Fill an empty plastic bottle with one cup water and one cup rubbing alcohol. Add food coloring so the liquid will be easier to observe. Place a clear drinking straw into the bottle but do not let it touch the bottom. Use modeling clay to cover the top of the bottle and keep the straw from moving. Set up the thermometer in a warm place such as a window and observe what happens to the liquid. When the liquid is heated it will expand causing it to rise in the straw. If the air temperature is cold, the liquid will contract resulting in lower levels of liquid in the straw.
Cut off the bottom of a balloon and stretch the remaining top over the mouth of an empty jar. Tape a drinking straw to the middle of the stretched balloon. Secure a piece of paper to a wall with tape and place the jar in front of the paper. The straw should be straight and parallel to the ground. Make a mark on the paper indicating the position of the level straw and label the line as sea-level pressure. Label the area above the line as high pressure and the area below the line as low pressure. Changes in pressure will force the air in the jar up or down depending on the pressure change therefore moving the straw. High pressure will push down on the balloon causing the straw to move up while low pressure will cause the balloon to expand outward pushing the straw downward.
Prepare a tray of ice cubes adding one drop of blue food coloring to each cube and freeze overnight. Fill a clear plastic tub three-fourths full with room temperature water. Prepare two cups of warm water and add red food coloring. Place one blue ice cube at one end of the tank and pour half of warm red water at the other end. As the blue cube melts, it should sink to the bottom while the red water should rise to the top. Cold water is more dense than warm water so it will sink to the bottom. The same process can be observed in the Earth's atmosphere. Warm air, which is the main ingredient to the formation of thunderstorms, rises leaving the cold air at the surface.
Fog is essentially a cloud on the ground. The air temperature and dew point, or temperature at which dew forms on the ground, are the same causing condensation to occur. Fill a cup three-fourths of the way with warm water. Allow the cup of warm water to stand for one minute. Pour out most of the hot water leaving a few inches at the bottom. Place a strainer over the top of the cup and place two ice cubes into the strainer. Fog should begin to form due to the warm and cold air meeting and condensing.