Energy, Machines, and Motion
Part Two: Machines
Lesson 12: The Pulley
Students construct different pulley assemblies to lift a K’NEX™ sled a given distance. Students will then measure the effort force and effort distance of these different assemblies and calculate the amount of work needed to lift the sled. Students will refine their definitions of a machine.
Focus Question: How do pulleys work? Why are pulleys machines?
3. Lesson Set-up and Management
EALR 2: Inquiry
Core content: Questioning and Investigating
6-8 INQC Collecting, analyzing, and displaying data are essential aspects of all investigations.
EALR 3: Application
Core content: Science, Technology, and Solving Problems
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 that pulleys are simple machines.
- Students observe that a pulley makes work easier by changing the magnitude of the work, or the direction of the force required to do the work.
- Students learn that a simple machine reduces the effort force, but increases the effort distance to do work.
3. Lesson Set-Up and Management
Materials:
- Have a pulley system set up prior to Lesson 12. Students are instructed to use this model for setting up their pulleys.
- Students need to record the weight of the sled attached to the movable pulley and record this as their load force.
- The string attached to the pulley should be at least 2.0 meters long. If students don’t have enough string they can tie a piece on the end to extend the length.
- Measuring effort distance can be difficult. Consider using different colored markers to measure the effort distance as students test the three different types of pulleys. Having the different colored marks will make measurements easier for students.
- The pulley cart system can be awkward. The system will want to list from side to side occasionally and the strings will come out of the pulleys. Assign a student to keep the pulley system steady as the tests are being performed.
Student Management:
- Review with students the concepts of load force, load distance,
effort force and effort distance and how those will look with a
pulley. Consider using the diagram in the teacher’s edition to
illustrate this concept.
- After the Reflection Questions, students are asked to write their definition of a machine. Students sometimes list machines they are familiar with, refocus those students by asking for a definition of a machine. .
- Students remove the pulley system from the pegboard for Lesson 13. Store the pulley systems intact, the pulleys will be used again in Lesson 16.
- Give students assistance when working with their pulleys. They may
need suggestions of how to wrap the strings. The examples in the student
edition serve as a good example. Students will want to have this with
them near their pulley systems. Consider having students paste this
diagram into their notebooks.
Writing Support:
- In the Getting Started portion of Lesson 12 students give some information about what they think a pulley is and how pulleys help lift loads. Students input their ideas of the conditions that can affect how much a pulley can lift. These ideas are designed to bring out their conception of pulleys.
- Students use Student Sheet 12.1 for this lesson. Consider having students trim the data table and paste them into their notebooks.
- Consider having students chart the types of variables they are working with:
|
Controlled |
Manipulated |
Responding |
|
Same load (sled) |
Different pulley systems |
Effort Force Effort Distance Work |
- Students have experienced two types of machines, the incline plane and the pulley. Consider using a Box and T-chart to illustrate how the incline plane and the pulley systems are similar and how they are different.
Reading Support:
- “Uses of Pulleys” gives students ideas about the use of pulleys before the investigation.
- “Going Up” tells the story of the development of safe public passenger elevators and how they have changed modern life.
Math Support:
- With a single fixed pulley the load force and load distance does not change from simply lifting the load the same distance. The work appears easier because you are pulling down rather than pulling up. Talk to students about why the data is the same, but it will “feel easier”.
- Students gather data for effort force and effort distance to calculate the work done to lift the sled. The work should be about the same with each pulley, yet small differences in data collection may appear. Talk about the slight differences in number with your students.