ACES Activity of the Week: Water Density Experiment


Participants: 5 adults (parents) and 3 kids. Yes, we had more participation from parents this week.

"Has anyone gone swimming in a lake or unheated pool?" "If yes, what did you notice about the temperature of the water at the surface and temperature of the water at the bottom?"

These questions led the way to excited discussion among the participants and it didn't take long for the group to gain consensus on the answer - "Temperature on the surface is warmer than the temperature at the bottom".

Armed with this knowledge without further ado we launched our experiment. Each participant was handed four empty plastic water bottles, two food colors (red and green) and an index card. Participants were asked to fill two bottles with warm water and the other two with cold water. Red food color was added to warm water bottles and green to cold water bottles.

Take one set of warm and cold water bottles. Place the index card on the warm water bottle and flip it and place it on top of the cold water bottle (warm water on top and warm water on bottom). Now take the 2nd set and place the index card on cold water bottle and flip it and place it on warm water bottle (cold water on top and warm water on bottom). Observe what happens for next 15 mins.

After 1 min After 5 mins

After 10 mins After 15 mins

Observations:

Even after 15 mins, the colors in the setup with warm water on top and cold on bottom did not mix, whereas the colors in the setup with warm water on the bottom and cold on the top, mixed almost immediately resulting in murky brown/grey color.

Discussion about science behind the experiment:

Different temperature water has different density. Colder water is more dense and will weight more for each cubic foot of space. In the setup with warm water on the top, warm water is less dense than colder water and hence stays (or floats) on the top. The hot water stays elevated above the colder (blue) water. In the setup with warm water on the bottom, the warm water will rise, but in the process the red coloring will mix with the green food coloring in the cold water and result in brown/grey water.