using a model of the human arm, students will be able to...

Positively Aging®/M.O.R.E.2007©The University of Texas Health Science Center at San Antonio

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Levers in the Body:They Are Not What You Might Think!Activities 3A, B, C, D, EActivity Objectives:Using a model of the human arm, students will be able to:

u Investigate lever systems in the human bodyu Observe how muscles and bones work together to move joints u Compare arm anatomy to modelu Explain that muscles must pull against the weight of various

body segments (resistance)u Distinguish between joint flexion and extensionu Observe that muscles can work only by pulling (contracting)u Graph and analyze results

Activity Description:Students will be surprised to learn that the levers in

their arm don’t behave as expected! They will use a model of the human arm, including an artistically modified scapula, humerus, radius and ulna. After measuring the weight of the forearm on their model with a spring scale, they will assemble the bones so that the elbow joint is moveable. Once students have assembled the model, they will attach string “biceps and triceps muscles” to the model at origin points labeled on the model. An approximation of the actual insertion point will be labeled on the model and the other end of the string “muscle” attached to that location. The student will then investigate how the biceps muscle operates the joint as a lever system, exploring angles and the resistanceand effort forces. Next, students will move the insertion point of thestring muscle to examine how the lever system changes. Both the tricepsand biceps will be studied in this part of the activity. Finally, using bodysegment weight percentages, students will relate their findings to theirown bodies.

Activity Background:As students discovered in the previous activity, “Just a Little Bit of Effort:Exploring Levers”, there are three classes of levers; first, second and thirdclass. The classification of levers is based upon the relative position ofthe Fulcrum (F), Effort (E) and Resistance (R). *(Resistance is often calledload (L)). Lever systems are important to human movement and arefound throughout the human body. The field of study that applies theprinciples of mechanics and anatomy to human movement is calledkinesiology (ki`neesee'âlujee). Before moving on, a cautionary state-ment is necessary. There is a significant amount of disagreement in theprofessional literature about the classification of lever systems in the

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LESSON 3 ACTIVITY 3A, B,

C, D, E

body. Human joints are complex, often incorporating many muscle connections and ligaments that allow a joint to function in several waysand creating complex sets of forces in the joint lever system. This com-plexity makes it difficult definitively classify joints as one type of lever oranother. All forces involved in moving a joint must be carefully definedand even experts in the field cannot always agree. This disclaimershould be carefully explained to students.

Just as the levers already studied, levers in the human body consist of arigid bar (bone), a fulcrum (joint), an effort force (pull of muscle onbone) and a resistance (load) force (weight of the body part beingmoved – this may include weight being held). An example is the elbowjoint, operated by the biceps and triceps muscles. The elbow is a com-plex joint held together by strong connective tissue which forms liga-ments. Supporting muscles, ligaments and the shape of the bones them-selves help to keep the bones of the joint from sliding sideways duringmovement. The position of the connection between muscle and bonecan alter the amount of rotation and speed with which joint moves.Speed is produced at a cost; reduction of power in the joint.

An example of a first class lever in the body includes the splenius muscleacting to balance head on atlanto-occipital joint. This lever allows us to tilt our head back. Figure 1, First Class Lever in the Body. It is important to note that there are few first class levers in the human body.

Figure 1 First Class Lever in BodyVery few, if any, second class levers are found in the body - rising on thetoe is identified and often disputed as a second class lever. The humanbody is not designed to apply a large force in a lever system, as occurs in a second class lever. Please note that many materials designed for students make definitive statements that rising on the toe is a second classlever – all experts do not agree on this point!!

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EFFORTRESISTANCE(Load)

FULCRUM

EFFORTMuscles at back

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FULCRUMAtlanto-occipital

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RESISTANCE(Load)-

Front of skull


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Third Class levers are the most common type of lever in the body –almost all movable joints function as third class levers. Examples includethe Biceps muscle moving the forearm. Students will be surprised todiscover that third class levers actually operate at a mechanical disad-vantage, in that more effort must be applied to overcome the resis-tance. Be sure to explain this carefully when you “process out” the activ-ity. The advantage of this design comes from the speed at which jointscan rotate. The fact that most levers in the human body function in thismanner indicates that our bodies are designed for speed over strength.

Figure 2 Third Class Lever in Body

Activity Materials: (per group)• Pattern for arm model • Stiff cardboard for arm model (note: more permanent models can

be made with wood*)• 1 1 N (100g) hanging weight• 1 1/4” X 3/4” bolt with wing nut (if using wooden models)• 1” diameter plastic pulley• Heavy brads (if using cardboard models)• Rubber Cement or Craft Spray Adhesive (Liquid Nails® to attach

laminated pattern to wood))• Ring Stand• 10 N Spring scale• Single hole punch• String (2 colors)• 6 #216 screw eyes used to attach string to

wooden models (reduces friction)• Protractor• Ruler• Student Activity Page packet for each group• Student Data Page packet for each student

* 1 2’ X 4’ piece of 1/4” thick wood makes about 18 models

EFFORTContracting

Biceps

FULCRUMElbow


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Activity Management: Prior to doing the activity, compare parts of the model to parts of thearm (Figure 1).

Be sure to explain to students that there is a significant amount of disagreement among experts about the classification of lever systems inthe human body.

Ask the Industrial Technology class to cut the pattern pieces out of 1/4”wood for more durable models. You can glue laminated pattern piecesonto the wood for models you will be able to use year after year. A 2’ X 4’ sheet of wood makes about 18 models.

Some students may be sensitive about using their own weight for someof the calculations in this activity. These students can do the calculationsusing a body weight of 80 lbs.

Extension:1. Investigate the knee joint by identifying the forces involved in knee

flexion. Determine what type of lever system is represented by knee flexion. Examine knee extension to identify the forces and type of lever system.

2. Observe how the triceps muscle serves as an opposable muscle to operate the elbow joint.

3. Students can investigate the concept of torque as it applies to levers in the body.

References Used: Broer, MR. (1973) Efficiency of human movement (Third Edition).Philadelphia: W.B. Saunders Company.

Delezene, Lucas, Fellows Lesson Website:http://gk12.asu.edu/curriculum/life_science/levers_body/index.html

Gowitzke, BA & Milner, M. (1988). Scientific bases of human movement(Third Edition). Baltimore: Williams & Wilkins.

Gray, H. (1918). Anatomy of the human body (20th Edition). Philadelphia:Lea & Febiger.

Hamill, J. & Knutzen, KM. (2003). Biomechanical basis of human movement(Second Edition). New York: Lippincott Williams & Wilkins.

Inspiration SoftwareΤΜ, Inc. http://www.inspiration.com

Medline Plus Medical Dictionaryhttp://www.nlm.nih.gov/medlineplus/mplusdictionary.html

Plagenhoef S, Gaynor Evans F, and Abdelnour T. Anatomical data foranalyzing human motion. Res Quart Exerc Sport 54: 169-178, 1983

Zatsiorsky. V. (2002). Kinetics of human motion. Champaign, IL: Human Kinetics.

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Previous learningassumed:

Classes of levers, muscles and bones allow

movement of joints, familiarity with terms muscle,bone, ligament, tendon, joint

Relevant TEKS:6, 7, 8.2 Scientific processes. The student uses scientificinquiry methods during fieldand laboratory investigations.The student is expected to: (B) collect data by observing and measuring; (C) organize, analyze, makeinferences, and predict trendsfrom direct and indirect evidence; (D) communicate valid conclusions; and(E) construct graphs, tables,maps, and charts using toolsincluding computers to organize,examine, and evaluate data. 6, 7, 8.3 C) represent the naturalworld using models and identifytheir limitations7.4 (B) collect and analyze information to recognize patterns such as rates of change.7. 6 Science concepts. The student knows that there is arelationship between force andmotion. The student is expected to: (A) demonstrate basic relation-ships between force and motionusing simple machine(C) relate forces to basic process-es in living organisms includingthe flow of blood and the emer-gence of seedlings including pulleys and levers; 7. 9 Science concepts. The student knows the relationshipbetween structure and functionin living systems. The student isexpected to:(A) identify the systems of thehuman organism and describetheir functions

Activity “Administrivia”:

Intended Grade Level:

6-8Key Concepts:

Levers in the human body,opposable muscle pairs,

flexion & extension, using caution in the

application of mechanics tohuman movement

Process Skills utilized in lesson:

Observing, inferring, measuring, and

graphing

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Figure 5 Arm Model Pattern Pieces

LEGEND Wooden Paper

1/4”1/8”

Screw eye

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Positively Aging ®

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Positively Aging®/M. O. R. E. 2006©The University of Texas Health Science Center at San Antonio

Positively Aging ®

/M. O

. R. E.

2006 ©T

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Health Science C

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LESSON 3 ACTIVITY 3A

Levers in the Body: They Are Not What You Might Think!

Student Information Pages, Activities 3A, B, C, D, EIntroduction:Movement is all around us all the time! Just think how boring things would be if we couldn’t move and if things around us stayed the same. You have studied about movement and have learned about levers, but you may not know as much about how levers work in your body. In this activity, you will be able to use a model of thehuman arm to explore movement of your elbow joint by a lever system. Before you go anyfurther, take a minute to move your elbow joint; flex and extend the joint. What observationscan you make about the way your elbow works?

Background:Actually your muscles, bones, ligaments and tendons come together to form complex joints. Joints in your body are places where two or more bones come together and are held together by tough connective tissue called ligaments. Muscles are attached to the bones with tough connective tissue called tendons. The muscles, tendons, ligaments and the shapes of the bones themselves allow movement of joints in specific ways and help prevent undesirable slipping and sliding.

Remember from the previous activity, “Just a Little Bit of Effort: Exploring Levers”, there arethree classes of levers; first, second and third class. The classification of levers is based uponthe relative position of the Fulcrum (F), Effort (E) and Resistance (R). *(Resistance is oftencalled load (L)). Lever systems are important to human movement and are found through-out the human body. The field of study that applies the principles of mechanics and anato-my to human movement is called kinesiology (ki`neesee'âlujee). Before moving on, a cau-tionary statement is necessary. There is a significant amount of disagreement among expertsabout the classification of lever systems in the body. Human joints are complex, often includ-ing many muscle connections and ligaments that allow a joint to function in several waysand creating complex sets of forces in the joint lever system. This complexity makes it diffi-cult to classify joints as one type of lever or another. All forces involved in moving a joint mustbe carefully defined and even experts in the field cannot always agree.

Just as the levers you already studied, levers in the human bodyconsist of a rigid bar (bone), a fulcrum (joint), an effort

force (pull of muscle on bone) and a resistance (load)force (weight of the body part being moved – this

may include weight being held). An example is the elbow joint, operated by the biceps and triceps muscles; see Figure 1, Lever System in the Body.


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Figure 1 Lever System in the Body

FULCRUMElbow

EFFORTContracting

tricepsRESISTANCE

Weight of forearm

An example of a first class lever in the body includes the muscles acting to balance head on neck joint. This lever allows us to tilt our head back. See Figure 2, First Class Lever in the Body. It is important to note that there are few first class levers in the human body.

Figure 2 First Class Lever in BodyVery few, if any, second class levers are found in the body - rising on the toe is identified and often disputed as a second class lever. The human body is not designed to apply a large force in a lever system, as occurs in a second class lever. Please note that many materialsdesigned for students state that rising on the toe is a second class lever – not all experts agreeon this point!!

Third Class levers are the most common type of lever in the body – almost all movable joints function as third class levers. Examples include the biceps muscle moving forearm; see Figure 3, Third Class Lever in the Body.

t

EFFORTRESISTANCE(Load)

FULCRUM

EFFORTMuscles at back

of head

FULCRUMAtlanto-occipital

joint cranium

face

RESISTANCE(Load)-

Front of skull


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EFFORTContracting

Biceps

FULCRUMElbow

RESISTANCEWeight of forearm

Figure 3 Third Class Lever in Body


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Activity Materials: (per group)• Pattern for arm model • Stiff cardboard for arm model (note: more permanent models can be

made with wood*)• 1 1 N (100g) hanging weight• 1 1/4” X 3/4” bolt with wing nut (if using wooden models)• 1” diameter plastic pulley• Heavy brads (if using cardboard models)• Rubber Cement or Craft Spray Adhesive (Liquid Nails® for

attaching laminated pattern to wood)• Ring Stand• 10 N Spring scale• Single hole punch• String (2 colors)• 6 #216 screw eyes used to attach string to wooden models (reduces friction)• Protractor• Ruler• Student Activity Page packet for each group• Student Data Page packet for each student

* 1 2’ X 4’ piece of 1/4” thick wood makes about 18 models

Instructions: (Read each instruction and check off each step as it is completed.)

p 1. For wooden models, trace the pattern pieces found in Figure 5 Arm Model Pattern Pieces (page 10) onto 1/4” plywood and cut out using a jig saw. Smooth the cut edges with sandpaper. Using Liquid Nails® adhesive, glue laminated and trimmed pattern pieces to the wooden cut-outs.

p 2. For cardboard models, glue the page with the pattern pieces, Figure 5 Arm Model Pattern Pieces to rigid cardboard or tag board. There is a pattern piece for the scapula (shoulder blade) and humerus (upper arm) and a pattern piece for the radiusand ulna (bones of the forearm).

p 3. Cut out each pattern piece. Since you are working in a group, have each student cut out a different pattern piece – this is good time management!

p 4. The pattern pieces include large, solid dots which should be punched out on card-board models or drilled out on wooden models (use a 1/8” drill bit). The elbow joint circle of cardboard models can be punched for the brad to be inserted. For wooden models, the hole marking the elbow joint must be drilled using the 1/8” bit to make a pilot hole and then with a 1/4” drill bit to finish the hole. Also on the pattern pieces are smaller, open circles which mark the locations for #216 screw eyes to be inserted. Find these locations and carefully insert the screw eyes. Refer to Figure 5 Arm Model Pattern Pieces for an abbreviated legend of these markings.

p 5. Attach the pattern pieces at the elbow joint using heavy brads for cardboard models or bolts with wing nuts for wooden models. The elbow joint should move freely after being assembled. The scapula and the shoulder joint will be immovable in this model to better isolate the elbow joint.

p 6. The protractor being used to measure the joint angle can be used separately or can be attached to the model. To attach the protractor to the model, find the center of the protractor straight edge and drill a 1/4”inch hole. Open the elbow joint brad on card board models or remove the wing nut from wooden models and place the newly drilled protractor hole over the brad or bolt. Close the brad or reattach the wing nut, depending upon which type of model you are making.

p 7. Attach a supporting piece of cardboard or wood to the scapula. This supporting piecewill be attached to the ring stand; see Figure 4 Setting up the Model. For wooden models, attach the arm model to a 2” x 2” piece of wood that is 12” long and is center drilled to fit your ring stand.

p 8. From this point forward, follow the instructions on your Student Data Page, filling in measurements and observations as you complete the activity.

Figure 4 Setting Up the Model


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Student Data Page 3B

Examining Joint Angle:Before starting, tighten the wing nut on the joint so the forearm will stay at a 90o angle. Remind students that the biceps muscle flexes the elbow joint.

p a. Run one end of the string through the Biceps Insertion Point A on the arm model (small screw eye) and make a large knot on the end of the string to keep it from passing through when the other end is pulled.

p b. Run the other end of the string through the Biceps Origin Point on the human arm model, and tie a loop into the end. Pull the string so it is taut, but does not move the lower arm. Use a fine tip marker (permanent) to mark off 1 cm intervals on the “biceps” string.

p c. Carefully pull the string (representing the pull exerted when the biceps muscle contracts) through the Biceps Origin Point so that exactly 1 cm of string is pulled through.

p d. Using the protractor, measure the angle of the elbow joint and record your measurement in Table 1, Joint Angle at Various Insertion Points under the column heading Biceps Insertion Point A Joint Angle.

p e. Repeat steps c and d for 2 cm, 3 cm, 4 cm and 5 cm.

p f. Next, you will see what happens to the joint if you change the insertion point of the Biceps muscle. Repeat steps a - e using Insertion Point B.

p g. Repeat step f using Insertion Point C.

p h. Use the graph paper included with this activity to make a line graph of the string shortening vs. joint angle. Use one color for Insertion Point A, a second color for Insertion Point B and a third color for Insertion Point C. Be sure to put a legend on your graph.

Table 1 Joint Angle at Various Insertion Points

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5 (Total) Angular Movement per cm string (Total : 5)

Length of StringPulled through

Biceps Origin Point(Cm)

Biceps Insertion Point A

Joint Angle

Biceps Insertion Point B

Joint Angle

Biceps Insertion Point C

Joint Angle


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LESSON 3 ACTIVITY 3B


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Student Name _______________________________________

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Processing Out:1. For each insertion point, what happened to the joint angle as the biceps muscle

(string) got shorter? ________________________________________________________________________________________________________________________________________________________________________________________________

2. How do the joint angles measured at Insertion Point A (represents the actual insertion point on your arm) compare to the joint angle measurements taken at Insertion Point B? _____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

3. Specifically, how did moving the insertion point of the muscle change the lever system that operates the elbow? _____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

4. When you pulled 2 cm of string through, why do you think the joint angles were different for insertion points A, B, and C? _____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

5. Do you think changing the insertion points made the lever system more efficient? Explain your answer. _____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

6. How would your arm function differently if it were designed so that your biceps muscle were attached to bone near your wrist? _____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

7. What conclusion(s) can you make from looking at your graph? ______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________


Student Data Page 3C

Measuring Forces:Before starting, tighten the wing nut on the joint so the forearm will stay at a 90o angle. Remind students that the biceps muscle flexes the elbow joint. Note: Biceps muscle is a flexor, which bends the elbow joint.

p a. Remember that Force = Mass x Acceleration of Gravity and that the weight of an object is a force. In the English System of Measurement, weight is measured in pounds and in the Metric System, weight can be measured in Newtons.

p b. Firmly attach the biceps string to the Biceps Insertion Point A and run it through theBiceps Origin Point as before (Do not tie the string to the Biceps Origin Point).

p c. Now, hang a 1 N weight from the screw eye at the end of the lower arm.

p d. Attach the spring scale to the loop at the end of the “Biceps” string passing through the Biceps Origin Point. Set the arm at a 90o angle and pull up on the spring balanceuntil the arm moves 30o upwards. Read the amount of force (Effort) in Newtons from the spring scale. Record this number in Table 1 Measuring Forces (Biceps).

p e. Next, you will move the Insertion point to see how the new location will affect the effort force. Repeat steps b – e for Insertion Point B.

p f. Repeat steps b – e for Insertion Point C.

p g. Make a bar graph of the Effort Force (N) at Various Insertion Points for the biceps muscle. Use one color for Insertion Point A, a second color for Insertion Point B and athird color for Insertion Point C. Be sure to put a legend on your graph.


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LESSON 3 ACTIVITY 3C


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Trial NumberEffort Force

Insertion Point A (N)

Effort Force Insertion Point B

(N)

Effort Force Insertion Point C

(N)

__________________________________________________________________

__________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

Table 1 Measuring Forces (Biceps)

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Processing Out:1. What part of the elbow lever system is the fulcrum?

________________________________________________________________________________________________________________________________

2. What part of the elbow lever system is the resistance force?________________________________________________________________________________________________________________________________

3. What part of the elbow lever system is the effort force? ______________________________________________________________________________

4. What happened to the amount of force required to move the forearm as the insertion point of the muscle was moved further from the joint? ____________________________________________________________________________________________________________________________________________________________

5. Looking at Table 1, Insertion Point A, how did the effort force compare to the resistance force (weight of the forearm + the 1 N weight)? ______________________________________________________________________________________________________________________________________________________________

6. The answer to question number 5 seems unexpected. Why do you think the joint is made so that it operates at such a disadvantage?______________________________________________________________________________________________________________________________________________________________

7. When the biceps (string) was moved from Insertion Point A to Insertion Point B, what happened to the amount of effort force?______________________________________________________________________________________________________________________________________________________________

8. Specifically, how did moving the insertion point further from the joint affect the lever?______________________________________________________________________________________________________________________________________________________________

9. Why do you think moving the insertion point affected the lever in the way you described in question 8?_____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

10. What conclusion can you make about forces in the elbow lever system from looking at your graph?____________________________________________________________________________________________________________________________________________________________________________________________________________


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LESSON 3 ACTIVITY 3D


Student Data Page Activity 3D

Examine Pulley System: TricepsBefore starting, tighten the wing nut on the joint until the forearm stays at 90o

on its own. Remind students that the triceps muscle extends the elbow joint. Note: The triceps is an extensor muscle, meaning that it straightens a joint.

p a. Remember that Force = Mass x Acceleration of Gravity and that the weight of an object is a force. In the English System of Measurement, weight is measured in pounds and in the Metric System, weight can be measured in Newtons.

p b. Firmly attach the triceps string to the Triceps Insertion Point A and run it through the Triceps Origin Point as before (Do not tie the string to the Triceps Origin Point).

p c. You will notice that when you pull on the String (triceps), it does not extend the arm of the model as it should since the triceps is an extensor muscle. This is an unexpected finding - What’s going on?

p d. The string representing the triceps crosses the pivot point of the joint, causing the force it exerts to bend the arm as the biceps muscle does. The line of force of the triceps cannot cross the pivot point and straighten the joint.

p e. A modification to the model can be made to simulate the anatomy of the elbow joint. Remove the wing nut and bolt, insert a small pulley between wooden upper arm and forearm, reinsert the bolt and tighten the wing nut. Run the string through the pulley, keeping it from crossing the pivot point. Another option is to insert screw eyes into the points around the elbow joint indicated on the paper and run the stringaround them, again keeping the string from crossing the pivot point. Observe what happens as you pull the “triceps” string and the pulley reverses the direction of pull.

p f. In the human body, tendon sheaths hold muscle tendons in place much as the pulley or screw eyes did on your model. They reverse the direction of pull and therefore do the same job as a simple pulley.

100 N

100 N100 N

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Processing Out:1. At first, the string representing the triceps muscle did not straighten the arm

as it should have. Why didn’t it work like the triceps muscle in your body?________________________________________________________________________________________________________________________________ ________________________________________________________________________________________________________________________________

2. What changes were made to the model to make it work correctly?___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

3. How do these changes represent the anatomy in the human body?___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

4. What is the purpose of a tendon sheath?___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

5. How is it similar to a simple pulley?___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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LESSON 3 ACTIVITY 3D


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LESSON 3 ACTIVITY 3E

Body Weight ________ lb x 4.45 N/lb = ________ N

Yikes


Student Data Page Activity 3E

Applying What You Learned to Your Own Body: The weight of your body segments provides resistance in human body lever systems.

p a. Using Table 4 Body Segment Weight Predictions, calculate the weight of each of your body segments and fill it in on Figure 1 The Segmented Phoon. (Note: if you do not wish to use your own body weight, you can do the calculations using an 80 pound body weight.)

p b. In order to use the Body Segment Weight Predictions, you must first calculate your body weight in Newtons. To convert body weight in pounds into body weight in Newtons, multiply Body weight in pounds by 4.45 N/lb. For example, if a person weighs 100 lbs, his/her body weight in Newtons (N) would be:

100 lbs x 4.45 N/lb = 445 N

( - the number looks large because we’re not used to seeing our body weight expressed in to Newtons)

p c. Write the correct numbers into Table 1 Calculating Your Body Segment Weights.

p d. Complete Table 1 Calculating Your Body Segment Weights by doing the calculations.

p e. Write the weight of each body segment into Figure 1 The Segmented Phoon.


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Table 1 Body Segment Weight Predictions

Body Segment % Body Weight (N)Males Females

Head & Neck 8.26 8.2Trunk 46.8 45.22Upper Arm 3.25 2.90Forearm 1.87 1.57Hand 0.65 0.50Thigh 10.50 11.75Lower leg 4.75 5.35Foot 1.43 1.33

_______________Trunk

Figure 1 Segmented Phoon

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___________Forearm

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Lower Leg

___________Foot

_____Hand

___________Head

& Neck

For more information about phoons, please seehttp://www.phoons.com/

Body Weight (N)


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Multiplied by %Body Weight

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of Body

Segment

Body Weight (N) Multiplied by % Body Weight*

Equals Weight ofBody Segment

Body Segment

body weight (N) X % body weight

= weight of body segment

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Table 5 Calculating Your Body Segment Weights

Head & NeckTrunkUpper ArmForearmHandThighLower legFoot

* This percentage comes from Table 4 Body Segment Weight Predictions Be sure to move the decimal point two places to the left before multiplying!

Processing Out:1. Looking at Figure 1 The Segmented Phoon, what is the resistance force

(weight of forearm and hand) in Newtons, of your elbow/biceps lever system? ________________________________________________________________

2. The lever system created by your elbow is a third class lever. It must pull approximately 8 times the weight of your arm in order for you to bend your elbow. Predict how much effort the biceps muscle in your arm might have to pull for you to bend your elbow. ______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

3. Look at Figure 1 The Segmented Phoon. What is the weight of your leg? (Be sure to add lower leg, thigh, and foot) _________________________________________________

4. If your thigh muscles operate a 3rd class lever that has a mechanical advantage of 1/10 (R/E) how much force (effort) must they use to lift your leg? __________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

5. Look at the image to the right and notice the size of the thigh muscle (quadriceps). Thinking about your experience with levers in the body, why do you think the thigh muscle (quadriceps) must be so strong? _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________


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Fulcrum

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using a model of the human arm, students will be able to...

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