Imbalance and Unequal Gears – 3 of 4
Project 3 of 4
The following lesson is part of a series that should be explored in a sequential manner. Students will need the full exploration each concept in order to move from one phase of Levers, Arms and Fulcrum Points to the next. It is more than just play at this level. The purpose of these exercises is to take the concept of play into the field of science. It may not be easy, but it’s certainly will be fun!
This plan introduces skills of collaboration, problem solving, new understanding of mechanical advantage .
Age Group: 3-5
Time: 40 minutes
Main Goal: Collaboration, problem solving, new understanding of mechanical advantage.
Guiding and supporting play
- Observe, observe, observe!
- Allow children to explore their own Rigamajig play ideas. There is no set formula for “right” or “wrong” outcomes.
- Children may produce a variety of Rigamajig ideas to meet the basic objectives of the lesson plan. No two creations or play sessions are alike. Be comfortable with letting children’s play evolve.
- There are no mistakes, let them explore and problem solve.
- Resist the urge to “fix” things for children and to show or tell children how to do things. Observe, and pay attention to children’s ideas and actions. Support play in ways that focus children on their own ideas. Ask about what students are planning to do, what they are making, and what they can change to make their Rigamajig work better?
- Discover insights into children’s creative thinking, and foster creativity!
- Rigamajig Basic Builder Kit
- Simple Machines Add-on Kit
Ask students to build a fulcrum point and balance a long plank as they have previously done in the last project plan. Then ask students to add a weight to one side of the balance beam. Have students then move the plank along the fulcrum point until it is balanced. Allow time for students to play and experiment with this and to test different weights.
- HINT: Students will find that the shorter one side of the beam is, the more weight it can hold. Use this discovery to explain the principle of lever arms:
- A lever arm is measured from the end of the arm to the fulcrum point
- Short lever arms can be used to apply more force or hold more weight
- The trade-off is force for distance. The short arm can lift heavier things, but it can’t lift them as far as the long arm
- Give examples of levers like scissors or wheelbarrows! Can they find the lever arms and fulcrum points? Note that on a wheelbarrow the fulcrum point is not in the middle, but on the end! Can they figure out what part of the wheelbarrow is the fulcrum point? Where are the lever arms?
- Have students experiment with this and have then make a wheelbarrow.
- HINT: A wheel spinning around an axle on the end of a long plank works well for this, but see what other solutions they come up with!
- It may be worth spending a whole session exploring and playing with lever arms before expanding these concepts to gears of different sizes.
- After ample exploration with levers, explain to students that they will now experiment with different size gears. Have students find two gears of different sizes that mesh together. Then have them draw the lever arms on the gears by drawing a straight line from the center of a gear to the middle of a gear tooth.
- This allows students to visualize the lever arm as they keep track of the number of rotations the gears make.
- HINT: Notice the length of the lever arm on the small gear compared to the lever arm on the big gear. As students begin to see the the two different sized gears rotate, they will see that the smaller gear is rotating at a faster speed. This is a good time to interrupt exploration to talk about what is happening.
- HINT: Ask students what they notice about the rate at which the smaller gear is rotating compared to the rate of the larger gear. Students will discover that the small gear is rotating faster. This is because it is being driven by the long lever arm of the large gear. Explain that this is similar to the lever arms on the balance beam. The large gear can move a greater distance at the end of its long lever arm. This greater distance applies more speed to the small gear.
- The number of rotations will be counted later in phase 3 as gear ratios are explained.
- By applying this same model but then switching the perspective, students will discover that if the small gear is driving the larger gear it will apply more force.
- HINT: This is a result of the stronger short lever arm on the small gear pushing the teeth on the large gear. It can drive larger gears with more force, but they will turn more slowly.
- Now that students have had this experience of having a larger gear drive a smaller gear and vice versa, they can compare this to how the short lever arm on the balance beam was able to hold more weight. This is mechanical advantage in action.
While play is underway
Observe with an interested and supportive attitude and, as needed, encourage problem solving thinking, creativity, collaboration, discussion, and questions.
Real World Example: Bicycles
While speed is easy to visualize, the concept of force may be harder to grasp. A great practical example is a bicycle. Have any students noticed that it can be hard to pedal up a hill on a bicycle, but shifting to a lower gear makes it easier? Or that using a low gear on flat ground is slower and does not get you as far as using a high gear?
That is because bicycles have gears too! They are actually called sprockets because they are a little bit different. Notice that the sprockets on a bicycle move in the same direction as the pedal turns the back wheel. That is because they are connected with a chain in the same way pulleys are connected with belts. The sprockets work like pulleys but with the positive drive of gear teeth that do not slip.
Lower gears on a bicycle have a smaller sprocket connected to the pedal which is linked to a larger sprocket on the wheel. The opposite is true in a higher gear. There may even be a setting where the pedal moves at the same speed as the wheel! If possible bring a bicycle into the classroom to demonstrate. Set it upside down on top of a table and change gears while turning the pedal. Watch the rate of the pedal and compare to a reflector on the spokes of the back wheel. If there is no reflector, use a piece of tape or a sticker on the side of the back tire
Post some of the following words on a White Board, SmartBoard, sheet of chart paper or have the students make their vocabulary lists or posters of the key words. Encourage children’s use of these words as they design and build. Encourage children to label the physical components of their creations.
- Lever Arm
- Solve Problem
What to look for
- Watch for children’s collaborations in their thinking and construction. Offer encouraging words about working together to build something.
- Pay particular attention to how children go about their construction process. Do they seem to have a specific goal? Or, do they seem more focused on learning about the properties of the materials and different things they can do with them?
- Pay attention to the language. What do their words reveal about their knowledge of objects, physical processes, design, and/or social collaboration?
- When children indicate they accomplished something, give them a chance to demonstrate their construction and how it works, and share with other children.
What if the children “stall”?
- Sit with the group and ask them to discuss their ideas for what to build. Can they agree on something?
- Reinforce that any kind of construction is OK, it’s whatever they want to do!
- Pick up a few pieces and put them together for children to see. Don’t be afraid to model taking a risk, exploring, or changing an initial idea.
Wrapping up & reflecting
- What are you (were you) most curious about?
- What made for good collaboration?
- Tell us about a problem you encountered and your group’s solution.
- Create drawings and descriptions or photographs and descriptions of work, including step by step as preferred
- Share and present work, include discuss about how and why construction decisions were made
Education standards addressed
- 3-5 – ETS1- Engineering Design NGSS
- Meets Common Core Math Standards 6th and 7th grade Ratio and Proportional Relationships
- 21st Century Skills
Download project plan
With the help our Captain of Play and Learing Ngina Johnson, we’ve put together a few project plans to get you started. If you have any projects you’d like to share with the world, please email us at firstname.lastname@example.org
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