Experiment
First-Class Levers
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A lever is a simple machine used to make work easier. It can help you move heavy objects by
increasing the force you exert. A lever consists of a long, rigid bar with a support that allows the
bar to pivot. The point where the bar pivots is the fulcrum. There are three classes of levers: first,
second, and third. A first-class lever looks like a seesaw. The effort (applied) force and resistance
force (load) are at opposite ends with the fulcrum somewhere in between. Crowbars and scissors
are examples of first-class levers. In a second-class lever, the effort force and the fulcrum are at
opposite ends with the load in between. Wheelbarrows and nutcrackers are examples of secondclass levers. When you do a pushup, your body is acting like a second-class lever with your toes
as the fulcrum helping to lift your entire weight with your arms. In a third-class lever, the effort
force is between the fulcrum and the load. Baseball bats, oars, and shovels are examples of thirdclass levers. Mechanical advantage (MA) is a value that tells the number of times a lever
increases your effort force. Actual mechanical advantage (AMA) includes friction losses, while
ideal mechanical advantage (IMA) does not. The difference between the ideal and actual
mechanical advantage is a measure of the lever’s efficiency. In this activity, you will study firstclass levers using a Force Sensor to measure the load and the effort force required to lift it. You
will then use this information to calculate the mechanical advantage of your lever.
Figure 1: Pulling a lever with the Dual-Range Force Sensor
OBJECTIVES
al
In this experiment, you will
Ev
• Use a Force Sensor and NXT to measure the effort force required to pull a lever.
• Compare actual mechanical advantage and ideal mechanical advantage.
• Make conclusions about levers.
MATERIALS
computer
LEGO NXT Intelligent Brick
MINDSTORMS Edu NXT 2 software
Vernier NXT Sensor Adapter
NXT Cable
STEM 2 with Vernier and LEGO MINDSTORMS NXT
Vernier Dual-Range Force Sensor
500 g mass
loop of string
meter stick
fulcrum
2-1
Experiment 2
PROCEDURE
1. Place a fulcrum near the edge of your lab table. Balance the middle of a meter stick on the
fulcrum as shown in Figure 1.
2. Prepare the NXT for data collection.
a.
b.
c.
d.
Set the switch on the Dual-Range Force Sensor to 10 N
Connect the Dual-Range Force Sensor to the Vernier NXT Sensor Adapter.
Connect the Adapter to Port 1 on the NXT using a LEGO NXT cable.
Make sure the NXT is connected to the computer (USB or Bluetooth) and turned on.
3. Launch NXT 2 Programming.
4. Prepare the program for force data collection.
a. Click the Go button next to Start New Program.
b. Drag a Vernier Sensor Block from the Sensor palette to the programming area.
c. In the configuration panel at the lower-left corner of the computer screen, select Force
(10 N) from the Sensor pull-down list.
d. You should see live sensor readings displayed in the configuration panel in the lower lefthand corner of the screen.
5. Hang the 500 g mass from the hook of the Force Sensor. The 500 g mass will be acting as the
resistance force in all three trials. Record the force reading in Table 1 under Resistance Force
(Fr) for Trials 1, 2 and 3.
6. Place the center of the 500 g mass on the meter stick at the 90 cm line (Dr = 40 cm).
7. Attach a loop of string to the Force Sensor and loop it over the meter stick at the 10 cm line
(De = 40 cm).
8. Pull down on the handle of the Force Sensor until the meter stick is balanced. Record the
force needed to balance the meter stick in Table 1. This is the effort force (Fe).
9. Slide the center of the 500 g mass to the 70 cm line (Dr = 20 cm). The position of the effort
force (the Force Sensor’s position) should not change. Repeat Step 8.
10. Now slide the center of the 500 g mass to the 60 cm line (Dr = 10 cm). The position of the
Force Sensor should not change. Repeat Step 8.
2-2
STEM 2 with Vernier and LEGO MINDSTORMS NXT
First-Class Levers
DATA
Table 1
Trial
Resistance
Distance, Dr
(cm)
1
40
40
2
20
40
3
10
40
Resistance
Force, Fr
(N)
Effort
Distance, De
(cm)
Effort
Force, Fe
(N)
PROCESSING THE DATA
1. Calculate the actual mechanical advantage for each of your three trials using the formula
AMA = Fr / Fe
where AMA = actual mechanical advantage, Fr = resistance force, and Fe = effort force.
Record your results in Table 2.
2. Calculate the ideal mechanical advantage for each of your three trials using the formula
IMA = De / Dr
where IMA = ideal mechanical advantage, De = effort distance, and Dr = resistance distance.
Record your results in Table 2.
3. Calculate the percent difference between IMA and AMA for each of your trials using the
formula
% Difference =
IMA − AMA
x 100
IMA
Record the results in Table 2.
Table 2
Trial
AMA
IMA
Percent Difference
1
2
3
4. What happened to the mechanical advantage as you shortened the resistance distance?
5. How did moving the resistance force closer to the fulcrum affect the effort needed to balance
it?
STEM 2 with Vernier and LEGO MINDSTORMS NXT
2-3
Experiment 2
6. What was the ideal mechanical advantage of the first lever you tested? Why would a lever
like this be used?
7. Are your values for percent difference between IMA and AMA large or small?
8. Describe some factors that might contribute to the difference between IMA and AMA in this
experiment.
EXTENSION
1. Design and perform an experiment to test either or both second-class and third-class levers.
(Reread the background information for a description of the setup.) Include a data table,
calculations, and conclusions.
2-4
STEM 2 with Vernier and LEGO MINDSTORMS NXT
Vernier Lab Safety Instructions Disclaimer
THIS IS AN EVALUATION COPY OF THE VERNIER STUDENT LAB.
This copy does not include:
z
Safety information
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Essential instructor background information
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Directions for preparing solutions
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Important tips for successfully doing these labs
The complete STEM 2 with Vernier and LEGO® MINDSTORMS® NXT lab manual includes
12 lab activities and eight projects as well as essential teacher information. The full lab book
is available for purchase at: http://www.vernier.com/cmat/stem2.html
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