Hot Water/Cold Water

Author: Caryn Asherson and Alex Nighbert
Discrepant Event - Teacher's Guide
SED 695B
Detailed Explanation of Discrepant Event

Principles ilustrated

  • Density
  • Convection Currents
  • Differential Heating

1. Fill one of the jars with hot water and add a drop of red food coloring.

2. Fill the other jar with cold water and add a drop of blue food coloring.

3. Place an index card over the jar of cold water. With one hand, press lightly on the index card; with the other hand, pick up the jar and turn it upside down.

4. Place the inverted jar of cold water on top of the jar of hot water. Be sure that the mouth of the top jar is exactly over the mouth of the bottom jar. Carefully slide the index card from between the two jars.

5. Repeat the above procedures, only this time, place the hot water on top and the cold water on the bottom.


  • Students know heat from Earth's interior reaches the surface primarily through convection.
  • Students know convection currents distribute heat in the atmosphere and oceans.
  • Heat moves in a predictable flow from warmer objects to cooler objects until all the objects are at the same temperature.

Questioning Script

Prior knowledge & experience:

Have you ever noticed that the Italian dressing inside your refrigerator is divided into two layers if it has been sitting still for a while?

Why do you think that happens?

Do you think that a change in temperature can change the density of a fluid?

Let's say you walk into the kitchen in the middle of the night for a midnight snack. You are barefoot and you open the fridge. Which part of your body is more likely to feel the cold, your feet or your nose?

Have you ever noticed that the water on the bottom of the swimming pool is colder than near the surface?

Have you observed what happens when cold milk is poured into a cup of hot coffee?

Have you noticed that hot air balloons rise when heat is fired into the balloon?

Root question:

Does temperature of a fluid affect its density?

Target response:

What happened when the index card was removed from between the two jars?

[The water in the two containers mixed when the hot water was at the bottom.]

Which jar contained hot water and which contained cold water thirty seconds after the completion of procedure 4?

[As the hot and cold water mixed after the card was removed, the temperature of the water in both glasses was approximately the same.]

What happened when the hot water was on top?

[When the hot water was placed on top and the card was removed, the water did not mix.]

What does this activity show?

[This activity demonstrates that hot water is less dense than cold water and that hot water and cold water will mix (form a current) until the temperature equalizes.]

Common Misconceptions:

Color has something to do with the reason the water mixes or doesn't.


References & Links: