Project cost ($):
This science fair project involves a heat source and water. Care should be taken when handling these.
Convection is the phenomena characterized by the movement of molecules in gases and liquids. Heat causes molecules to be active, while cooler temperatures result in less activity. Convection can be observed in volcanoes, in the ocean, in cooking, in heating your home and even in decorative lava lamps. In this science fair project you will observe how the addition of salt to water effects convection.
Understanding how salt affects convection currents in water.
In water, convection occurs when warmer water at the bottom, rises to the surface. If the water cools near the surface it will eventually sink back again to the bottom. This rising and falling of water becomes a cycle.
Density is a measure of the amount of mass an object of a given volume, possesses. At the molecular level, water molecules are further apart from each other at warmer temperatures (as compared to lower temperatures). At warm temperatures, the water becomes less dense. At lower temperatures, water molecules are closer together, becoming denser. This is why warm water rises; it has a lower density than cooler waters.
Salinity is the amount of salt dissolved in water. Salinity affects water density. Refer to resources under the Bibliography section for more information on salinity and density.
Convection, Density, Salinity
How is density affected by salinity?
Questions & Answers
What causes liquids to rise to the surface?
As the temperature of the water increases, it becomes less dense. A lower density means the water becomes less heavy, so it moves toward the surface.
What causes liquids to sink to the bottom?
As the temperature of the water decreases, it becomes denser. A higher density means the water becomes heavier, so it sinks toward the bottom.
What determines the rate of this movement?
While temperature can affect the rate of movement, so does salinity. Ocean water has salt so it has a greater salinity than fresh water, which has little or no salt. The higher the water's salinity, the heavier is the water.
Make it Your Own
Try the science experiment with hot and cold water, instead of fresh and salt water.
? "What is Convection" at the Wise Geek website http://www.wisegeek.com/what-is-convection.htm
? "What is density?" at the Whyzz web site http://whyzz.com/what-is-density
? "What is Salinity" at the Wise Geek website http://www.wisegeek.org/what-is-salinity.htm