Many people associate weapons with ninjas, but surprisingly many of the weapons were not used to harm others, they were used purely as diversion—a tool to fool an enemy into diverting his/her attention away from the true attack. Modern magicians are highly skilled at this task and ninjas of the past were often just as clever and skilled.

One of the most famous tools of trickery is the shuriken or japa-nese throwing star. Throwing stars come in many different styles and had anywhere from two to 30 points. These stars were often thrown into walls before enemies arrived, so that a person would immediately look at the star. The ninja could attack from the opposite side of the room or sneak out the door while the shuriken was being inspected. They were only sometimes thrown to damage an assailant.

The physics behind a throwing star are easy to understand. For example, if a Frisbee is thrown across a room, it rotates as it moves forward. There are two motions, transitional and rotational. The shape of the thing thrown affects how it moves through the air.

Some facts: • In translational motion, the object in motion stays in motion. • In rotational motion, a spinning object continues to spin. • Translational motion is dependent on the applied force and the mass of the object. • Rotational motion is dependent on the applied force and where it is applied to the mass and the distribution of mass. It is the where that changes the motion! Throwing a shuriken by twisting the wrist and tossing it by one of its point allows the star to spin as it moves. It is easier to spin something if it is thrown at a point farthest away from its axis (center).

Take a paper plate and hold it as if it were a shotput or a baseball. Throw the paper plate overhand and watch it fall to the floor a few steps away. Ask students what happened. Now throw the paper plate as if it were a frisbee. Ask students what changed. Discuss the concept of rotational spin.

Should students finish early have the design a new shuriken or have them try to skillfully (and carefully) throw a shuriken around a corner. 16

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SCHEDULE 1. Introductions and review of class objectives. 2. Have students form clans. 3. Presentation of background material. 4. Perform the Demonstration. 5. Student teams create a paper shuriken. 6. Students modify their shuriken for optimal performance. 7. Students put away materials and clean up. 8. Students have a shuriken throwing competition.

Background

Demonstration

master Challenge

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Paper PencilScissors

3. Take the bottom left-hand corner and fold it until the upper left-hand corner is cut in half.

4. This is how you make a square.

1. Make your own shuriken using one piece of paper.

2. Begin with a piece of notebook paper, with the longest side at the top.

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5. Cut the non-folded edge off.

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7. Fold each of the two pieces in half horizontally again.

6. Fold the square in half and then cut it in the middle to make two equal pieces.

8. Flatten each piece as flat as possible. The openings should be facing each other.

9. Fold the corners as shown along the lines shown. Be sure to fold both sides of each at once.

10. Make the folds as even with the top as possible. Make 90 degree folds whenever possible.

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11. Take the top paper and turn it over so the folds are facing the table. Leave the bottom one alone for now. Do the next few steps with the paper this direc-tion.

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13. Make a fold where the dot-ted line is shown. You will be fold the paper under.

12. Fold the top so it folds under and makes a 90 degree angle.

14. Fold the paper under and up. Make it a 90 degree fold so it matches the picture.

15. Once you have one com-plete. You will need to make the second paper exactly the same as the first. Follow steps 11-14 to create a sec-ond.

16. Set the second paper piece on the other in the design shown. The bottom paper is colored gray for help with making the star only. The smooth center should be fac-ing upward.

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17. If you have trouble you may color your bottom paper.

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19. Choose one of the cor-ners and fold it into the center. Following clockwise, fold in the next point. Be sure to fold it on the line you created in the last step. This fold should go on top of the first.

18. Make a fold line on each of the ends of the papers as shown.

20. Continue folding the next two points over the preceding point. The last point will rest on top of the center.

21. Take the center and tuck it under the edge of the previ-ous point.

22. Continue counterclock-wise tucking in the point into the previous fold. It should hold together on its own, and the center folds will look like an X if the star was made correctly.

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23. You should now have a fin-ished shuriken!

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25. Attempt to throw your shuriken safely at a wall or target. Try throwing it as if you were throwing it overhand but hold it by one point. What does it do, describe the motion?

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24. Rules of the ninja in training. • Do not throw the shuriken at other training ninjas! • Do not throw the shuriken at your sensei. • Always aim low, so you will not risk hitting someone’s face accidentally.

26. Now throw it as if it were a Frisbee by holding one of the points. How does it fly? Describe the motion.

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27. Throw the shuriken once again like a Frisbee, only this time hold it in the center instead by one of the points. Does it fly well? Does it rotate as much?

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28. Modify your shuriken so it flies better. Use materials you have access to in order to modify it. Test it until it flies accurately. Remember, a shuriken is a great diversion! Place one to divert attention.

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