Main->Readings->4th Grade Readings->Matter->Part 1: The Stuff That Makes Things
Vocabulary |
Look at your hand. Stand on the floor. Drink a glass of water. Breathe in some air. All the time, every day, we are surrounded by things made of something we call "matter." The whole universe is made of matter. But what is matter? People wondered about that for centuries.
These days, scientists know matter is made of atoms. Atoms are the smallest particle of matter. Atoms are so small you cannot see them. They are so small you cannot see them with a microscope. They are so small that light rays miss them. In fact, until the later part of the 20th century, though scientists knew they must exist, nobody had ever taken a picture of an atom.
How could scientists guess it existed if they had never seen it? They made a kind of careful guess called a hypothesis (hy-POH-thuh-siss). Then they tested their hypotheses with experiments which could prove if their guesses were wrong or not. Scientists had a theory that something like the atom must exist, and every test they did proved they were not wrong. It turns out that atoms are very small and very odd. They are made of energy, and they are always moving.
Matter is everywhere, but is not the only thing in the universe that is made of energy. Examples of energy include the light from the sun, the signals that come to your television, and the electricity running through the wires. What makes matter different? We say matter is different from energy because it takes up space and has mass, and that is the definition scientists use.
What does "takes up space" mean? Well, let's use you as an example. You are made of matter. Can you and another student be in exactly the same place at the same time? You could be very close, but you could not be in exactly the same place. That is because you both take up space.
Another example is a bath. When you step into the water, the water level rises. Water is matter, and takes up space. So do you. Therefore, when you step in, you push the water out of the way and it must go up.
If you fill a box with tennis balls, it will only take a certain number of balls before you cannot close the lid any more. If you pour water into a bucket, the bucket can only hold a certain amount of water. These are examples of matter taking up space.
Whenever you say something is "big" or "small," you are talking about space. Volume is the word scientists use for the amount of space matter takes up. As you can guess from the word "amount," you can measure volume. There are many ways to measure volume.
You can measure the volume of something by measuring its sides and using arithmetic to figure out how much space it takes up. This only works well for things with very regular sides, like cubes, blocks, pyramids, and spheres. It is great for measuring the volume of something like a shoebox or a room, though.
Here is how you would measure a shoebox. With a ruler, measure its length, its width, and its height. Write your numbers down. Then multiply the length times the width. Multiply that times the height. The number you get is the volume of the box.
If you have something which is liquid or powdery, it is even easier to measure its volume. You can take a container which is marked with units of measure. When you cook, you use a measuring cup. Scientists use measuring cups, too, but they call them graduates, and they are marked very accurately. With this kind of container, all you do is pour in the thing you are trying to measure, and write down how far up it goes.
But suppose you have an object which is not liquid, not powder, and not a regular shape like a cube or a sphere. How could you measure its volume? Let's go back to that bathtub. Remember when you get in, the water level rises. How much does it rise? Exactly as much as your volume. You take up space, and water takes up space. When you get into the tub, you push exactly the same amount of water out of the way.
You can do the same thing with other objects that have an irregular shape. If you have a graduate partly filled with water, you can notice how much water there is. Then you can drop the object you wish to measure (let's say it is a rock) into the water. Just as in your bathtub, the water will rise. How much does it rise? The same amount as the volume of your rock. We call this method displacement of water.
Measuring volume by displacement of water.
So these are the three ways you can measure volume:
A bowling ball and a basketball take up the same amount of space. They have the same volume. There is a big difference, though, isn't there? If you dropped a basketball on your foot, you would prbably not be hopping around saying "Ow!" The same is not true for the bowling ball.
The difference between a bowling ball and a basketball is not volume. It is mass. Mass is the word scientists use for the amount of matter in something. And guess what? You can measure mass, too.
If you have ever sat on a seesaw, or balanced the center of a ruler on the tip of your finger, you know that the heavier side goes down and the lighter side goes up. If both sides are exactly equal, the seesaw or the ruler is perfectly level. Scientists use this fact to help them measure mass.
Scientists use a balance to measure mass. There are many kinds of balance, but they all work the same way. On one end of the balance, you put the thing whose mass you want to measure. On the other end, you put objects whose mass you already know. When the sides are perfectly balanced, you know you have exactly the same amount on each end, and you know the mass of your object.
Wait a minute! Aren't we just talking about weight here? Why can't you use a bathroom scale to measure mass? Well, there is a difference between weight and mass, and it is one that might not occur to you.
Weight is the measure of how hard gravity is pulling on you. On Earth, on the ground, gravity is pulling on you a certain amount (say, 75 pounds). A bathroom scale has a spring in it, and the amount the spring gets squeezed shows your weight. But if you were on Mars, where the gravity is less, you would not weigh as much. Does that mean you somehow lost some of your matter? No, your mass would be the same. On a balance, you would still have the same mass. Also, though you might not realize it, your weight changes when you go up or down in an elevator because of how you are moving. So scientists do not measure mass with a spring scale.
In the next section, we will talk about the measuring systems scientists use.
Questions: For your first assignment of the week, answer these questions in complete sentences on a sheet of loose-leaf paper, with a proper header:
Notes: For your second assignment of the week, in your journal on the next clean page, write the vocabulary words from this section and their definitions.
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Go on to Part 2: Measuring Matter
This page last modified August 15, 2002
Copyright ©2000 Delia Marshall Turner. All rights reserved.
Questions? Send me a note at dturner@haverford.org