2003 Virginia SOLs
Motivation for Learning
Show the students a balloon that is filled with helium. Have a string tied to it and note that it floats in air. Ask students, "What type gas is in this balloon? Why does it float in the air?" Students should know that the balloon is filled with helium. Ask them what other gas might it be filled with? (hydrogen). Ask students to predict what will happen when you gently warm balloon containing air with a hair dryer.
Density is the amount of matter per volume of D = M/V. Another way this can be explained is density is the amount of matter per space or how much stuff is in one area. Matter is constantly moving. Even molecules in the solid phase vibrate a little bit. Matter, or molecules, in a gas moves much faster and are further apart. There are fewer molecules per space in the gas phase than for liquids and solids. When heat is applied to any matter, the molecules speed up, start bouncing off each other, and tend to spread apart. Consider a balloon filled with air that we heat with a hair dryer. The balloon will expand, occupying more space. The number of air molecules is the same, but the volume has increased, causing the density to decrease. The balloon's volume is less dense than the space around it. Same amount of matter, different amount of space. As the balloon cools, the molecules will slow down, move closer together, and the balloon will sink to the floor.
Students with Special Needs
All students should be able to participate in this activity.
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