Hands-On Activity Instructions

Question

In the last lesson, we investigated the appearance of a substance when it changes phase. Today, we will complete an activity that will allow us to observe one or more phase changes. Read the instructions below. Then, complete this activity.

Photo of a plastic cup placed upside down on top of a foam cup.
Setup Instructions

Make sure the foam cup is filled with hot water. It should be one-quarter full.
Take the plastic cup and turn it upside down. Place it on top of the foam cup.
Observe any phase changes that occur, using the provided magnifying glasses as needed.
Answer the questions below.
What did you observe happening in the cups?

Answer 1

In the described setup, we can expect to observe several interesting phenomena related to phase changes as a result of the interaction between the hot water and the upside-down plastic cup.

Observations

1. Condensation: As the hot water in the foam cup heats the air inside the plastic cup, the surface of the plastic cup may become cooler than the warm, moist air inside the cup. This can lead to water vapor in the air condensing into liquid water droplets on the inside surface of the plastic cup. You might notice these droplets forming and accumulating, eventually dripping back down into the foam cup.

2. Temperature Change: If you use a thermometer, you might notice a decrease in the temperature of the air inside the plastic cup as it loses heat to the surrounding environment and the foam cup. Conversely, the water in the foam cup will remain hot for some time, providing a continuous source of heat.

3. Phase Changes: This activity can illustrate both condensation (gas to liquid) and potentially evaporation (liquid to gas) if the water in the foam cup is hot enough. The hotter the water, the more likely it is that some of it will evaporate into the air, leading to steam or vapor that may also condense on the cooler surface of the plastic cup.

Conclusion

Overall, the primary observation is the formation of water droplets on the inside of the plastic cup due to condensation, demonstrating the transition from water vapor (gas) to liquid water. The interaction between the hot water and the ambient conditions illustrates key concepts of thermodynamics and phase changes in a hands-on way.