LAB: Equilibrium and Conservation of Energy in the Global Water Cycle Name:  ______________________    Date: _____________________

Problem
A perfectly "closed" system is one in which there is no net loss with respect to a specific quantity such as mass or energy.

In this experiment you will create a mini model of the water cycle, and you will see that the water will move to different parts of the system.  You will measure the change in the temperature of the system as heat is added (from a heat lamp).  What will happen to the temperature of the system when heat energy is added for a period of time?

Your Hypothesis
Write a hypothesis about what will happen to the temperature as heat is added in the mini system for 40 minutes.
Identify the independent and dependent variables.

Materials

600 ml beaker Watch glass thermometer (deg C) 100 ml water

Heat lamp   clock   Black paper   graph paper   meter stick

Procedure
1.  Make a data table for recording temperature every 4 minutes for at least 30 minutes (or more).
2.  Place the thermometer in the beaker.  It should fit down inside the beaker.
2.  Pour 100 ml of room temperature water into the beaker and put the watch glass on top.
3.  Shine the heat lamp directly on the beaker at a distance of 20 cm from the water surface.
4.  Put the beaker on a black piece of paper.
5.  Read the thermometer every 5 minutes and continue for at least 30 minutes (more if possible).
6.  Record the time and temperature every 4 minutes.
7.  Clean up and return the equipment.
8.  Write a Lab Report.

Lab Report suggestions

Procedure
Remember to write your method in the past tense.
Include a labeled sketch of the equipment set up.

Data
Make a data table and record time and mass every 5 minutes for 45 minutes.
Make a graph of temperature vs time.

Analysis of the Results
    1.  What changes did you observe as the water was heated?
    2.  What causes these changes?
    3.  Explain the shape of your graph.
    4.  Is the mini water cycle an open or closed system with respect to energy?
    5.  Account for, and discuss, the uncertainties in your data.
 

Conclusion
    Restate your hypothesis and evaluate it.  Present the conclusions you reached about
the research question.  Make sure to explain how you arrived at these conclusions
based on your methodology and data analysis.  Show your reasoning.

Discussion
Put your conclusions in context; what do they mean?  In your discussion use the
following key vocabulary words:radiation, light energy, thermal (heat) energy, conduction, convection. thermal equilibrium, feedback loop, open system, closed system.

    1.  The heat lamp provides a constant source of energy for the system. If that is true, then how can the temperature of the water change?
    2.  Do you think there was equilibrium in the mini system?  What evidence do you have?
    3.  Was the the energy in the mini system conserved? (That means the energy was changed, but none was destroyed.)
    4.  Exactly how does the heat get from the lamp to the water?  Compare with how thermal energy gets from the Sun to the Earth.
    5.  Here is a box model of your mini water cycle showing the transfer of thermal energy.
 

This system has a feedback loop.  When one quantity changes it causes a change in another quantity, which then goes back and affects the first quantity (a loop).  Does an increase in Net energy cause the water temp to increase or decrease?  Does an increase in emitted energy cause the net energy to increase or decrease?

    6.  List the similarities and differences between the mini model and the global water cycle.  What are the limitations of this model?
     7.  Suggest a new question for further study.