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had the biggest lung capacity in the class, proving that air was present.

Marisa agreed. She’d been able to see her breath push the water out of the upside-down jar. “Air is something. You could see the air bubbles coming from my lungs.”

“And you can see air in the winter when you go outside and blow.” Jenna said. She blew hard on her hand. “It’s like wind. You can’t see it, but you can feel it.”

To investigate the properties of air, Mr. Figueroa had brought in two volleyballs and a bicycle pump.8 While his students were at gym, he put the volleyballs on the Harvard pan balance and adjusted the scale so they balanced perfectly, then he took them off. When the kids returned from gym, Mr. Figueroa called them over to the rug for “Circle Time.”

“Look at these two balls. They’re both volleyballs, and they’re both the same size, but one is dark and one is light colored. When I put them on our pan balance, one on each side, what do you think will happen?”

“They’ll balance,” called out Jocelyn. Others chimed in: “Balance.” Someone else said, “They’ll be the same.”

“Why do you think that?” asked Mr. Figueroa. Gemma waved her hand. “Because they’re the same everything. Same size, same, um, leather covering, just like when we weighed and graphed our density blocks. If it was the same size and same material, they weighed the same.”

Everyone seemed to agree, so Mr. Figueroa put the two volleyballs on the pan balance (Figure 4-3). The balance arm wobbled a bit for a moment and then came to rest in a balanced position.

“They balance. I was right,” said Gemma.

“Okay,” said Mr. Figueroa, “but here’s the investigation for today. I brought a bicycle pump from home that lets me pump air into things. I’m going to pump air into the light-colored volleyball—15

FIGURE 4-3 Light- and dark-colored volleyballs on balance.

pumps.” He inserted the needle of the bicycle pump into the volleyball. He pumped 15 times while the kids counted, “One, two, three, … thirteen, fourteen, fifteen.” (See Figure 4-4.)

“Okay, so now our light-colored volleyball has 15 pumps more air in it. So did that make it heavier? Lighter? Or still the same weight? When we put this volleyball back on the pan balance, is it going to go down?” He tipped his body to the left. “Is it going to go up?” He tipped his body to the right. “Or is it going to stay balanced?”