HANDS-ON ACTIVITY: POWER, WORK AND THE WATERWHEEL CONTRIBUTED BY: INTEGRATED TEACHING AND LEARNING PROGRAM AND LABORATORY, UNIVERSITY OF COLORADO AT BOULDER

KEYWORDS energy, waterwheel, work, p ower, potential energy, kinetic energy, Newtons, Joules, Wa tts energywaterwheelworkp owerpotential energykinetic energyNewtonsJoulesWa tts

LEARNING OBJECTIVES Make a connection between the concepts of power and work and engineering design Work in a design group. Explore nonlinear functions (ex. power is inversely proportional to time) Collect data to solve equations and form conclusions

MATERIALS LIST 2-liter bottle with caps ¼-inch dowel rod (must be longer than the 2-liter bottle) 15 index cards 1.2 meters of string Scissors Tape A 200 gram weight Cell phone for stop watch Electronic Scale Gallon water jug full of tap water Large orange funnel H 2 0 Solutions Worksheet, one per person

PRE-ACTIVITY ASSESSMENT Brainstorming: Write down all the groups' ideas to share with the class. "What features make a good waterwheel?"

INTRODUCTION Power and work are important concepts that impact the engineering design of items ranging from racecar engines to elevators to power plants. High-power cars (high- horsepower) are able to accelerate very quickly and go very fast.

Elevators in skyscrapers require enough power to lift many people quickly, to avoid long elevator waiting lines. As we'll see, power plays an integral role in the production of hydroelectricity. Work is measured in Joules (J) and is defined as a force acting over a distance or: Work = force x distance

In our activity today, work will be done lifting a weight. The force term equals the weight and the distance term equals the height lifted. Power is measured in Watts (W) and is defined by how fast work is done or: Power = Work ÷ time

In this activity, you are working for H 2 O Solutions, an engineering design firm that works mostly with waterwheels and water energy! Your city wants to use hydropower instead of coal to make energy because they are worried about air pollution. The city has hired you to design an efficient watermill.

The firm (our class) has been split into several engineering teams (student groups). Each engineering team will design and test a slightly different design so that the firm can present the most efficient design to the city. You will calculate power and work by measuring force, distance and time for your team-built waterwheel.

PROCEDURE Pass out worksheet Drill 3/8-inch holes into the end of the two-liter bottle and the cap. This allows the bottles to spin symmetrically and freely about the dowel rod. (If you don’t have the hole in the cap, the dowel rod will not spin symmetrically.)

1.Get into groups. 2.You are all engineers designing a water wheel. You must keep all data on the design sheet. 3.Use the index cards and the plastic bottle to make a water wheel. Come up with multiple ideas and discuss how to attach them. The water will be supplied from a pitcher through a funnel and the bottle will spin on the dowel rod.

4.Tie the string to the cap end of the bottle so that when the bottle rotates, the string wraps around the bottle neck, pulling up the string. 5.Measure and tie a 200 gram weight to the other end of the string. Multiply the mass by gravity (9.8) to calculate your force.

6. Test the waterwheels by pouring water through a funnel to achieve an even flow, and timing how long it takes to lift the weight 1 meter (This is your distance). Perform this test outside. Two students hold the ends of the dowel rod, one student pour the water and one student time how long it takes and write it down.

7. Have the students calculate the work and power of their waterwheel. Work = force x distance Power = Work ÷ time 8. Which team had the most power?

Safety Issues Make sure the students do not use the dowel rods inappropriately. If testing inside and on tile, the floor may be slippery when wet.

POST-ACTIVITY ASSESSMENT Explain the difference between work and power in your own words.

EXAMPLE POWER PROBLEM Mr. Muscles loads up a bar with 910 Newtons (≈205 lbs) of weight and pushes the bar up over his head 8 times. Each time he lifts the weight.5 meters. How much work did he do? If he does the whole thing in 15 seconds, how much power did it take?