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The physics of parachutes

Kedar Kulkarni

“Papa, how does a parachute work. I was watching parasailing on the beach and I noticed that the participants flying like a kite with a parachute attached to a motorboat. The chute slowly goes up in the air as the motorboat starts speeding, and then the chute opens like an umbrella and moves with the motorboat. It comes down as the boat slows down and stops. How does it rise up?” Raju had many questions.

His father, as usual, began explaining, “A parachute is like an umbrella or an inverted dome-like device which is used to reduce the speed of a falling object or a moving object by creating a drag thereby breaking the speed of the falling or the moving object. The size will depend on the load that is attached to it. Raju you most have seen that in rainy days if there is a strong breeze and you are standing with an umbrella, we need to stand facing the wind so that the wind is blowing over the umbrella. If the open-end faces the wind it becomes difficult to hold on to the umbrella and sometimes the umbrella overturns. The umbrella creates resistance to the wind and since it is made from thin rods, it gives away easily. The same concept is used in a parachute. It is made up of light material like nylon. It is used in adventure sports like skydiving where persons jump out from an aeroplane and then descend using the parachute. It can be used to airdrop food, equipments or soldiers in times of disasters. It breaks the free fall and allows the things to descend at a much slower speeds and avoid a vertical drop.”

“Papa, I have seen the air show on television, wherein the fighter planes land on the aircraft carriers and they have a parachute opening as they descend,” Raju added.

“Yes, as the landing strip on the aircraft carriers is limited in length the planes need to be controlled and stopped on that small runway. They are called drogue chutes and they provide braking by developing the drag and assisting in quick braking of the aircraft. The descending object is connected to the dome with a harness, and as the objects starts to descend the canopy opens up in a dome like shape and the air fills in. The big area of the canopy creates resistance to the fall by developing a drag and the speed of descent is drastically reduced and gives a feeling of floating in the air. Imagine that the material has to be really strong to withstand that drag and the strings with the harness must also be strong to withstand the force of the load downwards,” said his father. “There are various designs today when it comes to parachutes. The typical design is the dome-like canopy. The pilots also use parachutes in case of the engine malfunctions or in emergency situations as they eject out of the planes and land safely using parachutes.”

(Writer is a mechanical engineer and runs a hands-on science activity centre at Margao.)

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