Pulley. Design and Engineering. An Introduction to Simple Machines

Transcription

1 Design and Engineering An Introduction to Simple Machines Educational Objectives After this lesson, students should be able to understand and apply the following concepts: Basic elements of a pulley Transfer of motion from one direction to another Calculation of mechanical advantage Construction of a pulley system Conduct an authentic assessment of mathematical predictions and calculations Intrinsic value of pulleys and the ability to apply that knowledge to future applications and solutions Education Standards Next Generation Science Standards 3-5-ETS1-1 MS-ETS1-1 HS-ETS ETS1-2 MS-ETS1-2 HS-ETS ETS1-3 MS-ETS1-3 HS-ETS1-3 MS-ETS1-4 HS-ETS1-4 Common Core Standards W.5.7 RST WHST W.5.9 RST RST MP.2 RST RST MP.4 MP.5 SL.8.5 Standards for Technological Literacy 2.K K K K

2 Welcome Activity Information This design and engineering project is designed to introduce students to one of the six simple machines: the pulley. Students will learn how a pulley works by building one, applying the mathematics behind it, and learning key terms related to the subject matter. Classroom Management This activity packet should serve as a guide for teachers and students to learn about important concepts in design and engineering. Students can work in groups of up to four throughout this activity. Resources Each group of four students should use one Rokenbok SnapStack Module or one Rokenbok Advanced Projects Lab. Activity Time Minutes Table of Contents Simple Machines: Information Objectives... 1 Standards... 1 Activity Information... 2 Classroom Management... 2 Resources... 2 Activity Time... 2 Getting Started... 3 Building Basics... 4 s... 5 Science Concepts... 6 Technology and Engineering... 7 Build Plan: Math Concepts Design Challenge: Elevator System Design Process Design Reflection Presentation Assessment

3 Getting Started Introduction In order to be prepared to learn about the pulley, the following key terms have been provided below. These terms will be frequently used throughout the lesson. A bank of online key search terms have also been provided. Use a computer to research these terms as you progress through the lesson. Key Terms : Simple Machine: Effort: Resistance/Mass: Block and Tackle: A wheel and axle used in conjunction with a rope or cable that can use mechanical advantage to move heavy loads with minimal effort. A device that transmits or modifies force or motion. Force used to move an object over a distance. Force to overcome, object to be moved, otherwise known as load. A system of two or more pulleys with a rope or pulley threaded between them, usually used to lift or pull heavy loads. Online Key Search Terms Simple Machines Mechanical Advantage s Block and Tackle Wheel Radius Axle Radius Fixed Moveable Spring Scale Resources The Rokenbok SnapStack Module or Advanced Projects Lab can be used to complete the remainder of this lesson. SnapStack Module Advanced Projects Lab 3

4 Building Basics Building Basics with Rokenbok The following tips will be helpful when using the Rokenbok Student Design and Engineering System. Connecting/Separating ROK Blocks: ROK Blocks use a friction-fit, pyramid and opening system to connect. Simply press pyramids into openings to connect. To separate blocks, pull apart. Connecting/Separating Rokenbok Components Smaller Rokenbok components use a tab and opening system to connect. Angle one tab into the opening, and then snap into place. To separate, insert key into the engineered slot and twist. Snapping Across Openings The tabs on Rokenbok components can also be snapped across openings to provide structural support to a design. This will also allow certain designs to function correctly. Attaching String: In some instances, string may be needed in a design. Lay string across opening. Snap any Rokenbok component with tabs or pyramids into opening. Make sure tabs run perpendicular to string for a tight hold. Measuring: The outside dimensions of each Rokenbok connector block is 2cm 3. This means the length, depth, and height are all the same. To determine the size of a Rokenbok build in cm, simply count the number of openings and multiply by two. Repeat this process for length, depth and height. 2cm 2cm 2cm 3 Openings 9 Openings 18cm 6cm 4

5 s What is a? A pulley is a simple machine that helps make work easier. A pulley is basically a wheel and axle with a groove cut into the edge of the wheel to accept a rope or string. The pulley allows the rope to be attached to a load and transfers the upward motion of the load with a downward pull of the rope. Let s look at the basic parts of a pulley system. Parts of a Key Fixed Mount Axle Grooved Wheel Rope How Does a Work? The grooved wheel is attached to the axle with a key. This allows the wheel and the axle to move together on the pulley mount. The grooved wheel prevents the rope or string from slipping off. The rope must be under tension, or pulled tight in order for the pulley to work. When you pull on the rope of a pulley, it becomes tight and the effort of your pull is transferred through the pulley and down to the load. This tightness, or tension, allows you to lift a load more easily than just lifting the load with just your muscles. The more pulleys you add, the easier the work with less effort. This lesson will teach you the basics of how pulleys work. 5

6 Science Concepts What Can a Do? s help us lift objects that are too heavy to lift with our muscles alone. The pulley is a simple wheel and axle system that uses a rope or string to gain mechanical advantage that can help us lift heavy objects relatively easily. The pulley can be used to change directions. In Example 1, the input force is pulling down which in turn, moves the load up. In this example, the force needed to raise the load is equal to the effort so no mechanical advantage is achieved. However, by adding additional pulleys, the amount of force required to lift an object is reduced. Types of s Additional pulleys can be added to increase the mechancial advantage and make it easier to lift or pull heavy objects, but more rope or string is required to lift them. 1 Fixed Effort Load Single Fixed Fixed Fixed Fixed Effort Moveable Effort Moveable Load Load 2 Single Fixed/Single Moveable 3 Double Fixed/Single Moveable 6

7 Technology & Engineering Using s s are used in many different ways to help create mechanical advantage or to transfer motion from one direction to another. s can be attached to motors and can control lift and position, such as in the elevator system shown to the right. Examples Some other common uses of pulleys include large cranes, winches, block and tackles, machines, and raising a flag up and down a flagpole. Examples of common pulley systems are shown below: Elevator System Motor Winch Block and Tackle Water Well Crane Flag Pole Belt s Build a In order to understand how a pulley system works, let s build one. You will be using the components in the Rokenbok SnapStack Module or Advanced Projects Lab to build a pulley system that demonstrates mechanical advantage. 7

8 Build Plan: STEM-Maker Build: Follow the step-by-step instructions to build a pulley system. 1 Build the Base Components 4x 2x 3x 2 Build Vertical Support Beam Components 3x 3x 2x 8

9 Build Plan: 3 Attach Structural Supports Components 1x 3x 3x 1x 3x 4 Build Support Bracket Components 3x 3x 4x 4x 5x 1x 2x 9

10 Build Plan: 5 Connect Bracket to Vertical Support 6 Attach Measuring Marks Components 4x 2x 10

11 Build Plan: 7 Assemble Weights Components 2x Step 1 Cut off a piece of string that is 62cm long. Place each end of the string on top of the red connector blocks as shown. Use a single snap block to lock the string in place. 2x 2x Step 2 Connect all of the pieces together and place the string and weights over the back set of pulleys as shown. 8 Assemble Weights Components 2x 2x 1x 1x Step 1 Assemble two weights using the components listed. Cut off a piece of string that is 70cm long. Tie a knot in one end of the string. Feed the other end of the string through the pulley. Place the string between the single snap block and connector block. Snap single block into place to secure string. Step 2 Place the second set of weights on the front set of pulleys as shown. Put the tied knot in the end of the string block to secure. Note: Weight 1 should be resting on the base. The top of weight 2 should be even with the marker as shown. Adjust knot in string block if necessary. String Block Marker Weight 2 Weight 1 11

12 Math Concepts What is Mechanical Advantage? Mechanical advantage is the ratio of the force that performs the useful work of a machine to the force that is applied to the machine. What this means is that we can use mechanisms and systems to make work easier. There are many ways to achieve mechanical advantage and these concepts are used to help make difficult tasks easier. For example, a simple pulley can help us lift things that would otherwise be too heavy. To understand the concept of mechanical advantage, let s look at the two examples below. In each example, there is a load (weight) to be lifted and an effort (pull) to raise the load. Single Fixed The single fixed pulley requires an effort equal to the load in order to lift it off the ground. Because they are equal, then no mechanical advantage is achieved, but the pulley does help by changing the direction of the effort. The load goes up and the effort goes down. Single Fixed/Single Moveable The single fixed/single moveable pulley does create mechanical advantage because the load is divided between two sections of rope which requires less effort but a longer pull. MA = Load 10 Effort 10 Single Fixed = 1 MA = Single Fixed/Single Moveable Load 10 Effort 5 = 2 10cm 10cm 20cm 10cm Effort 10 Pounds Load 10 Pounds Effort 5 Pounds Load 10 Pounds Using Math to Calculate Mechanical Advantage, Effort, and Velocity Understanding simple math concepts allows an engineer to calculate technology and science concepts such as mechanical advantage, effort, and velocity. These calculations help engineers design products and structures that are strong and safe. Let s learn a little about these concepts. 12 6

13 Math Concepts Math Calculations Use the math formulas below to understand how a single fixed pulley system works. Single Fixed What is Mechanical Advantage? Mechanical Calculating advantage Effort is the ratio of the force that performs the useful work of a machine to the force The effort that is (force) applied required to the to machine. lift the load What this means 10cm is that we can use mechanisms 10cm and systems (weight) to make is equal work to easier. the load There divided are by many the ways to (velocity achieve of mechanical advantage (velocity and of these concepts number are of used lines to that help are us shortened. effort) load) do things that we would not be able to do with just our arms and muscles See formula alone. A below: simple pulley can help us lift things that we just couldn t do without them. To understand the Load concept (weight) of 10 mechanical pounds advantage, let s look at the two examples below. Effort (force) = = 10 pounds In each example, there Number is a of load Lines 1(weight) to be lifted and an effort (pull) to raise the load. Single Fixed The Using Single our Fixed example, we requires see that an effort to raise equal a 10 to the load in order to lift it off the ground. Because pound they weight are equal, 10cm high then would no mechanical require an advantage is achieved, but the pulley does help by changing force of the 10 direction pounds of and the you effort. would The have load to goes pull up and the effort goes down. the rope 10cm in order to raise it 10cm. Single Fixed/Single Moveable The Calculating Single Fixed/Single Velocity Moveable Ratio does create mechanical advantage because the load is divided The between distance two that sections the rope of travels rope which is called requires the less effort, Effort but (force) a longer pull. velocity ratio. Since the rope travels the same 10 Pounds distance in this example, then the velocity ratio Load (weight) 10 Pounds is 1:1. See formula below: V (velocity) = Distance of Effort 10cm Distance of Load 10cm = 1 Calculating Mechanical Advantage Since the load (weight) and effort (force) are equal, then there is no mechanical advantage realized with a single fixed pulley. MA = Load (weight) 10 pounds Effort (force) 10 pounds = 1 13

14 Math Concepts Math Calculations Use the math formulas below to understand how a single fixed/single moveable pulley works. Single Fixed/Single Moveable Calculating Effort The effort (force) required to lift the load (weight) is equal to the load divided by the number of lines that are shortened. See formula below: Single Fixed 5cm (velocity of load) Effort (force) = Load (weight) 10 pounds Number of Lines 2 = 5 pounds Using our example, we see that to raise a 10 pound weight 5cm high,would require a force of 5 pounds. Also, you would have to pull the rope 10cm in order to raise it 5cm. Calculating Velocity Ratio The distance that the rope travels is called the velocity ratio. The two short ropes attached to the load travel 5cm, while the effort rope must travel 10cm to lift the load 5cm. This means the velocity ratio is 2:1. See formula below: 10cm (velocity of effort) Effort (force) 5 Pounds Single Moveable V (velocity) = Distance of Effort 10 feet Distance of Load 5 feet = 2 Calculating Mechanical Advantage Since the load (weight) is lifted by two ropes, then the mechanical advantage of this pulley system is 2:1. Load (weight) 10 Pounds MA = Load (weight) 10 pounds Effort (force) 5 pounds = 2 14

15 Math Concepts Testing the System Use the pulley system to test your math calculations. 1 Testing the Fixed System Turn the pulley system around so that you can test the fixed pulley system. Notice that as you pull down on one side, the other side will move up and will stay in that position until the opposite weight is moved again. There is no mechanical advantage here. Now go to the opposite side and test the moveable pulley. Position A Position B 2 Testing the Moveable Pull the moveable pulley down from the top pulley marker to the lower pulley marker. About 10cm down. Notice how far the pulley weight is raised. (About 20cm up) 10cm Fixed Moveable 20cm Fixed Fixed Weight 10cm Fixed Moveable 20cm Fixed Release the moveable pulley and see how far the weight moves up and how far the fixed pulley weight goes down. Fixed Weight The mechanical advantage is 20cm/10cm or a 2:1 ratio. Position A Position B 15

16 Design Challenge Design Challenge: Elevator System Now that you have learned all about the pulley, it is time to apply the knowledge learned in a creative way. In this challenge, each team must design and engineer a custom elevator. Read carefully through the design brief below, then use the design and engineering process to develop the device. Design Brief: Scenario You have just inherited a bass boat from your uncle and you are excited about the many fishing trips that are to come. There is just one problem: you need to be able to lift the boat out of the water and move it into a storage garage for the winter to protect it. Design Challenge Your design challenge is to design and build an elevator system that will raise and lower your new bass boat in and out of the lake and roll it to a storage garage. Specifications The design must meet the following specifications: 1. The elevator system must raise the boat at least 18cm high from the ground. 2. Elevator must incorporate a pulley system that will raise and lower boat. 3. The elevator system must be designed to fit the boat size. 4. With each building component costing $2, the boat elevator must cost less than $ The challenge must be completed in the allotted time. 6. Write a short story about your boat lift design and be prepared to share it with your classmates. Using Resources Use the building components in the Rokenbok Education SnapStack Module or Advanced Projects Lab to complete this design challenge. 16

17 Design Process Design and Engineer Process To develop a highly functionable elevator system, we will review the process that real designers and engineers use to solve a problem. Each team will work through the steps of the design and engineering process to develop a custom elevator system. The graphic below highlights each step that will be covered throughout this activity. What is the Problem/ Opportunity? Fix and Redesign Research & Discovery Test the Design DESIGN 7 3 Process Brainstorm Ideas Build the Prototype/ Model 6 5 Develop the Plan 4 Select Solution 17

18 Design Process Using the Design Process Carefully consider each step of the design process to develop a high quality design. Step 1: Step 2: Step 3: Step 4: Step 5: Step 6: Step 7: Step 8 : What is the Problem/Opportunity? Build a boat elevator that can lift your new bass boat out of the lake and move it to a storage garage to protect it from the elements. Research and Discovery Check out availability of materials, and how to actually build a boat elevator that is safe and strong. Look online for examples. Brainstorm Ideas List all the ideas that you have found and then look at the pros and cons for each idea, considering each one carefully before making a final decision. Select a Solution Identify the best solution and move forward with your project. Develop a Plan Once you have made a decision on which solution you think is the best, then the next step is to put together a good plan for designing and building your project. Build a Prototype/Model Build a scale model of your design. Test the Design Once you build your prototype or model, you should test your design to make sure that it meets all specifications. Fix and Redesign If you have identified any problems or design issues, then go back through the design and engineering process to make any needed changes or redesigns. Once corrections have been made, then you can proceed with your project. 18

19 Design Reflection Applications of STEM Designers and engineers use science, technology and engineering, and math to solve complex problems. Let s look at some of the math and science concepts that were included in this design challenge: Science Concepts - Mechanical Advantage - Loads and Effort Technology and Engineering Concepts - Structures - Form and Function Math Concepts - Linear Measurements - Costs and Budgets Can you think of other STEM concepts that you learned from this project? Writing Your Story After you have completed your project, it is important to tell others what you have learned and experienced. One good way to share is to write your story down on paper or on the computer. Some things that you might include are: 1. What were the ideas that your team brainstormed? 2. Why did you choose the design that you built? 3. What was the most difficult part of your design? 4. What did you enjoy the most about this project? The least? 5. What did you learn about design and engineering by completing this project? Telling Your Story One fun way to complete this project is to share with your classmates about your design and what you have learned. Make sure that you speak loudly and clearly so everyone can hear and understand you. Be enthusiastic and answer any questions that might be asked. 19

20 Presentation Design Challenge Presentation When you have completed the design challenge, it should be presented to your teacher and classmates for evaluation. Your grade will be determined by how well you do on all grading critera. These include: Specifications Did you follow the rules? Design Quality Is your project strong and safe? Is it well built? Time Management Did you get your project done on time? Did you use your time wisely? Aesthetics Does your project look good? Is it balanced and proportioned? Story Did you write a good story about building your project? Presentation Did you make a good presentation? Were you interesting or unengaging? Design Challenge Presentation Assessment Your overall project will be graded on the following criteria: Grading Rubric 8-10 Points 5-7 Points 0-4 Points Specifications Meets All Specifications Meets 80% of Specifications Does Not Meet Specifications Design Quality Excellent Design Good Design Poor Design Time Management Completed on Time Completed, Not on Time Not Completed Aesthetics Balanced and Attractive Somewhat Attractive Unbalanced Unattractive Story Well Written Complete Story Fairly Written Partial Story Poorly Written Incomplete Presentation Enthusiastic Complete Unenthusiastic Partially Done Unengaging Incomplete TOTAL POINTS 20

21 Assessment What Have We Learned? 1. What are the two necessary parts for a pulley system? a. base and axle b. lever arm and fulcrum c. wheel/axle and rope or cable d. weight and effort 2. What type of pulley system is shown in this example? a. single fixed pulley b. double fixed pulley c. single fixed / double moveable pulley d. single fixed / single moveable pulley 3. Use the information below to determine the mechanical advantage of the pulley. MA = Load Effort =? MA = 10cm a. MA = 2 b. MA = 3 c. MA = 4 d. MA = 16 Effort 4 Pounds Load 8 Pounds 4. Force to overcome an object to be moved, otherwise known as load, is the definition for? a. effort b. leverage c. motion d. resistance 5. Which of the following examples would most likely use a pulley system? a. hammer b. block and tackle c. screwdriver d. file 5cm