Try It on Cold
Once you see the thermometer go up, it’s time to see it go down. You can make this happen by exposing it to cooler temperatures. We took ours outside where the temperature was in the 30s, so the solution in our straw shot down fast below the surface.
The solution will contract and move down the straw when cooled, because the molecules in the solution are moving slower and drawing them closer to each other.
If you live in a state that’s always warm, you can try this out in your refrigerator or freezer. Matter of fact, take the thermometer around to different spots in the house, warm it up with your hands, cool it down by rubbing ice around it. See how quickly you can get it to go up and down.