Table of Contents. Career Overview... 4

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Clinton Allison
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1 Table of Contents Career Overview Basic Lesson Plans Activity 1 Measuring... 6 Activity 2 Accuracy and Precision Activity 3 Measurement Devices Activity 4 Exploring Density Challenge 1 Rocky Measurements Activity 5 Simple Machines: Levers Activity Pulley Extension Activities (optional)...52 Challenge 2 Rube Goldberg Machine Standards Addressed...63 Puzzles...73 Glossary Assessment Links of Interest

2 Teacher Procedure Objective Students experience the mechanical advantage provided by pulleys or a pulley system. Background Two common ways to use a pulley to lift a load is with a fixed pulley or movable pulley. Fixed pulley the frame is attached to a ceiling or beam and the load is attached to the cord. This allows the load to be moved upwards by pulling downwards from the ground (like the pulley on a flagpole). Simple machines offer mechanical advantage, which makes a task easier or require less force. However, it may require more time or room to work. For example, applying a smaller force over a longer distance to achieve the same effect as applying a large force over a small distance. The ratio of the output force exerted by a machine to the input force applied to it is the mechanical advantage of the machine. Pulley Rope Pulleys are an excellent example of the mechanical advantage offered by simple machines. A simple pulley consists of a wheel with a groove around the edge, set in a frame. Pulleys are used to change the direction of a force. The force is applied to an object by the tension in a cord that lies in the pulley s groove. The frame is used to attach the pulley to a fixed object (like a ceiling) or to a load. Engineers are experts at exploiting the advantages of simple machines in all sorts of real-world applications that benefit society. They incorporate the mechanical advantage of pulleys into their design of many modern-day structures, machines, products and tools, such as cranes, elevators, flagpoles, zip lines, motors, bicycle rings/chains, clothes lines, water well bucket/ rope, rock climbing devices, window blinds, and sail/fishing boats. Using multiple pulleys in conjunction with motors and electronics, engineers create complex modern devices that perform much work for very little power. Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder 47 Force 10 kg Movable pulley the cord is fixed to a ceiling or beam and the load is attached to the frame. The load is raised by pulling up from a higher level. Attached MA = 2 Pulley Load-supporting rope 10 kg Object Load-supporting rope Force 5 kg 10 kg Object

3 Teacher Procedure Engineers often combine fixed and movable pulleys into systems to gain a mechanical advantage or greatly reduce the amount of force required to move an object. You will notice in the pictures below that the second system requires only half the force to lift the same amount of material as the first. The mechanical advantage, MA, determined by counting the number of load-supporting ropes, is twice as high. Procedure 1Following the, have students build fixed, movable, and combined pulley systems to learn about mechanical advantage. Attached MA = 2 Movable Pulley Load-supporting rope Load-supporting rope Fixed Pulley Redirecting-only rope Object 10 kg Force 5 kg Attached MA = 4 Force 2.5 kg Fixed Pulleys Loadsupporting ropes Movable Pulleys 10 kg 48

4 Vocabulary effort fixed pulley force load mechanical advantage movable pulley Materials Forces & Simple Machines Kit Hooked 100-, 200-, 300-gram weights Spring scale Pulley Cord Pulley Data Sheet Procedure The Fixed Pulley 1Hang the pulley from the upper hooked collar, thread the cord through the top of the frame, and lay it into the pulley groove. 2Attach a weight hanger to the left end of the cord and the upper hook of the spring scale to the right end. Add weights to the weight hanger until the weight of the spring scale is balanced and the weight hanger does not move up or down when released. 3Now attach the spring scale s lower hook to the lower hook collar and add a 100-gram weight to the weight hanger. 1Screw the support rod into the tripod base and attach one of the hooked collars to the upright support rod about three centimeters above the base with the open end of the hook pointing downward. 2Attach the second hooked collar to the support rod near the top with the hook pointing upward. 3Tie a loop on each end of the length of pulley cord. 4Read the value shown on the spring scale in grams and record it on the Pulley Data Sheet. 5Exchange the 100-gram weight for a 200-gram weight and record the new spring scale value. 6Now unhook the lower spring scale hook from the hook collar and, holding the lower spring scale hook, move the spring scale outward to several different angles. Note what happens to the reading of the spring scale when you do this. 49

5 The Movable Pulley 1Remove the spring scale and weight hanger and unhook the pulley frame from the upper hook collar. 2Attach one end of the cord to the upper hook collar, thread the cord through the lower end of the pulley frame, lay the cord into the pulley groove, and attach the free end to the spring scale s lower hook. (You may hang the spring scale s upper hook onto the upper hook collar while setting up.) 3Add 100 grams of weight to the weight hanger and hook it onto the lower end of the pulley frame. 4Hold the spring scale by the upper hook so that the pulley cords are close to vertical and record the spring scale value in grams. 5Repeat this measurement with 200 grams and 300 grams on the weight hanger. 50

6 Fixed Pulley Pulley Data Sheet Load (g) 100 Spring Scale Reading (g) What did you notice when you moved the spring scale to different angles? 2. How does the spring scale reading (the effort) compare to the load? 3. Does the fixed pulley offer a mechanical advantage? 4. Does the angle of effort make a difference? Movable Pulley Load (g) Spring Scale Reading (g) How does the spring scale reading (the effort) compare to the load? 2. Does the movable pulley offer a mechanical advantage? 3. If you wanted to lift a large load, would it be easier with a fixed pulley or a movable one? 51

7 Pulley Extension Activities Vocabulary tandem pulley Materials All materials from the Simple Machines: Pulleys activity Extra pulleys Tandem pulleys Pulleys Extension Data Sheet Procedure Single-Pulley System 4Hang the weight hanger from the lower hook of the movable pulley and hold the spring scale in your hand near the bottom of the vertical support rod. Now place the cord into the grooves of the pulleys. 5Add weights to the hanger until the weight of the spring scale is a little more than balanced (the spring scale tends to move upward). 6Add a 100-gram weight to the hanger and record the value of the spring scale reading (the effort) in grams on the data sheet. 1Hang one of the single pulleys onto the support rod. (You may have to open the eye slightly to make it fit.) 7Add weights and record the spring scale readings for loads of 200 and 300 grams. 2Attach one of the pulley cord loops of the shorter cord to the upper hook of the spring scale and temporarily hang the spring scale from the support rod s thumbscrew. 8Note that there are two strings supporting the load and the movable pulley. Record this. Tandem (Four and Six) Pulleys 3Thread the other end of the cord through the top of the pulley frame and then through one end of the second pulley frame. Then slide the loop at the free end of the cord over the support rod. 1Hang one of the tandem pulleys onto the support rod with the largest pulley at the top. 2Attach the loop of the longer cord to the lower eye of the tandem pulley. 55

8 Pulley Extension Activities 3Hold the second tandem pulley below the first with the smallest pulleys facing each other. 4Thread the cord carefully through two sets of pulleys. Make sure the cord is securely in all the grooves. 5Hang the weight hanger and add 100 grams. 6Keeping hold of the free end of the cord, attach the spring scale s upper hook to the hook collar and tie the free end of the cord to the spring scale s lower hook. 7Add weights to balance the spring scale and zero it as before. 8One at a time, switch out the 100-gram weight for the 200-gram, 300-gram, and 400-gram weights. Record the values on your data sheet. 9Add two more pulleys and record the differences. 56

Activity 3: Pulleys. Background

Activity 3: Pulleys. Background Activity 3: Pulleys Background Pulleys are simple machines that consist of a grooved wheel that turns around a fixed point, similar to the fulcrum of a lever. A rope, cord, or chain runs along the groove