Giving water a lift

Year level: Upper primary/Lower secondary Learning outcome Students will investigate the use of pulleys (simple mechanical systems) that can reduce the effort required to haul water from a well. Students will design a simple pulley system to assist in lifting water from a well. Read Collecting water, wells and pumps in Niger Examine photos 1, 2, 4 and 5 Discuss How difficult would it be to haul water out of the well as shown in photos 1 and 2? What is a pulley? How do the pulleys shown in photos 4 and 5 make the job of collecting water easier? Activity 1 Use Pulleys: add more pulleys. Curriculum Corporation, 2008. The Le@rning Federation digital content L1200 For information about how to access this Learning Object http://www.thelearningfederation.edu.au/for_jurisdictions/australian_activities/australian_activities.html Record the information in the table Number of pulleys Crate mass (kg) Force applied by workers (N) Distance rope is pulled (m) Work done (force χ distance)                                         Write the three correct statements. It takes more force to lift things with two pulleys than one. It's easier to lift things with two pulleys than one. The more pulleys you use the less force you need to apply. With three pulleys, you need to pull more rope than with two pulleys. With three pulleys, you need to pull less rope than with two pulleys. The more pulleys that are used, the more force the workers have to apply. The amount of rope used is always the same. Discuss 1. How did the number of pulleys affect the amount of force required to lift a load? 2. How did the number of pulleys affect the distance the rope needed to be pulled? 3. How many pulleys would help the people shown in Collecting water, wells and pumps in Niger haul a 10 kilogram bucket of water from a well? 4. What effect does increasing the number of pulleys have? Activity 2: Working with pulleys Preparation (for each group) Two single pulleys Two double pulleys Two metres of cord such as that used for venetian blinds 200 gram mass (load) with hook or a loop of string 5.0 Newton spring balance Ruler Retort stand and clamp (or something similar) to hang pulleys from Note: When threading a pulley, maintain the cord’s tension by letting the mass dangle at its end. If the tension is released, the cord can come off the pulley wheel. Method 1. Make the initial set-up, as shown in the first diagram (with no pulley). Record the force applied by reading the spring balance. 2. Make the other pulley arrangements, as shown in the diagrams. Record the force applied to lift the mass 20 cm. 3. Devise some other set-ups using single and double pulleys. Measure the effort needed to raise the 200g mass (your load) 20cm. Remember to keep the mass, the length of string and the height the mass is being lifted the same for each set-up. Why? Complete a table of results. Pulley arrangement Force applied to lift load 20cm (N) No pulley   Single pulley   Two single pulleys   Two double pulleys   Two single pulleys with an extra loop of cord   Discuss Which set-up requires the least effort? Draw a detailed diagram of how you would install a pulley system (that can be operated by one person) over the wells shown in photos 4 and 5 in Collecting water, wells and pumps in Niger. Assessment task Create a report which includes: your table of results from your own pulley activity your conclusion regarding the number of pulleys compared to the effort involved in lifting the 200 gram mass your design for a pulley system for hauling water from the well. Show how your pulley system would be raised/attached to the well. Clearly show the number of pulleys you are suggesting (remember there is limited space above the well) and the rope arrangement through the pulleys. Comment on why you think your design is a good one. Extension Try The Le@rning Federation’s other activities on pulleys and loads. L1200: Pulleys: add more pulleys L4060: Lifting loads: reducing force L4061 Lifting loads: adding pulleys L4062: Lifting loads: pulling ropes L4063: Lifting loads: challenge

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