Elastic Potential Energy: Fall back, spring forward



Making a Better Toy: Yo-Yo

45 Minute Lesson

NJ Standards

5.2.12.E.2 – Objects undergo different kinds of motion (translational, rotational, and vibrational).

5.2.8.D.1 – Conservation of energy.

5.1.12.A.1 – Mathematical, physical, and computational tools are used to search for and explain core scientific concepts and principles.

|NJ Standard |Goal |Evidence |

|5.2.8.D.1 |Students will be able to apply rotational dynamics to understand how a simple and modern yo-yo work. |Students can reason the forces responsible for spinning a yo-yo.|

|5.2.12.E.2 | |Additionally, they can also reason to how a yo-yo can sleep at |

|5.1.12.A.1 | |the end of a fixed axle using work-energy concepts. Students |

| | |will be able to successfully build a working yo-yo out of |

| | |everyday materials. |

|5.1.12.A.1 |Students will be able to use their knowledge of rotational dynamics to propose explanations for the various |Students can use their knowledge of moment of inertia as well as|

|5.2.12.E.2 |designs of modern yo-yos. |angular acceleration to differentiate between the functions of |

| | |the various different shapes of yo-yos. |

| | | |

Resources

Student Materials:

Wooden Dowels

Scotch Tape

Cardboard , Paper

Paper, Plastic, Styrofoam Cups

Straws

Scissors

Screws and Bolts

Axle Fasteners

Yo-Yo String

Teacher Use:

Imperial Shaped Yo-Yo [RUPA Imperial Yo-Yo, Sunset Trajector NXG Yo-Yo]

Wing Shaped Yo-Yo [PhenomIZM Yo-Yo]

Yo-Yo String

Real World Applications

Moment of Inertia; Maintain your balance by increasing your moment of inertia

Angular Momentum; Angular momentum is conserved and noticeable in many real world applications, such as bicycle riding or figure skating.

Toy Design; Rotational mechanics are used to design spinning toys and further refine them and enhance their functionality .

Pre-Requisite Knowledge

Moment of inertia;

Students must understand moment of inertia, the rotational analog of inertial mass. Students should be able to differentiate between lower or greater moment of inertia in different shapes/configurations and also how the moment of inertia will affect rotational motion.

Angular Momentum;

Students must understand that angular momentum is conserved. This is crucial to understand why spinning objects persist in spinning in the direction they are spun at, particularly for a yo-yo. Students must also understand what is required for angular momentum to be changed.

Torque;

Students must understand torques which need to be exerted on a rigid body in order to rotate the system.

Work-Energy;

Students may find it useful to analyze the motion of a yo-yo with principles of gravitational potential, translational and rotational kinetic energy.

Potential Difficulties

Students may have difficulties in determining different moment of inertias and or their effects. Students may benefit by conceptual real life examples of balancing oneself on a narrow beam. Students may associate this with weight distribution and should be allowed to apply this idea to the yo-yo.

Students may have difficulties differentiating between smaller or larger moment of inertias in a yo-yo, especially where the shapes are ambiguous.

Students may have difficulties predicting the effects of different moment of inertias and relating this to the already spinning behavior of a yo-yo. Moreover, they may confuse angular momentum with the torques produced by friction that result not in the yo-yo to stop spinning, but to spin in a different direction than originally.

Lesson Description

Opening (5 minutes)

Physics can explain how the world around us work. There has also been another big application to physics, which is designing toys. The yo-yo rotates all the way back to circa 500 B.C. where Greek children played with it. Supposedly, hunters used rocks tied to 20 feet long string to hunt their prey. Finally, the word yo-yo apparently comes from a Filipino language, meaning “come-come” or “return”.

Have students draw a sketch as particular as they can of a yo-yo.

Let’s take a couple minutes to look at real yo-yo's.

Have students compare their ideas of a yo-yo to a modern yo-yo. And note what features are different.

Design Specifications (7 minutes)

A yo-yo is essentially a pair of wheels connected by an axle. How do we get a yo-yo to spin?

[Ask students how to get a yo-yo spinning on a surface – frictional forces from the surface exert a torque to rotate the yo-yo]

It’s important that we need a torque in order to get the yo-yo spinning. If we drop the yo-yo without string, what do you predict will happen?

[What do you predict will happen? – Yo-yo will spin very little if not at all, mostly straight drop (all translational kinetic energy)]

Now we’ll add string and drop the yo-yo again. What is responsible for the spin in this case?

[The wound string around the axle exerts a torque rotating the axle, rotating the yo-yo]

Have students attempt to distinguish what the purpose of each feature of the yo-yo is. Hint: What varies between the exemplary yo-yos?

[Shape, Material, String, Innards, Size, Gap for string are all things that can vary and should be noticed.]

Design Challenge: A Yo-Yo (20-30 minutes)

Now that students may have ideas about what elements are key to developing a yo-yo, have students in groups determine what features are key to designing a prototype yo-yo out of everyday materials. There are three challenges:

Challenge 1: Build a yo-yo that spins as it moves downwards and can wind itself up when tugged upon.

Challenge 2: Build a yo-yo that will spin at the end of the string.

Challenge 3: Build a yo-yo that will spin longer than the spin time from Challenge 2.

Reflection (5 minutes)

Students reflect on what they have learned. What have they learned about yo-yos and their design in light of rotational dynamics?

Time Table

|Activity |Time Duration (Clock) |Students doing |Teacher doing |

|A – Opening |5 minutes (0:05) |Listen, Think, Sketch, Observe materials |Discussion, present materials |

|B – Design Specifications |7 minutes (0:12) |Discussion |Discussion |

|C – Design Challenge: A Yo-Yo |20-30 minutes (0:32-42) |Building Yo-Yo |Observing |

|F - Reflection |3 minutes (0:45) |Reflect |Reflect |

| | | | |

| | | | |

Formative Assessment

|Ask students how to get a yo-yo spinning without string. |Roll it on a surface, frictional forces exert a torque |

|If we drop the yo-yo without string, what do you predict will happen? | Yo-yo will spin very little, mostly translational drop |

|Now we’ll add string and drop the yo-yo again. What is responsible for the spin in this case? |Torque exerted by the yo-yo inner surface on the string |

|What stops the yo-yo from spinning infinitely? |Frictional forces exerted on the axle by the string |

|If you were an engineer what is the most important factor in getting longer spin times? |Reducing friction between the axle and string |

|Between the shapes we identified (imperial and butterfly), which is |Butterfly shapes, greater moment of inertia from the outer rim weight |

|more likely to have a longer sleep time, why? | |

|Make a prediction, what will happen if the moment of inertia were not balanced, one side’s |The yo-yo tilts toward the lighter side and spins out of control. |

|weight was greater than the other? | |

| | |

| | |

|Homework |Purpose |

|Modern yo-yo's use very exotic parts or designs. On paper |Students will need to apply their knowledge of rotational |

|design a yo-yo shape to maximize spin time. What will the |physics to engineer the best yo-yo for sleeping. In |

|inner part of the halves look like / feature? Be specific. |particular they'll have to pay attention to shape of the |

| |yo-yo and a feature inside that will enable the yo-yo to |

| |start spinning and attain a high velocity to maintain |

| |angular momentum. There is no right answer since it is |

| |open-ended but students may compare and discuss the next |

| |day. |

| | |

| | |

| | |

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download