Use graphs to identify patterns showing weight remains the same

Imagine you tear a piece of paper into tiny bits. It looks very different now! But did any paper disappear? Scientists asked this same kind of question hundreds of years ago. They wanted to know if matter (the stuff that makes up everything around us) could ever just vanish.

For a long time, people thought that burning wood destroyed the material. They saw flames, smoke, and ash — and assumed some matter was gone forever. It took careful experiments and accurate scales to find the truth.

Here is the big question we will investigate: When we change what matter looks like, does its weight change too? Graphs will help us find the answer!

Before we look at graphs, we need to understand a few key ideas. These ideas come from the NGSS Disciplinary Core Idea that the total weight of matter is conserved (stays the same) when it changes form. We also practice the Science and Engineering Practice of analyzing data. The Crosscutting Concept we use is Patterns — we look for repeating results in our data.

Here is our anchoring phenomenon: A student pours orange juice into a cup and weighs it. Then she puts the cup in the freezer overnight. The next day, the juice is a solid block of ice. She weighs it again. The graph below shows what happened.

Look at the two bars in the graph. The orange bar shows the weight of the liquid juice. The blue bar shows the weight after it froze into solid ice. Both bars reach exactly 350 grams. Even though the juice changed from a liquid to a solid, its weight stayed the same. This is the pattern we are looking for!

Scientists use graphs to spot patterns quickly. Instead of just reading numbers in a table, a graph lets you see the pattern. Here is how to read a bar graph that shows weight before and after a change.

Step-by-Step: Reading a Weight Graph

• Read the title. The title tells you what the graph is about — for example, "Weight Before and After Dissolving Salt."
• Check the y-axis (up and down). This axis shows the weight, usually in grams. Each line on the axis stands for a number.
• Check the x-axis (left to right). This axis shows the conditions, like "Before" and "After."
• Compare bar heights. If both bars reach the same height, that tells you the weight is the same. This is the conservation pattern!
• State the pattern. Write or say what you notice: "The weight before and after the change is the same."

Remember, the Crosscutting Concept of Patterns helps us across all of science. Whenever you see a repeating result — like weight staying the same over and over — you have found a pattern. Patterns give us evidence to support a scientific idea.

Is the frozen juice experiment a one-time thing? Not at all! Let's look at data from three different experiments. Each one involves a physical change — a change in shape, size, or state — but not a change in the type of matter.

Notice the pattern. Even though the three experiments are very different, every pair of bars matches. The paper bars are both 15 grams. The salt-water bars are both 250 grams. The cracker bars are both 30 grams. This repeating pattern is strong evidence that weight is conserved during physical changes.

Let's walk through a full example together. Maya is making lemonade. She wants to test whether dissolving sugar in water changes the total weight.

Scientists often collect data in tables first. Then they make graphs. Both are useful, but they have different strengths. Let's compare.

So far, we have focused on physical changes like freezing, dissolving, and tearing. But what about chemical changes — changes that make a brand-new type of matter? Do those follow the same rule?

The exciting news is that conservation of matter works for all changes. In later lessons, you will test chemical changes and discover the same pattern on your graphs. As long as nothing escapes (like gas floating away), the total weight before equals the total weight after.