What is Power?

6 teachers like this lesson
Print Lesson


Students will be able to describe the relationships between power, work and time and solve problems for each of quantity.

Big Idea

Students use work to help them solve for power.

Review Power Notes

10 minutes

The goal of this lesson is for students to be able to recognize the relationships between power, work and time and to calculate power. Students have learned about work in the previous lesson so they can use that knowledge to help them complete some types of problems. This lesson focuses on students' ability to use computational thinking (SP5) as well as communicating information to other students (SP8). Learning about work in the pervious lesson and power in this lesson will lead to energy and energy conservation as in HS-PS3-1.

To start out class, I review the notes that they took for homework by asking them questions about what they learned. I start out by asking what they learned about power and record the answers on the board. As I go through their responses, I am looking for them to discuss the relationships between work, time and power, the units of each quantity, the equation and definitions. To finish out the review of the notes, I have them complete a problem that I show on the board. I go over by allowing students to volunteer to tell me how to complete each step. The problem is shown below:

During the Powerhouse lab, Jerome runs up the stairs, elevating his 102 kg body a vertical distance of 2.29 meters in a time of 1.32 seconds at a constant speed. 


Power Problem Set

20 minutes

After we have reviewed the notes and have done another practice problem, I have students complete the Power Problem WS. They work in their table groups to complete these problems. I give them time in class for this instead of focusing on the notes in class because I want to be able to walk around and catch any major mistakes that students make as they are doing the problems to prevent any misconceptions. As students are working I walk around to help students that I targeted as needing more help from the work checkpoint in the previous lesson. Since students are working with their table groups, I see that students are moving quickly through the problems and if they get stuck they ask members of their group.

Whiteboard Carousel

15 minutes

After students have completed the power problem set, I ask them to whiteboard their answers. Since there are 10 problems I ask three groups to volunteer to complete two whiteboards. I put a table up on the board so that students can sign up for the problems that they would like to complete. Once they have signed up for their problem they may begin working on their whiteboard.

Because there are so many problems, I do not have the students participate in a traditional whiteboard session where they present to the class. Instead I have them set their problems up around the room and give them 45 seconds to look at each board to see if they did the problem correctly. As you can see below, it can get a bit chaotic but it is the best way to get through the answers in a short time.

Shown below are a few of my students' whiteboards. You can see that they include their equation in symbols, show their work and their numerical answer with units. Since these problems are not too complex, this type of whiteboard session allows students to see all of the work but check their answers quickly. At the end of this session I have them give me a thumbs up if they got most to all of the problems correct, thumbs sideways if they got about half correct, and thumbs down if they got most of them wrong. Overall I see that most students were successful in this work sheet and feel fairly confident about work and power.

Work and Power Rally Coach Activity

20 minutes

After students finish checking their answers with the carousel, students get their speed dial cell phones from the class distributor. I select a speed dial number and ask them to make eye contact with their partner. I make sure everyone has a partner (especially if there are students that are absent) and when all students know who their partner is, I have them move to sit next to their partners so there is only one pair at a table. 

We have done Rally Coach activities before so first, I pass out the Rally Coach Work and Power worksheet and have students put a partner's name in each name box at the top of the page. Then I ask students to explain how this activity works to remind anyone who does not remember. In this activity students are in charge of writing the answers for each problem in their column. So there is no confusion, I ask the students to raise their hand if their name is on the left side of the page and tell them that they are in charge of the left two problems and then the same for the right side. Both partners will be getting the same grade so to ensure that they agree with what their partner wrote, they must check their work and come to a consensus before they hand it in.

After I give instructions, students have 20 minutes to complete this activity. As they are working, I remind them that they should be asking their partner for help first and if both of them do not know and they have consulted their notes, they can raise their hand and I will come over to help them. I collect the worksheet when they are done and grade it to give back to them the next day.

Power Checkpoint

5 minutes

To end class, I want to see what students can do on their own with work and power so I give them this Power Checkpoint about Atlas and Hercules. I find that I can see who has a misconception that if someone does more work, he automatically has more power. If students can use the equations correctly, this checkpoint is pretty easy. I find that this is also a place where I can see if students remember that mass is not the same as force. You can see in the Power Checkpoint Student Work that both of the misconceptions are shown. I had many students forget that mass is not force but fewer students jump to conclusions straight from work to power.