vase is much taller than the big drinking glass; let's put it to the right of the glass. Also, since some people use tea cups for coffee, and they are the same
height, they must be the same size; we'll put those next to each other.

We have a pail of blue water (colored with food coloring), which we can use for our experiment.

The first test will show us how good we are at estimating the volume of an amount of water. First, we'll fill the small drinking glass, all the way to the brim, with our blue water. Look at it closely, and decide how high the water would be if it were poured into some of the other containers. You could make lists; of containers that are the same type, number them "#1, #2, #3," according to their size, with the smallest one being "#1."

One of you thinks that the water would reach half-way to the top of the bud vase, because the bud vase is twice as tall as the glass. Whoops! The bud vase is full, even though I only poured out half the water from the glass! How can that be? Do you think it could be because the bud vase is skinny and the glass is fat? We will have to move the bud vase to a place in the line where we think it is close to the same size as a much smaller container.

This time we'll get a small container and estimate how many times we could fill it from the glass. The thimble would take too much time, so we'll try glass #1, which is the size used for serving juices. It's a lot shorter than the full glass (#3), and I heard somebody say we could fill it two times from the full glass.

Right! It is exactly one-half the size of the starting glass. We know that because we filled it once, poured it back into the pail, and filled it again.

This drinking glass is about the same height as the teacup and coffee mug. Somebody can try those. Usually, teacups are smaller than coffee mugs, so it would be best to pour the water into the teacup. Now, pour it from the teacup into the coffee mug. Oh, oh! The coffee mug is smaller. Do you suppose that is because it is so much thicker?

What we see from all this is that the size (in volume) of containers is sometimes hard to estimate; that we need to know arithmetic because we sometimes have to figure amounts of liquid; that we have to use our eyes in a critical manner and look at the different aspects of units, such as height, width, and thickness; that liquids have no shape of their own, but take on the shape of their containers; and that containers used for measuring are really handy!

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