Power Run

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Students apply the concepts of work and power as they race up several flights of stairs.

Big Idea

Power, measured with the SI Unit of watts, is the rate at which energy is transferred into or out of an object or system and is measured using the formula P=W/t.

Context and Supplies

In the previous lesson, Work, Power and You, students applied the the physics concepts of work and power to the motor that lifts a roller coaster to the top of its first hill.  Students apply the concept of work and power to themselves and their peers as they race up the stairs. By racing up two flights of stairs, students store potential energy into their bodies. They can calculate the total power required to lift their bodies to the top floor by dividing the change in potential energy by the time it take to make the trip. Stop watches and a ruler or meter stick are needed. Also several able bodied students who want to show off their athletic prowess.  

To complete this activity, students apply Science Practice 4, analyzing and interpreting data, Science Practice 2: Developing and using models and Science Practice 5: Using mathematics and computational thinking. NGSS HS-PS3-1, the performance standard for Energy, relates to this activity. Students create a computational model to calculate the change in the energy of one component, identify the reference level for potential energy = 0 and map the energy flow in the system, all expressed in joules and watts.

Do Now: Power Calculation

5 minutes

I open the class with a brief review of the work and power formulas that is in the Sample Power Problem power point. Then we work through a sample calculation of the power requirement to lift a Quarter Pounder from the table to your mouth. Students are expected to write this example in their notebooks as I call on students to supply variable values required to lift a hamburger. This sets the stage for the coming activity, where students apply the same calculations to determine the power required to lift their own bodies up the stairs.

Grouping Students for Power Run

5 minutes

This section starts with the Power Run power point on the first slide which has a visual of the activity and the roles. The goal of this activity is to determine who in this class has the greatest power production. All students have a job to do. The roles are: runner, timer, recorder and diagram maker. The runner is the student whose power production is calculated. They start on the bottom floor and run up two floors as fast as they can. The timers are at the top floor and they measure the time it takes the runner to get to the top. The recorders are on the middle floor and they write down the important data. The diagram maker makes the diagram of the power run on the final report.

I choose one student from the class to be the ring leader, the one who runs the activity. I pick someone who is bold and loud and does not have a problem clearly communicating with others. This person will check to see that the runner is ready and that the timers are ready. Then they will count down "3-2-1-go" to start the timing. This is a necessary role as the runners are two flights below the timers who are at the top.

Form Student Groups

Students are to be in groups of 3: recorders, diagram makers and runner or timer. I ask who in the class would like to show off their athletic talents by doing the power run (it has never been a challenging finding runner volunteers). I have the volunteer runners stand-up. I then ask for timer volunteers and have them stand up. Each person standing is the nucleus of a group. The rest of the students join one of the students who are standing to form groups of three. Each group determine who is the recorder and the diagram maker. 

My class has 28 students. One is the ring leader so that leaves 27. In order to have three students per group, I need 9 groups. So I ask for 5 runners and 4 timers to stand and the remaining students join one of the standing volunteers.

Cooperative learning is used for the power run activity. This works out well as different students have different roles (runner, timer, data recorder) in order to collect the data.  It also ensures that all students engage in the activity as they have a specific job to do. Students have to work together to analyze the data and create a coherent report. I separate the students into groups of 3 (method detailed below) where each group is responsible for passing in a one page report on their power calculations and analysis. After the data is recorded, the timer or runner is responsible for doing the calculations. This prevents these students from remaining inactive while the group completes the report.

Power Run Activity

40 minutes

Once the groups are in place, I display the rubric for the report which is the second slide of the Power Run power point. It is important to make the learning goals clear and to give students clear expectations of what I want to see for the report. With clear expectations detailed on the rubric, students know what they need to do and why.

I give the students 5 minutes to determine their various roles and how they will perform the activity. Also, the runners need to measure their mass. I have a kilogram scale at the front of the room. I mention to the class as a whole that they will need a ruler or meter stick for this challenge and I put the measuring devices (stop watches and rulers) in a place for the groups to collect them. Most groups realize that they will have to measure the change in height of the runner. I use this time to prep the ring master so that they know how to run the activity efficiently and quickly.

The activity is done in the stairwell. For safety, the stairs must be empty of people while a student does the power run. I inform students at the bottom and at the top to communicate to the ring master that they are not ready if anyone is using the stairs. We wait until the stairs are clear before beginning. Depending on class size, the activity takes 10-15 minutes to conduct. While it is happening, I get to be an observer. With the roles given to the students, they conduct the activity from beginning to end. When the activity is over, the students have about 15 minutes left to complete their reports.