Energy, Machines, and Motion
Part Two: Machines
Lesson 14: The Mechanical Advantage of Machines
Students develop an understanding of the work done by machines and the relationship between forces and the distances through which they act by calculating both the ideal and actual mechanical advantage of the inline plane and pulley.
Focus Questions: What is the difference between ideal and actual mechanical advantage? How are ideal and actual mechanical advantage 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 will learn that ideal mechanical advantage is the ratio of effort distance to load distance when a machine does work.
- Students will learn that actual mechanical advantage is the ratio of the load force to effort force needed to lift a load.
- Actual mechanical advantage is less that ideal mechanical advantage because of friction.
3. Lesson Set-Up and Management
Materials:
- Students do not need to set up or manipulate any equipment in this lesson.
- Students 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 much outside experience with the concept of Mechanical Advantage.
- Consider having group data from Lesson 11 and Lesson 12 available for students use in their calculations. Students can easily confuse distance and force when transferring data from previous data sheets.
- The Teacher’s Edition states that students will probably need guidance for calculating ideal and actual mechanical advantage.
Writing Support:
- Students are asked to describe the difference between ideal and actual mechanical advantage. Consider having students draw and label sketches to remember the difference between the two types of mechanical advantage.
- By using a T chart students can list the differences between Ideal
Mechanical Advantage and Actual Mechanical Advantage. Shown is an
example of how you could use a T-Chart with the reading "MECHANICAL
ADVANTAGE":
Reading Support:
- There are three readings to support students in this lesson. The first reading "Mechanical Advantage" describes and gives examples of ideal and actual mechanical advantage.
- The second reading, “Secret Wheelbarrow Technology” discusses how the wheelbarrow is a second class lever. Examples of how the wheelbarrow was used historically and more current uses are discussed.
- The third reading, “More Simple Machines: the Wedge, Screw and Wheel and Axle,” discusses the simple machines that are not investigated in this unit.
Math Support:
- Students may need a lot of support with the equations for calculating Actual and Ideal Mechanical Advantage.
- Support students with the meaning of their calculations. Give students example questions such as, “If the Ideal Mechanical Advantage of the ramp into the school is 3.2, how long would the ramp need to be if you needed to reach a height of 2 meters?”