Levers: How the Human Body Uses them to its Advantage

Goals:

• The students will synthesize the concept of levers and their corresponding terms by building all three classes of levers using the musculoskeletal system as their template.
• The students will be able to assimilate the concept of levers with human movement

Concepts:

• A lever is a rigid body that rotates around a pivot point and exerts force on an object preventing its tendency to rotate
• 1st class lever: effort and load are on opposite sides of the fulcrum; a small effort can be used to advantage over larger weight when using a larger lever arm
• 2nd class lever: effort and load are on the same side of the fulcrum with the effort acting through a longer moment arm than the load; a small effort can overcome a larger weight
• 3rd class lever: effort and load are on the same side of the fulcrum with the effort acting through a shorter moment arm than the load; more effort required but gains speed of movement of the weight
• The musculoskeletal system is a system of levers designed to allow human movement and work

Terms associated with levers:

• Fulcrum: the pivot point of a lever
• Effort: the force applied to a lever
• Resistive force, load or resistance: force that resists the motion of the lever
• Moment arm: the perpendicular distance from the line of action of the force of the fulcrum
• Mechanical advantage: ratio of output force : input force

Lesson Format:

• This is an interactive lecture.

Time Needed:

• Two and a half class periods

Materials:

• Something to use as a skeleton. I have resin skeletons from Anatomy in Clay, but you can use anything
• Clay
• Paper clips or dissection pins
• Small post-it notes or small pieces of paper and tape for labels

Concept Knowledge:

• Review basic musculoskeletal anatomy (e.g. two points of attachment, cross a joint, etc.)
• Point out parts of musculoskeletal anatomy that are the lever arm, fulcrum, force resistance/load, force effort/work, etc. as you do the lecture to tie in the lever concept with the human anatomy

Written exam (Acrobat (PDF) 203kB Jul27 07)
Lecture:
I will take some answers and introduce the concept of levers to help aid us in doing work. Next, I will go through what is a lever, the parts of a lever, and the three classes of levers.
Then I will introduce the concept that the musculoskeletal system is a system of levers designed to allow human movement and work and show them how this is by building all three classes of lever and identifying the parts of each lever:

• 1st class lever: Skull - extension against resistance with the spine as the fulcrum
• 2nd class lever: Gastrocnemius/Soleus - plantarflexion against resistance with the ball of the foot as the fulcrum
• 3rd class lever: Biceps—elbow flexion against resistance with the elbow as the fulcrum

Guided Practice:
The students will individually reinforce the lecture information by building the same muscles out of clay and identify the parts of the lever system by labeling them on a plastic skeleton. I will walk around and provide assistance. When they are finished they will remove the labels and quiz the person sitting next to them with 5 questions of their choice, correct the impromptu quiz, and then be quizzed by their partner.

Independent Practice:
For independent practice the students will partner up and build two examples of each type of lever on either/both the appendicular and axial skeleton (for a total of 6 levers). When this is completed they will study their levers and when they feel confident they will approach me to present their levers (each will present three) for a grade and then they will each be quizzed by me with random questions on any of the levers. Both partners receive the same grade for the presentations and the quiz. They must be finished with me 10 minutes before the end of the second class period or they receive zeros for the presentation and quiz.

Closure:
To close out this lesson the students will write out a list of activities and identify where the lever is in that activity. This will be done as a group with one piece of paper and the first person verbalizing the activity and the lever while writing down their answer. Then the paper is passed to the next person who does the same thing. This will go around the table three times and no activities may be repeated. Then each group will share two of its activities and as a class we will discuss their answers.

Exam:
There will be a paper/pencil exam during the first half of the third day. It will cover the lever terms and concepts along with some pictures of muscles and their attachments requiring students to identify the type of lever it represents and correctly labeling the parts of that lever.

**You can see an example of this type of test in the Attachments. It is not mine but one I found that I would adapt to my students since I believe this is intended for middle school students.

Tips:
Make sure that students work together on their levers and that they understand they are both responsible for their presentation and quiz grades. This way both people have motivation and a vested interest in learning the material.

Note: the muscles that they create do not have to be real muscles but they must meet the criteria of the lever class they are labeling it as. This reinforces the lever concept and allows them to think about how it works and would attach in order to work as the lever they want it to be. I like this aspect of the activity because it allows them to be creative and think outside the box rather than be confined to "anatomical structure" and be concerned about whether their origin and insertion are correct.

Informal assessments:

• Walking around during guided practice and giving pointers
• Student-to-student quizzes

Formal Assessments:

• Lever presentations
• Lever quiz on their models
• Exam (paper/pencil)

II.E.2 - Forces of Nature