## KamifusenBy: Shantisa Strowder

Kamifusen

#### What is Kamifusen?

• Kamifusen (紙風船)is a traditional Japanese toy.
• Kami means paper and fusen means balloon.
• The balloon is constructed from semi transparent glassine segments and it is put together similar to the way plastic segments make a beach ball.
• Kamifusen became popular in the early 1890s and it can still be found as folk toys at souvenir shops and other specialty stores in Japan and elsewhere.
Conundrum

#### Explain the “conundrum” or mystery about kamifusen.”

• A kamifusen remains inflated.
• One might think that bouncing the kamifusen would force air out of its hole and cause the balloon to deflate, but the bouncing action actually increases the kamifusen degree of inflation.
• When you repeatedly bounce the kamifusen it can make a nearly deflated kamifusen swell(or get bigger) to its fully inflated condition.
• The counterintuitive behavior of the kamifusen inflation has previously been attributed by some physicists to viscoelasticity, the property that causes a crumpled sheet of paper to slowly unfold.
Pressure Variation

#### What does “pressure variation” have to do with the way the kamifusen works?

• The kamifusen is in equilibrium with its surroundings and its pressure equals the pressure, p0, of the ambient atmosphere.
• When the balloon is struck, it does not fully return to its original shape after force is removed, but it also contracts and expands elastically, as illustrated in figure 2a ; during that process pressure deviates from the ambient value.
• As the waves propagate, pressure fluctuations force a small amount of air through the hole.
• When the balloon’s pressure at the hole is higher than atmospheric pressure, air is forced out; when it is lower, air is sucked in.
Figure 2

#### Explain what figure 2 is trying to communicate

• If that pressure variation were symmetric between its highs and lows, the amounts of air flowing in and out of the kamifusen would be equal and the balloon’s volume would not change.
• In fact, pressure difference and duration are inversely proportional to each other and satisfy (pH − p0)tH = (p0 − pL)tL.
• The amount of air moving through the balloon’s hole depends on the speed and duration of the flow.
• Bernoulli’s principle, which relates fluid motion and pressure, tells us that the speed is proportional to the square root of the pressure difference.
Material Considerations

#### What are some “material considerations?”

• The paper is not only lightweight and relatively impermeable to air, but it also has a degree of plasticity that allows it to deform easily and retain its resulting shape.
• Because of those properties, the kamifusen inflates to a volume commensurate with its air content and maintains that volume until additional air is added.
• A balloon made of plastic, rubber, or any other material that does not share the key properties of kamifusen paper would not inflate as the Japanese balloon does.
• Elastic waves, fluid motion, and the paper’s plasticity work together in the self-inflation of the kamifusen.
Rover's Landing on Mars

#### Do you think the Kamifusen could have inspired THE creation of airbags for the Rover’s landing on Mars? Explain.

I think the Kamifusen could have inspired the creation of airbags for the Rover's landing on Mars because they needed something to help protect the Rover when landing so it wouldn't break when landing. Also, when the airbag first comes out and starts bouncing on the ground it reminds me of the kamifusen because it continues to be inflated until it stops then it deflates.

#### More facts about Airbags used in space

• Airbags used in the Mars Exploration Rover mission are the same type that Mars Pathfinder used in 1997.
• Airbags must be strong enough to cushion the spacecraft if it lands on rocks or rough terrain and allow it to bounce across Mars' surface at freeway speeds after landing.
• To add to the complexity, the airbags must be inflated seconds before touchdown and deflated once safely on the ground.
• Each rover uses four airbags with six lobes each, which are all connected. Also, connection is important, since it helps abate some of the landing forces by keeping the bag system flexible and responsive to ground pressure.