# Flinn PSWorks™ Lever Arm

## Student Laboratory Kit

### Materials Included In Kit

PSWorks™ Lever Arm
Screw

Paper clip, large (optional)
PSWorks™ Support Stand
Spring scale, measured in Newtons
String, thin
Weight hanger
Weights, slotted or hooked, set

### Prelab Preparation

Assembly Secure the Lever Arm to the PSWorks™ Support Stand using the screw and knob with threaded insert as shown in Figure 5.

{13334_Prepration_Figure_5}

### Safety Precautions

These laboratory activities are considered safe. Follow all normal laboratory safety rules.

### Disposal

All materials are reusable and require no disposal procedures.

### Teacher Tips

• Enough materials are provided in this kit for one group of 2–4 students. The laboratory activity and its discussion will likely require two 50-minute class periods.
• If slotted weight hangers are not the appropriate size, string hangers can be made (see Figures 6–8).
{13334_Tips_Figure_6}
{13334_Tips_Figure_7}
{13334_Tips_Figure_8}
• In addition, string loops can be made to slide over the lever arm so that balance can be “dialed in” for different masses (see Figure 9).
{13334_Tips_Figure_9_Alternate “dial in” method}
• Spring scales are designed to be held vertically with the mass hanging down. When a spring scale is pulled down, inaccurate measurements will result (due to unaccounted-for mass in the spring scale). Therefore, for Lever Type I, a string and pulley system may be used to redirect the downward pulling force to a lifting force. Students should use their pencils and string to redirect the downward force.
• 1000 g/10 N spring scales and 500-g masses work well for this activity.
• Advise students not to exceed the limit of the spring scale. If this should occur, students should obtain different spring scales or masses.
• Since the fulcrum is always at the center of mass of the lever arm, the mass of the lever arm will not contribute to the mass of the balanced system.

### Science & Engineering Practices

Developing and using models
Planning and carrying out investigations
Analyzing and interpreting data
Using mathematics and computational thinking
Constructing explanations and designing solutions

### Disciplinary Core Ideas

MS-PS2.A: Forces and Motion
HS-PS2.A: Forces and Motion

### Crosscutting Concepts

Systems and system models
Stability and change
Structure and function

### Performance Expectations

HS-PS3-2: Develop and use models to illustrate that energy at the macroscopic scale can be accounted for as a combination of energy associated with the motion of particles (objects) and energy associated with the relative position of particles (objects).

### Sample Data

Lever Type I Worksheet

{13334_Data_Table_1}

*Load is equal to the weight of the slotted masses. W = mg, where (0.1 kg)(9.8 m/s2) = 0.98 N ≈ 1 N.

Lever Type II Worksheet
{13334_Data_Table_2}

*Load is equal to the weight of the slotted masses. W = mg, where (0.1 kg)(9.8 m/s2) = 0.98 N ≈ 1 N.

Lever Type III Worksheet
{13334_Data_Table_3}

*Load is equal to the weight of the slotted masses. W = mg, where (0.1 kg)(9.8 m/s2) = 0.98 N ≈ 1 N.

Lever Type I Worksheet

1. In a Type I Lever, where is the fulcrum when the force and load are equal?
The fulcrum is equidistant between the force and load.
2. In a Type I Lever, what happens to the force required to lift a load as the load gets closer to the fulcrum? What happens to the mechanical advantage?
The force required to lift the load decreases and the mechanical advantage increases.
3. When the load is very close to the fulcrum and the force is far from the fulcrum, how does the distance the force moves compare to the distance the load moves?
The load moves a very short distance compared to the lever at the point of the force.
1. Lever Type I system would be good for moving a heavy object a small distance with less force required than the load.
True. The mechanical advantage is large when the fulcrum is close to the load.
2. Lever Type I system would be good for moving an object with great speed.
False. The load moves very little distance compared to the force.
3. A shovel is an example of a Lever Type I.
If the arm positioned in the middle of the shovel is used as a fulcrum, it can be a Lever Type I. The arm positioned at the end of a shovel can be used as a fulcrum and then the shovel becomes a Lever Type III.
Lever Type II Worksheet
1. Where would you place a load with this lever system to spend the least force to lift the load?
When the load is closest to the fulcrum, the least force is required to lift the load.
2. Would Lever Type II be a good system for lifting a heavy load with minimal force? Explain.
Yes. The lever is very capable of having a high mechanical advantage. Getting the actual lever under the load can be a problem.
3. Would Lever Type II be a good system for moving a load a long distance? Explain.
No. When the load is close to the fulcrum, the force moves a great distance while the load hardly moves any distance. The lever can have a good mechanical advantage, but has no speed or distance.
4. Think of at least one common item that illustrates a Lever Type II system and explain how it works. What are the advantages and disadvantages of using the item in doing work?
A wheelbarrow is a Type II lever system. Its good mechanical advantage allows lifting a heavy load with little relative force. The load, however, is not lifted very high off the ground if this were desired.
Lever Type III Worksheet
1. What happens to the force required to lift the load as the force gets further from the load?
The force required to lift the load increases.
2. What happens to the mechanical advantage as the force gets closer to the fulcrum?
The mechanical advantage decreases as the force gets closer to the fulcrum.
3. When the force is close to the fulcrum and a load is lifted, how does the distance the force moves compare to the distance the load moves? When might such an arrangement be advantageous?
The distance the load moves is much greater than the distance the force moves. Such an arrangement can use this distance travel to gain speed.

For each diagram, determine what lever type is illustrated and how the lever system is advantageous.

# Flinn PSWORKS Lever Arm

### Introduction

A wheelbarrow, a shovel, a hammer and nearly all tools are examples of lever systems in action. We utilize levers every day and have numerous examples in our own bodies. How do these levers work and how do they provide a mechanical advantage?

• Force
• Fulcrum
• Lever types

### Background

Levers are rigid objects, usually in the shape of a bar, that can turn on one point or axis. This point is called the fulcrum in the lever system. A lever is used for the transfer and modification of force and motion. The movement of objects can be made faster/slower, longer/shorter or easier/harder and can occur in various patterns. In a lever system, the lever itself is always rigid—like a bar, rod, plank or other rigid object. The load is whatever is being moved—a rock, a load in a wheelbarrow or other heavy object. The force is anything capable of doing mechanical work; it may be a spring, a motor, a jet, a person or any other item that can exert a force on the lever itself.

Lever systems in action are useful in gaining speed, distance, precision, or mechanical advantage. Mechanical advantage is defined as the ratio of force output to the force applied. Each lever system has its own unique properties and has tradeoffs between mechanical advantage and other properties. In general, there is a reverse relationship between mechanical advantage and both the amount and speed of movement, but there is no necessary relationship to precision.

The three basic lever types are diagramed in Figure 1. They are arbitrarily called Types I, II and III. Some texts call them A, B and C.

{13334_Background_Figure_1_Lever types}

### Materials

Paper clips, large (optional)
PSWorks™ Lever Arm
PSWorks Support Stand
Screw
Spring scale, measured in Newtons
String, thin
Weight hanger
Weights, slotted or hooked, set

### Safety Precautions

These laboratory activities are considered safe. Follow all normal laboratory safety guidelines.

### Procedure

Lever Type I: Fulcrum Between the Force and Load

1. Use the lever materials to set up a Type I lever system like that shown in Figure 2.
{13334_Procedure_Figure_2_Lever type I}
2. Use slotted weights to place a load in or near the outside hole of the lever arm. Be sure to hold the lever in place while adding the slotted weights.
3. Place the hook from the spring scale in the outside hole on the opposite end of the lever arm. The spring scale should hang down. Use a spring scale to measure the force needed to hold the lever system in balance (level). Record the weight of the load and the force needed to keep the load balanced in the Lever Type I Worksheet.
4. Hold the lever arm and move the load to the middle hole of the lever arm. Measure and record the force required to hold the load at this position.
5. Repeat step 4 for the inner hole of the lever arm. Record the force measurement in the worksheet.
6. Record the distances Df and Dl along with the force measurements for each load position on the Lever Type I Worksheet.
7. Calculate the mechanical advantage for each position tested and record the calculations on the worksheet.
{13334_Procedure_Equation_1}
8. Answer the questions on the Lever Type I Worksheet.
Lever Type II: Load Between the Fulcrum and Force
1. Use the lever materials to set up a Type II lever system like that shown in Figure 3.
{13334_Procedure_Figure_3_Lever type II}
2. Place the slotted weights in the interior hole and the spring scale in the outside hole on the same end. Be sure to hold the lever in place while adding the slotted weights.
3. Use a spring scale to measure the force needed to hold the lever system in balance. Record the weight of the load and the force needed to keep the load balanced in the Lever Type II Worksheet.
4. Move the load to the middle position along the lever arm. Measure and record the force required to hold the load level at this position.
5. Repeat step 4 for the outer hole of the lever arm (the same hole that the spring scale is attached). Record the force measurement in the worksheet.
6. Record the distances Df and Dl along with the force measurements for each load position on the Lever Type II Worksheet.
7. Calculate the mechanical advantage for each position tested and record the calculations on the worksheet.
8. Answer the questions on the Lever Type II Worksheet.
Lever Type III: Force Between the Fulcrum and Load
1. Use the lever materials to set up a Type III lever system like that shown in Figure 4.
{13334_Procedure_Figure_4_Lever type III}
2. Use slotted weights to place a load in the outside hole of the lever arm and the spring scale in the interior hole on the same end. Be sure to hold the lever in place while adding the slotted weights.
3. Use a spring scale to measure the force needed to hold the lever system in balance. Record the weight of the load and the force needed to keep the load balanced in the Lever Type III Worksheet.
4. Move the spring scale to the middle hole of the lever arm. Measure and record the force required to hold the load level at this position.
5. Repeat step 4 for the outer hole of the lever arm (the same hole where the load is hanging). Record the force measurement in the worksheet.
6. Record the distances and force measurements on the Lever Type III Worksheet.
7. Calculate the mechanical advantage for each position tested and record the calculations on the worksheet.
8. Answer the questions on the Lever Type III Worksheet.

### Student Worksheet PDF

13334_Student1.pdf

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