Mr. Sohmer showed another QuickTime video, with the red Air Puppies moving much faster than the blue Air Puppies.

“This is a nifty picture definition of what heat is. The red Air Puppies are pounding on everything much more than the blue Air Puppies are—so we could say they are hot, and the blue puppies are cold. But as long as the blue puppies are moving at all—and they always will be—they will have heat energy. Even ice has heat!”

Mr. Sohmer added another variation to the story. “How about if we had our regular situation, with 100 puppies on one side and 100 puppies on the other, the same amount of excitement activity on both sides, but we make the room on the right bigger. What would happen to the wall then?”

“The wall’s going to move to the right,” Pedro said.

“Why do you think that?” asked Mr. Sohmer. “What’s making the wall move? Is it getting sucked over?”

“No, it’s getting pushed. There’s more space on the right, so the puppies bop around the same, but they don’t hit the wall as often.”

Mr. Sohmer then added another aspect to the problem by asking students to imagine what would happen when each room had an equal number of Air Puppies, but the room on the right had an open door (see Figure 4-9). The students reasoned that as Air Puppies escaped from the open door on the right, the wall would move to the right, resulting in the room on the right getting smaller and the room on the left getting bigger.

“What if you close the door after a lot of Air Puppies have already escaped from the right side?” Gina asked. “There’s going to be lots of space, and lots of puppies, on the left side, and then the wall between them, and then only a little teeny space over on the right side with hardly any puppies. But can the wall just destroy the puppies on the right?”

“No, they won’t be destroyed,” Mr. Sohmer said. “They’ll still be there, still be bumbling and bouncing around.”

“Then it seems like at some point, after a long time, the wall is going to come to some kind of balance point. It’s going to be somewhere way over on the right side, but it’s gonna eventually stop.”

“If the wall stops moving, does that mean there’s no more pressure, no more puppy hits per area?” asked Mr. Sohmer.

“No,” Gina said. “I think I get it. If the wall’s not moving, it just means that there’s the same number of hits on both sides, or equal pushes, or equal forces. Like when you had two guys pushing you the same on both sides and you didn’t move. So I guess you were like the wall!”

FIGURE 4-9 As Air Puppies in the right room bumble randomly out the open door, there are fewer and fewer Air Puppy impacts on the wall from the right. Increasingly unopposed Air Puppy impacts from the left push the wall to the right.

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