Students drop water from different heights to demonstrate the conversion of water's potential energy to kinetic energy. They see how varying the height from which water is dropped affects the splash size. They follow good experiment protocol, take measurements, calculate averages and graph results. In seeing how falling water can be used to do work, they also learn how this energy transformation figures into the engineering design and construction of hydroelectric power plants, dams and reservoirs.
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- Colorado: Math
- Colorado: Science
- a. Identify and describe the variety of energy sources (Grade 4)  ...show
- Common Core State Standards for Mathematics: Math
- 3. Draw a scaled picture graph and a scaled bar graph to represent a data set with several categories. Solve one- and two-step "how many more" and "how many less" problems using information presented in scaled bar graphs. For example, draw a bar graph in which each square in the bar graph might represent 5 pets. (Grade 3)  ...show
- 6. Find whole-number quotients of whole numbers with up to four-digit dividends and two-digit divisors, using strategies based on place value, the properties of operations, and/or the relationship between multiplication and division. Illustrate and explain the calculation by using equations, rectangular arrays, and/or area models. (Grade 5)  ...show
- 7. Add, subtract, multiply, and divide decimals to hundredths, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used. (Grade 5)  ...show
- International Technology and Engineering Educators Association: Technology
- C. Energy comes in different forms. (Grades 3 - 5)  ...show
- Next Generation Science Standards: Science
- Use evidence to construct an explanation relating the speed of an object to the energy of that object. (Grade 4)  ...show
- Develop a model to describe that when the arrangement of objects interacting at a distance changes, different amounts of potential energy are stored in the system. (Grades 6 - 8)  ...show
- Describe an object's varying potential energy as being dependant on its height above the Earth's surface.
- Explain the path of potential energy converted into kinetic energy as objects fall.
- List ways that the energy of falling water is used to do work.
- Describe how engineers use the potential and kinetic energy measurements of water to design reservoirs and hydroelectric power plants.
- Plastic straw (clear is best)
- Cup or glass (to hold colored water for dipping the straw)
- Meter stick
- Pencil or pen
- Marking pens
- Newsprint, newspaper or blank paper (minimum of 12-16 sheets per team)
- 1 or 2 plastic, gallon-size (3.78 liter-size) milk containers to distribute water
- Water, preferably colored with food coloring
- Falling Water Worksheet, one per team
|The straight-line distance across a circular area, through its center point.|
|The ability to do work.|
|A power plant that uses water turbines to generate electricity.|
|Electricity produced by the energy of running water.|
|The energy of motion. For example, a spinning top, a falling object and a rolling ball all have kinetic energy. The motion, if resisted by a force, does work. Wind and water both have kinetic energy.|
|Energy that can be used to do work. It is the sum of an object's kinetic and potential energy.|
|Potential energy is the energy stored by an object as a result of its position. For example, a roller coaster at the top of a hill, or water being held behind a dam.|
|Energy that is made from sources that can be regenerated. Sources include solar, wind, geothermal, biomass, ocean and hydro (water).|
|A machine in which the kinetic energy of a moving fluid is converted into mechanical energy by causing a series of buckets, paddles, or blades on a rotor to rotate.|
Before the Activity
- Gather materials and make copies of the Falling Water Worksheet.
- Fill the containers with water. Color the water with several drops of food coloring.
With the Students
- Divide the class into teams of three or four students each.
- Show the students how to use a straw like a water dropper (see Figure 1). Stick the straw in a glass of water. Place a finger on the top of the straw. Pull the straw out of the glass, while still holding your finger over the top. Hold the straw over a piece of paper and remove your finger.
- Ask the students how they can all be sure to use the same amount of water for each trial. (Answer: By marking a line on the straw and always refilling it to that point.)
- Discuss with students methods for measuring the diameter of a splash. Have the students agree on a standard class method for determining the diameter of a splash. Have students use a pencil or pen to outline the splash, and label it with their name, the drop height, and the splash diameter.
- Have student teams describe on the worksheet what they predict will happen to the splash as it is dropped from increasing heights. Do they expect the size of the splash to increase or decrease with higher drop heights?
- Have the class agree on four heights from which to drop the water, such as 30 cm, 60 cm, 90 cm and 1 m (note this on the worksheet). Teams measure the diameter of the water splash for all four heights. Each team member drops the water once from each height. Thus, teams with three members have 12 data points and teams with four members have 16 data points.
- Students take turns doing each part of the activity. One student holds the meter stick. One student drops the water using the straw. A third student measures the splash diameter.
- Hold the bottom of the straw at the height by first placing it next to the correct height on the meter stick and then moving it several centimeters away, being careful to keep the straw at the same height. On the paper, write the height, diameter and team member name, and record the data on the worksheet.
- After one person drops the water, the team members switch places and repeat the process. The student measuring the diameter of the splash moves the paper so the water falls on a dry piece.
- After teams have finished their drops, have them complete the worksheet by calculating averages and creating a graph of their average data.
- Conclude with a class-wide comparison of each team's results (table data and graphs) and a concluding discussion, as described in the Assessment section.
- Remind students that wet floors can be slippery and to be careful in areas in which water is being used.
- True or False: An object's potential energy depends on its height above the Earth's surface. (Answer: True)
- True or False: Kinetic energy is the energy of something staying very still. (Answer: False. Kinetic energy is the energy of an object in motion.)
- True or False: An object's kinetic energy increases as its speed increases. (Answer: True)
- What makes a good experiment? Only one variable can be changed at a time in a good experiment. Why?
Activity Embedded Assessment
- Amount of water being dropped
- Measurement of the splash diameter
- Height from which to drop water
- What patterns do we see in the results? How might we have altered the experiment or our methods to make a better experiment? What conclusions can we draw?
- What happens when we increase the height from which the water is dropped? What if a light bulb is dropped from 1 cm off the floor? From 2 meters off the floor? How does the potential energy and the resulting force (kinetic energy) change in these two cases? What if you dropped a glass into the sink? Does the height at which it is dropped make a difference in whether it breaks or not? How is a short waterfall different from a very high waterfall?
- How would engineers use this understanding to design hydroelectric power plants? How would engineers use this understanding to design roller coasters? How is the force you feel on a roller coaster different if you are coming down a steep section compared to a level section?
- Draw the transformations of energy that occur when an object is dropped. (Answer: Potential energy due to the object's height above the Earth is converted to kinetic energy as it falls. Note: Point out to students that when the object strikes the Earth, the kinetic energy is converted into other forms of mechanical and potential energy, such as sound or heat energy. It may be appropriate to explain that energy may change its form, but there is no net change to the amount of energy. This is called conservation of energy.)
- Draw the transformations of water energy as it goes from a reservoir through a hydroelectric plant.
- Use your understanding of kinetic energy to explain why engineers place some hydro generators in fast-moving waters. (Answer: Fast moving waters have more kinetic energy to transfer to the blades of a turbine, making them spin faster than they would in slow moving waters.)
- Use your understanding of potential and kinetic energy to explain why engineers build large dams for hydroelectric power plants. (Answer: The dams hold back large amounts of water. The water is higher than the turbines so it has potential energy. As the water moves downward to the turbines, its potential energy is transformed to kinetic energy, turning the blades of the turbine.)
- A 2-ml drop of water dropped from 2 meters, or a 2-ml drop of water dropped from 1 meter? (Answer: The 2 ml drop of water dropped from 2 meters.)
- A 4-ml drop of water dropped from 3 meters, or a 2-ml drop of water dropped from 3 meters? (Answer: The 4-ml drop of water dropped from 3 meters.)
- A 1-liter bottle of water dropped from 2 meters, or a 1-liter bottle of water dropped from 6 meters? (Answer: The 1-liter bottle of water dropped from 6 meters.)
- For upper grades: Using their graph results on the worksheet, have students make and test predictions for what would happen at intermediate heights and heights greater than 1 meter. Are their predictions correct?
The Artist with a Camera. Tennessee Valley Authority. Accessed October 31, 2005. (Story of TVA photographer Charles Krutch) http://www.tva.gov/heritage/camera/
The Nature of Water Power, Curriculum Units. Foundation for Water and Energy Education. Accessed October 27, 2005. (Activity adapted from this source.) http://www.fwee.org/TG/curriculum.html
Verdant Power, LLC. Accessed October 27, 2005. (Engineers who design underwater turbine power generating systems) http://www.verdantpower.com
Xochitl Zamora-Thompson, Sabre Duren, Natalie Mach, Malinda Schaefer Zarske, Denise Carlson
© 2005 by Regents of the University of Colorado.
Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder
Last modified: November 26, 2015