Cool & Hot together!


  1. Two transparent plastic bottles
  2. Water
  3. Blue food coloring or blue ink
  4. Red food coloring or red ink
  5. A saucepan
  6. A thick piece of sheet such as an index card


  1. At first fill one plastic bottle with water.
  2. Then add some blue food coloring or blue ink in it.
  3. Now place the bottle inside the refrigerator for about one hour.
  4. Before getting the bottle out of the refrigerator, use the sauce pan and the oven/stove to heat enough water to fill the other plastic bottle bottle. Be careful not to boil the water. Otherwise some of the water will be vaporized. But heat the water pretty well.
  5. After heating the water fill it in the other plastic bottle.
  6. Then add some red food coloring or red ink.
  7. Now take the blue water bottle out of the fridge and place it on a flat surface.
  8. Hold the thick piece of paper (Such as an index card) on the top of the opening of the red water bottle.
  9. Then quickly invert the red water bottle over the blue water bottle and line up the bottle openings.
  10. When the plastic bottle openings are perfectly aligned, carefully slide the thick paper out from between the bottles.
  11. Now create a chart just like the one shown below and record what happens.

Red Bottle

Blue Bottle


The cold blue water stays on the bottom and the red hot water stays on the top.


This experiment/project shows the advantage of the effect of temperature on density. A cooler liquid is much more dense than a warmer liquid. The molecules in cool water move around lesser than molecules in hot water. They have less energy to spare for motion because the temperature is lower. It’s because the cold water molecules move less, more molecules may be packed into the same total volume than in the case of hot water. This makes cold water much more dense than hot water.
On the other hand, because of the difference in density, the hot water tends to float on top of the cold water rather than mix with it. This is why the colors stay separate. The longer the hot and cold water are left within contact, the closer their temperature will become. Eventually the blue and red water will begin to mix with one another.

  1. Try the same experiment again. Only this time place the cold water bottle over the hot water bottle.
  2. Observe the difference between the amount of motion in the molecules of hot water against the motion of molecules of cold water by adding three drops of food coloring or ink to a cup of refrigerated water. Also add three drops of food coloring or ink to a cup of heated water. See in which cup does the color blend first?


You May Also Like...

Popular Posts