1. Why can't a balloon be used to travel to space? A balloon is able to rise and float on air because the helium or other gas inside the balloon is less dense than the surrounding air. As altitude increases, however, air pressure (or the weight of the air that is felt) decreases, which means the density of air is decreasing. Eventually, the density of air at high altitudes will be less than that of the air inside the balloon causing the balloon to stop rising. 2. What is thermal expansion? How does it relate to sidewalk cracks, the levees in New Orleans, and global warming? As solids heat up, the atoms move faster and therefore push nearby atoms farther and farther away. Therefore, sidewalks and levees need cracks or joints that allows the concrete material to expand at hotter temperatures. In terms of global warming, as the Earth gets hotter, the water in the oceans will also expand increasing the sea level and possibly flooding coastal areas. 3.
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