Energy, Machines, and Motion
Part Two: Machines
Lesson 15: The Efficiency of Machines
In Lesson 15 students calculate the efficiencies for inclined planes at different slopes and for pulleys in different arrangements.
Focus Questions: What is machine efficiency? How is machine efficiency calculated?
3. Lesson Set-up and Management
EALR 3: Application
Core content: Science, Technology, and Solving Problems
6-8 AAPA People have always used technology to solve problems. Advances in human civilization are linked to advances in technology.
6-8 AAPD The process of technological design begins by defining a problem, identifying criteria for a successful solution, followed by research to better understand the problem, and brainstorming potential solutions.
- Students learn to calculate the efficiency of inline planes and pulleys.
- Students learn that efficiency is the ratio of work output to work input for a machine.
- Students learn that machines are not perfectly (100%) efficient because of frictional forces.
3. Lesson Set-Up and Management
Materials:
- Students will not need to set up or manipulate any equipment in this lesson.
- Students will need to work with data collected in Lesson 11 and Lesson 12.
Student Management:
- Consider working through this lesson as a whole group. Students tend to not have experiences with the concept of efficiency
- Consider having group data from Lesson 11 and Lesson 12 available for students use in their calculations.
Writing Support:
- Consider pasting the chart of Efficiencies of Some Common Devices into their notebook. This will serve as a comparison for the efficiencies of the incline plane and pulley systems they will be asked to calculate. It will help them to see how the machines are much more efficient than other everyday objects students are more familiar with.
- Consider asking students- Where the energy in inefficiencies actually goes? (Answer, besides friction, there is also sound, heat, and light- depending on the system.)
Reading Support:
- An introductory reading “The Meaning of Efficiency” explains the concept of efficiency and how to calculate it.
- “Harnessing the Power of Nature” provides a historical perspective of the development of energy and power and how James Watt improved the efficiency of the steam engine.
- The third reading, “Energy Star®: A Bright Idea” discusses how to make homes and business more energy efficient.
Math Support:
- Students should find that the machines’ efficiency is less than 100%. If a student has a value over 100% discuss measurement ranges of data from the entire class. Make sure students focus on the key principle that machines are not 100% efficient because of friction.
- Simple machines that students have been studying are very efficient, motors and machines used in industry have efficiencies much lower than the simple machines students have been using.