When high speed wind blows,an umbrella held upright sometimes get upturned .What is the reason being?
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first, simplest, answer is that an umbrella has a small surface ad a not-so-perfect aerodynamic shape. In order to generate enough lift to send an average person flying, it needs winds so strong that will tear it apart.
But I imagine that you would be interested in what would happen if, hypothetically, one could have an umbrella so strong that it would resist strong winds. Then the answer is that it could send a person flying, but not for an indefinite amount of time. The reason is that an umbrella generates lift only as long as it is held vertical. In this position it acts as an airplane wing, with its shape generating a lower pressure on the top side. But in order to be kept vertical, the umbrella needs to be anchored to something static relative to the moving air: the ground, through the grip of the person holding it.
Let's do a thought experiment: a person is holding an umbrella in increasing wind strength. For the purpose of this simulation, the wind is blowing perfectly parallel to the ground. As the wind increases, first enough lift is generated to offset the weight of the umbrella itself, then more and more of the person's weight. When the lift is just about equal to the weight of the person, the feet do not grip on the ground anymore and the body is dragged in the direction of the wind. The movement of the body reduces the wind as felt by the umbrella-man system (think about cycling with the wind behind your shoulders), in turn reducing the lift. Now the feet touch again the ground, and the cycle starts again. If the wind increased beyond the strength necessary to lift you, you would start moving in the direction of the wind ant increasing speed with the feet just skimming the ground.
Of course, this is a thought experiment, because in reality two extra factors would intervene: 1) one would need to keep his position upright while controlling the umbrella as a kite - which would be difficult given that an umbrella shape is not designed with aerodynamic stability in mind - and 2) the wind would need to be perfectly uniform in speed and direction - which is not.
Regarding the last point, it must be underlined that the wind does not blow always parallel to the ground. As the wind gets stronger, it becomes more and more turbulent and develops vortexes. In these vortexes the air changes direction in a upwards/downwards direction as well. Therefore if one person with a supernaturally strong umbrella was caught in one of these vortexes during a storm, he could be flown up in the air along with the flow as long as the vortex direction points upward. Vortexes, by their own nature, change direction often, and one would quickly find himself dragged down after a short fly.
In this case the umbrella would cease to generate act like a wing but rather behave like a spinnaker sail a boat, which "captures" the wind in a turbulent way. This kind of sail cannot generated lift, but generate lots of drag (remember that lift is an aerodynamic force perpendicular to the direction of the wind, while drag is aligned with it).
In some extreme cases, such as tornadoes, the wind direction can have a very strong upward component. In that case, you would be able to be lifted in the air for long stretches of time. But probably you would not even need an umbrella for that!
first, simplest, answer is that an umbrella has a small surface ad a not-so-perfect aerodynamic shape. In order to generate enough lift to send an average person flying, it needs winds so strong that will tear it apart.
But I imagine that you would be interested in what would happen if, hypothetically, one could have an umbrella so strong that it would resist strong winds. Then the answer is that it could send a person flying, but not for an indefinite amount of time. The reason is that an umbrella generates lift only as long as it is held vertical. In this position it acts as an airplane wing, with its shape generating a lower pressure on the top side. But in order to be kept vertical, the umbrella needs to be anchored to something static relative to the moving air: the ground, through the grip of the person holding it.
Let's do a thought experiment: a person is holding an umbrella in increasing wind strength. For the purpose of this simulation, the wind is blowing perfectly parallel to the ground. As the wind increases, first enough lift is generated to offset the weight of the umbrella itself, then more and more of the person's weight. When the lift is just about equal to the weight of the person, the feet do not grip on the ground anymore and the body is dragged in the direction of the wind. The movement of the body reduces the wind as felt by the umbrella-man system (think about cycling with the wind behind your shoulders), in turn reducing the lift. Now the feet touch again the ground, and the cycle starts again. If the wind increased beyond the strength necessary to lift you, you would start moving in the direction of the wind ant increasing speed with the feet just skimming the ground.
Of course, this is a thought experiment, because in reality two extra factors would intervene: 1) one would need to keep his position upright while controlling the umbrella as a kite - which would be difficult given that an umbrella shape is not designed with aerodynamic stability in mind - and 2) the wind would need to be perfectly uniform in speed and direction - which is not.
Regarding the last point, it must be underlined that the wind does not blow always parallel to the ground. As the wind gets stronger, it becomes more and more turbulent and develops vortexes. In these vortexes the air changes direction in a upwards/downwards direction as well. Therefore if one person with a supernaturally strong umbrella was caught in one of these vortexes during a storm, he could be flown up in the air along with the flow as long as the vortex direction points upward. Vortexes, by their own nature, change direction often, and one would quickly find himself dragged down after a short fly.
In this case the umbrella would cease to generate act like a wing but rather behave like a spinnaker sail a boat, which "captures" the wind in a turbulent way. This kind of sail cannot generated lift, but generate lots of drag (remember that lift is an aerodynamic force perpendicular to the direction of the wind, while drag is aligned with it).
In some extreme cases, such as tornadoes, the wind direction can have a very strong upward component. In that case, you would be able to be lifted in the air for long stretches of time. But probably you would not even need an umbrella for that!
AryanSagar:
Answer is correct
brailiest answer
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