University of Virginia
Physics Department

## Convection Currents and Density

A Physical Science Activity

### Student Activity

Materials (for each group)

• 2 ice cubes ( strongly dyed with food coloring - dark blue works well )
• fresh warm water
• tongs
• a ruler
• thermometer
• 250 ml beaker
• salt ( about 70 grams )
• stirring rod

Procedure

1. Obtain an ice cube that has been strongly dyed with food coloring.
2. Using tongs, gently place the ice cube in a beaker ¾ full of warm, fresh water. Keep the beaker and water as still as possible.
3. Observe the ice - water mixture for several minutes. Write a detailed description of your observations.
4. Measure the temperature at the surface, at the bottom of the mixture, and 3 measured levels in between. Record the temperatures in the data table.
5. Empty the beaker and fill it to the same level with warm water.
6. Add salt to the water, stirring vigorously as you pour until no more salt will dissolve.
7. Repeat steps 3 and 4 using salt water in place of fresh water.

Data Sheet

 Observations of Fresh Water: Fresh Water Salt Water Depth Temperature Depth Temperature surface surface 1/4 Down 1/4 Down 1/2 Down 1/2 Down 3/4 Down 3/4 Down Bottom Bottom Observations of Salt Water:

1. As the ice melts, what happens to the colored meltwater in the sample of fresh water?

2. In the salt water?

3. Do you observe convection currents in this activity?

4. Of the 2 liquids used, which do you think is denser?