Investigation 2 – PreLab
Automobile engineers use a variety of simple machines to create cars. Cars are actually considered complex machines because they have motors and are composed of several simple machines to help make them run.
This Investigation is designed to help them to answer the following Focus Questions:
- How can simple machines change the force needed to lift a load?
- How does the relationship between the fulcrum, effort, and load affect the force needed to lift a load?
- How does mechanical advantage relate to effort and load forces and the lengths of effort and load arms?
Note: These questions are located in your SDR at the beginning and end of the Investigation.
As a class, read the Background(s) in the Investigation. When finished, discuss the following concepts as a class:
- A lever is another example of a simple machine.
- Examples of levers include scissors, see-saws, and wheelbarrows.
- Like pulleys, levers may make a task “feel easier.”
- Three types, or classes, of levers exist: first-class, second-class, and third-class levers.
- All levers consist of three parts: the load arm, the effort arm, and the fulcrum.
- In a first-class lever, the fulcrum is in the middle and the load and effort are on opposite sides of the fulcrum.
- Mechanical advantage describes the relationship between the effort force or force needed to lift the load and the force of gravity on the load, or the load force.
- Mechanical advantage can be calculated by comparing the effort arm length and load arm length using the following equation:
Mechanical Advantage = Effort Arm Length ÷ Load Arm Length
- A second-class lever is a lever in which the fulcrum is on one end of the arm, the effort is on the other end, and the load is between the effort and fulcrum.
LEARN THE LabLearner LINGO
- effort arm
- load arm
Note: Definitions of these terms can be found on the Introduction page to the CELL.
Note: Additional words may be bolded within the Background(s). These words are not Key Terms and are strictly emphasized for exposure at this time.
SET FOR SUCCESS
- Summarize to yourself or as a class what you learned about effort force, load force, work, and mechanical advantage in a single-pulley system.
Note: In a single-pulley system, the magnitude of the effort force is equal to the load force, and the work done on the load distance is equal to the work done on the effort distance. A single pulley system offers a mechanical advantage of 1 because there is no difference between the effort and load forces.
- Summarize what you learned about effort force, load force, work, and mechanical advantage in a two-pulley system.
Note: In a two-pulley system, the effort force is one half of the load force, but the work done on the effort distance was equal to the work done on the load distance. A two-pulley system offers a mechanical advantage of 2 because the effort force is one-half the magnitude of the load force.
- Remember that the work done on the effort distances were the same for both pulley systems. How this can be true if the effort force in the single-pulley system was different from the effort force in the two-pulley system?
Note: Work is calculated as force times distance. The effort force in the two-pulley system was one-half the effort force of the single pulley system. However, the distance over which the effort force was applied in the two-pulley system was double the distance over which the effort force was applied in the single-pulley system. When work is calculated, the difference in the two effort forces is canceled out by the difference in the effort distances; thus, the work done on the effort distance for both pulley systems was the same. The following equation illustrates this mathematically:
- Complete the Recall section in your SDR.
- What are some everyday examples of levers? How do they differ from one another?
- What are the different types of levers?
- Do all levers give the same mechanical advantage?
- How is energy conserved when using simple machines?
- Play the video below. Remember to follow along with your SDR and make any notes that you think might be helpful.
- After the video, divide into lab groups to discuss strategy for the lab. For example, you may assign certain group members to perform specific functions during the lab.
Note: The purpose of the video is to allow you to anticipate the laboratory experience you will soon encounter. You should leave this PreLab session with a firm idea of what to expect and how to perform in the lab.
Note: Homework is posted below the video.
You should review the Investigation and video in preparation for the Lab.