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Gears TESLA Simple Machines 2010

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**The Big Idea of this Investigation**

A simple machine is a mechanical device that makes work easier by magnifying, modifying, transferring, or changing the direction of applied force. Simple machines are the elementary "building blocks" of which all complicated machines are made.

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**Knowledge We Will Build on From Prior Investigations**

Force is a push or pull applied to an object. Work = Distance X Force Friction is the number one enemy of simple machines. It increases the amount of force needed to do work. Wheels reduce the amount of friction between an object and the surface over which it moves. A wheel and axle can work together to magnify force and make work easier. When a large wheel is attached to a small axle the same amount of work can be completed with less force by turning the wheel.

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ENGAGING SCENARIO In previous investigations we continue to discover how simple machines can make work easier. A gear is a special type of wheel with teeth. In this investigation we need to find out how a gear can be used to make work easier by magnifying, modifying, transferring, or changing the direction of applied force. What is the problem we need to solve? What do we need to investigate? Teachers need to show the boxes to help students understand the situation. Review the clues in the engaging scenario by asking questions: how many boxes?, how are they organized?, why do we need to know how they are organized? Discuss ideas with a partner for a possible focus question. Your focus question should be connected to what the scenario wants us to do…

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**Focus Question (What is the problem?)**

How can gears be used to make work easier by magnifying, modifying, transferring, or changing the direction of applied force? Previous Knowledge Share experiences with gears How are the materials in the boxes organized? How can we find out the common property in each of the boxes? Prediction (related to the focus question) Prediction: I predict that a gear can be used to make work easier by… because____________ NOTEBOOK ENTRY 5

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**Class Predictions (related to the focus question)**

What do you think is happening inside this system? NOTEBOOK ENTRY

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New Vocabulary Gear A special type of wheel that has evenly spaced teeth around the edge. Gears can transfer force from one to another Driving Gear: A driving gear is a gear that transmits force to another gear Driven Gear: The driven gear is a gear that receives force How are the materials in the boxes organized? How can we find out the common property in each of the boxes? If you rotate the driving gear one full revolution, what happens to the driven gear? NOTEBOOK ENTRY

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**New Vocabulary Gear Ratio:**

The relationship between the number of rotations of each gear. It is written as a fraction or ratio # Rotations of the driving gear / # Rotations of the driven gear For Example 1/3 or 1:3 : How are the materials in the boxes organized? How can we find out the common property in each of the boxes? 1 Rotation Driving Gear 3 Rotations Driven Gear Why do you think the driven gear rotated three times for every rotation of the driving gear? Driven gear has 10 teeth Driving gear has 30 teeth 8

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**Collecting Data Remember… Gear Ratio is always Driving : Driven**

What is the mechanical advantage to using 3 or more gears?

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**Making Meaning Conference**

What are gears? What is the difference between a driving and driven gear? When using only 2 gears which direction does the driven gear turn if the driving gear is turned clockwise? How can you change the direction of the driven gear? What does it mean if your system has a 1:4 gear ratio? If you driving gear has 40 teeth, how many does your driven gear have? How can gears be used together to transfer force? How can gears be used together to change or magnify force?

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Claims and Evidence How can gears be used together to make work easier? I claim that… I claim this because… NOTEBOOK ENTRY

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**Reflection/Conclusion**

Revisit your original prediction… Explain how the evidence did or did not support your original prediction? My prediction was accurate because….. I wish to revise my prediction because… What did you learn… What really surprised you… What new questions do you have… What would you like to know more about… NOTEBOOK ENTRY

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Lecture 21 Using Machines Ozgur Unal

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