Ask students to volunteer to be the edge of the solid. Line up the volunteers to make the edge of the solid then place students inside the boundary. Place students next to each other so that they do not have room to move around. They should be standing shoulder to shoulder. Once the students are in place, ask them if they can move about freely. The answer, of course, is no. Explain to them that molecules in a solid cannot move about freely because they are so close together. Ask them if they can think of a way for the molecules to move. Then, explain to them that the molecules in a solid move by vibrating.
Now have students become the molecules in a liquid. Have students volunteer to be the boundary for the liquid and place students inside the boundary. This time place students a little further apart where they have some room to move. Ask students if they have room to move now, which they do. Ask them if they have a lot of room to move, which they do not. Have students move around slowly flowing by each other. Then, explain that molecules in a liquid move that way.
Now have students become the molecules in a gas. Again, have students form a boundary for the gas and place students inside. This time you will need to have a bigger boundary and place students farther apart. Ask students if they have room to move around. They will have lots of room to move around. Have them move around and explain to them that molecules in a gas are very far apart and move around rapidly.
Go back to your classroom and debrief. Talk about what you did. Have students write in their science journals or on notebook paper in their own words how molecules move in a solid, liquid, and a gas. Then, read about the three states of matter in your science textbook or from information that you will provide.