Snow Man

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What kind of experiment is this?

Experimental procedure and explanation:

• Materials required for the experiment: large (φ 40 mm) and small (φ 30 mm) styrene foam balls, fat (φ 6 mm) and thin (φ 4.5 mm) straws, a bamboo skewer, and a styrene foam disc.
• Pierce the thin straw through the large and small balls, and then cut off the protruding parts.
• Insert the skewer onto the disc, and make a snowman.
• Question: Try to take out the balls one at a time by blowing air onto them with a straw. Where would you blow air and in which direction?
• Intermediate-level answer: Blow on top of the balls in the horizontal direction. You can take out the balls this way, but it is slightly difficult owing to friction between the balls and the skewer.
• Advanced-level answer: Blow on the top of the balls from a lower position. It is the easiest when the resultant force of lift and drag points vertically up.

[Note]	separation, Coanda effect, momentum theory
[Keywords]	Coanda effect, drag, lift, momentum theory
[Reference]	“The Wonders of Flow,” Japan Society of Mechanical Engineering, Koudansha Blue Backs, pp. 134-135
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