Drexel-SDP GK-12 ACTIVITY

Activity Template Subject Area(s) Data analysis & probability, measurement, number & operations, physical science, science & technology Associated Unit Simple Machines Associated Lesson Levers Activity Title

“Level with me” Grade Level 6th-8th Time Required 2 class periods Group Size 3 students per group Expendable Cost per Group US $10 Summary Students will learn how to identify and classify lever systems in the human body. Students will build a first class lever and then test the relationship between force and distance when calculating work. Students will also graph their results to find where they should place their effort on the lever to accomplish the most work.

Engineering Connection Engineers must understand the concept of levers when designing new tools for people to use. They must know how to calculate work in order to properly design the machines. Biomedical engineers must also understand levers in the human body as they design new hip replacements and prosthetics. Keywords Simple machines, levers, work, power, fulcrum, effort, and resistance Educational Standards • Science: 3.4.10.C • Math 2.2.8.A • Math: 2.6.5.A • •

Math: 2.7.8. B Math: 2.8.3.G, H

Pre-Requisite Knowledge • Recognize the different classes of levers • Understanding effort, resistance and fulcrum as it pertains to levers • Making a bar graph Learning Objectives After this lesson, students should be able to: • Recognize the three different types of levers in the human body. • Calculate the amount of work needed to lift a weight on a lever. • Recognize the relationship between force and distance on a lever system. • Establish the location of where they should put the weight on a lever to achieve the most work Materials List Each group needs: • PVC pipe • 4 PVC pipe 3-way joints • Metric ruler • Rubber Bands • Spring scale • Calculators • 50 gram weight • Graph Paper Introduction / Motivation The easiest way to relate levers to students is to begin talking about a seesaw. Ask students if they have ever been on a seesaw and if they can explain how it works. Most

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of them know from experience that pushing on the end of the seat will cause the other person to easily fly up in the air. Another way to introduce the topic of levers is to talk about athletes who play baseball or tennis. When a baseball player swings the bat and hits the ball furthest away from his hands he gets the most power, sometimes even leading to a home run. The same is true for tennis players who when serving the ball get an incredible amount of power by fully extending their body. The effort comes from all of their muscles, the fulcrum is their swinging shoulder, and the resistance is the ball striking the racket. The large distance between the shoulder and the racket or bat make it easier for an athlete to not have to use that much force and still perform a lot of work, leading to long hits and serves over 100 miles per hour. Students will be interested after watching a couple of videos of athletes in action. Vocabulary / Definitions Word Definition Lever One of the simple machines which allows humans to move heavy objects by applying a force on one end Fulcrum The point on which a lever rests Effort A force exerted by a machine or by the muscles in humans Resistance The opposition to a force such as the weight of an object Flexion The bending of a limb or joint (arm or leg) Extension The opposite movement of flexion of a joint or limb (arm or leg) Forearm The part of the arm from the elbow to the wrist Bicep The muscle in the upper arm facing up which allows flexion of the forearm Tricep The muscle in the upper arm facing down which allows extension of the forearm Joint A point in the body where two bones connect allowing movement Work A quantity in physics that relates the amount of force over a certain distance. Power Another quantity in physics that relates the amount of work done in a certain amount of time. Procedure Background This activity reinforces previous lessons on levers by extending it to the human body. The students should already know that the lever is a type of a simple machine composed of a fulcrum, resistance and an effort. By applying effort on one side of the lever the resistance is easily moved. In the real world examples of levers include a hammer, scissors, a wheelbarrow or a fishing rod. These tools help people accomplish their everyday tasks. Humans possess a variety of body parts that behave as levers including the elbow joint, the knee and the neck. The neck acts as a pivot (fulcrum) for the head, which supports the weight of the head (resistance) and the neck muscles do the effort. This represents a first class lever. The second class lever can be represented by the lower leg with the fulcrum at the knee, the 3

effort at the calf muscles and the resistance at the foot. The motion of lifting the forearm can represent a third class lever. The fulcrum is at the elbow, the effort is at the biceps and then the hand holds the resistance (Figure 1).

Figure 1: Top left picture shows the head and neck representing a first class lever. The top right picture shows a second-class lever in the lower leg. The bottom picture is a third class lever representation of the forearm.

Before the Activity • Review work (Force x Distance) equation with the students. • Explain the meaning of work in terms of physics. Students will often think of a job or their homework. They will relate it better to power so it is important that they understand the difference. • Cut PVC pipes into 7 parts each 4 inches in length • Make copies of worksheet • Make sure the spring scale and the 50 gram weight have hooks on them so they can be tied to the ruler With the Students First, have students construct the fulcrum with the PVC pipe. 1. Use 3 4” PVC pipes and one 3-way connector to make a T shape part. Repeat so you will have two T-shaped parts. Put another connector piece on the vertical ends

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of the T-shaped parts. Connect the two free connectors with the last 4” PVC pipe and now you will have a fulcrum (Figure 2).

Figure 2: Image of fulcrum made out of PVC for a 1st class lever.

2. Place the metric ruler on top of the fulcrum and secure it with a rubber band. 3. Place the spring scale on one end of the ruler and secure it with a rubber band. 4. Place the 50 gram weight on the other side of the ruler and secure it with a rubber band. Record the spot of the weight on the worksheet 5. Pull on the spring scale until the ruler is level. Record the force on the spring scale on the worksheet (Table 1). 6. Calculate the work needed to level the weight using the following formula: W=F*D Where W is the work required to level the weight in Newtons-meters, F is the force on the spring scale needed to keep the lever level in Newtons, and D is the distance between the weight and the spring scale in meters. If you measured your distance on the ruler in centimeters then remember to divide by 100 to make sure you are in the right units. W = (F * D) / 100 7. Move the weight to a couple of different locations on the ruler and repeat steps 4 – 6. 8. Make a bar graph of your results. Distance should be on the x-axis and work should be on the y-axis.

Table 1: Work done by the lever table. Trial

Weight Position (cm)

Spring Scale Position (cm)

Distance (cm)

Force (N)

Work (N-m)

5

1

2

48

2

2

47

3

2

46

4

2

45

5

2

44

6

2

43

7

2

42

8

2

41

9

2

40

10

2

39

11

2

38

12

2

37

13

2

36

14

2

35

15

2

34

Troubleshooting Tips The table has some starting values on it just because this would give the students some structure of where to place their weights and spring scale. However, they should be encouraged to try different locations if time permits.

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Investigating Questions 1. Which part of the lever served as the resistance, effort and fulcrum? 2. What class of lever does this represent? 3. Does it make a difference where you put the weight on the lever? In relation to the fulcrum where is it easier to lift the weight? 4. What is the most work that your lever achieved during the activity? Assessment Pre-Activity Assessment Title: Class discussion Before starting the activity ask the students how they would lift a heavy box using a lever. Ask the students if it matters where they push on the lever. Ask the students where they would put the fulcrum to make it easier. Ask the students if it matters how long the lever is. Activity Embedded Assessment Title: Work done by the lever table During the activity the students have to record the position of the weight and the spring scale and the force on the spring scale needed to make the lever level. Then the students have to calculate the work done by the lever and then graph their results. By completing the table and graph during the activity one can gauge the students’ progress. Post-Activity Assessment Title: Class analysis of charts After the students finish their bar charts the instructor will lead a class discussion on the results of the charts. Students must interpret their charts to find the best location to place the weight. Students should be able to answer questions about how distance affects the amount of force one has to apply to lift the object. The most efficient place to put the weight will have the largest distance consequently requiring the smallest amount of force. Students should now realize that a lever can significantly decrease the amount of effort needed to accomplish a task. Activity Scaling • For lower grades, use the chart as is. The location of the weight and the spring scale are predetermined so the students can move through the activity quickly. • For upper grades, the students can choose where to place the weight and the spring scale. They can also move the location of the fulcrum to simulate different classes of levers. References Figure 1 obtained from www.teachhealthk-12.uthscsa.edu. Teacher Enrichment Initiatives - Levers Unit: Lesson 3 Levers in the Body: They are not what you might think!

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Owner Drexel University GK-12 Program Contributors Mr Manuel Figueroa, PhD Candidate, School of Biomedical Engineering, Drexel University Ms Evelyn Cruz, Robotics Technology Teacher, Roberto Clemente Middle School, School District of Philadelphia Copyright Copyright 2008 Drexel University GK-12 Program. Reproduction permission is granted for non-profit educational use.

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