Cody Svoboda

Underwater Smokestack

Scientific Concept: Density

This demonstration illustrates the concept of density. Because the hot water at the bottom of the jar is less dense that the surrounding cold water, it rises to the surface of the cold water and appears to be an underwater smokestack.

Materials:

• One liter beaker
• One small vial (about 25 mL)
• Cold water (cooled with ice and let melt)
• Colored hot water (use a dark color for best results)
• Foil
• Pencil
• Piece of string

Procedure:

Fill the liter beaker with cold water. Again use ice to make the water as cold as possible.
Fill the small vial with hot water and add food coloring to the water. Again use a dark color so it is easier for the audience to see.
When the small vial is hot put foil over the top.
With the string, tie around the top of the vial leaving enough string as a tail to be able to lower the vial into the liter beaker.
Place the vial, using the string, at the bottom of the beaker.
When the vial is sitting on the bottom, use the pencil to poke a hole in the top of the foil. Make this hole as big as the pencil so the liquid can get through.
The hot water will then rise to the surface as if it were smoke from a smokestack.

Introduction:

Have you ever gone past a huge factory and notice the billows of white smoke rise from the smokestacks? I do not have any smoke but I am going to try something using water.

*Do demo and tell them about the cold water and the vial of hot water.

Explanation:

Something with a lesser density than something else is lighter and therefore "floats" on the top of the more dense material. Because hot water is less dense than cold water, the hot water rises to the surface of the cold water. This occurrence happens just like hot and cold weather. Heat rises while cold goes down. Also with air conditioning, the higher you are in the house the hotter it feels, but on the basement floor it is completely cool. This is because cool air is the denser of the two and therefore goes to the lowest level of the house. Finally this is also how a hot air balloon is able to rise up into the sky.

Safety:

Always use beaker tongs to carry hot liquids. Carrying a stack of paper towels underneath the beaker will also make it easier to hold. Put the string on carefully so no hot liquid spills.

Waste Disposal:

Pour everything down the sink when you are done. Nothing is harmful to the sink or to the water.

Reference: Unknown