Use the Stepped Spool with MacGyver Windmill
As of 2016, new MacGyver Windmill Class Packs are sold with our Stepped Spool. But if you have an older MacGyver kit, or even a KidWind Wind Experiment kit, you can purchase our Stepped Spools separately and replace the regular weightlifting spool that came in your kit. The Stepped Spool's unique three-tiered design allows you to experiment with the shaft diameter. This variable is important in affecting how quickly the string lifts weight, and also on how much weight you can lift. Try it for yourself! During this activity, your goal is to measure the difference in time (seconds) that it takes for your MacGyver Windmill to lift weight on each of the three levels of the Stepped Spool.
- Preparation time: 5-10 minutes
- Learning time: 10-30 minutes
- Estimated materials cost: $5
- Grade range: 3rd-12th grade
- Exchange the regular spool on your MacGyver Windmill for the Stepped Spool.
Attach the string to the first level of the Stepped Spool. Put a few weights in the cup. Place the windmill in front your your fan. Measure the time it takes (seconds) for your cup to wind fully.
Repeat on the second level of the Stepped Spool, maintaining all variables constant (the same MacGyver Windmill design, the same number of washers, the same distance from the fan, the same fan speed, and the same string length).
Repeat once more for the third level of the Stepped Spool, maintaining all variables constant.
- So, how do the different shaft diameters affect how quickly the weight is lifted?
Now that you know which shaft diameter lifts weight the quickest, you can also calculate for which shaft diameter allows your windmill to do the most mechanical power. First, let's calculate the work your windmill is doing.
- You will use the following equation to calculate for work: Work (J) = Mass of washers (kg) x Acceleration of gravity (N/kg) x Distance (m)
- Measure the total mass of your washer(s). If you're using our kit, a single washer is 15 g (0.015 kg).
- The acceleration of gravity on earth is constant, 9.8 N/kg.
- Measure the length of the string you used from the base of the tape to the tie for the cup (the part of the string that winds up the spool), which is the distance your weight traveled.
And finally, let's find out which shaft diameter has the most mecahnical power potential (meaning it can lift the most weight).
- Calculate for mechanical power for each of the three shaft diameters using this equation: Mechanical Power = Work (J) / Time (s)
- Plug in the values from your time trials, and the value for your windmill's work from the first equation.
- Which shaft diameter can lift the most weight based on your calculation? If you test it out using your turbine, does you calculation make sense?