5/9/11

Tornado DamageData Analysis• The Fujita Scale is used

to determine the severity of a tornado.

• The kinds of tornadoes that can level whole buildings are in the F4 and F5 range.

Category Wind Speed (mph)

F5 261-318

F4 207-260

F3 158-206

F2 113-157

F1 73-112

F0 < 73

Tornado Damage

Angular Momentum• One of the reasons

that tornadoes have such high winds is due to the conservation of angular momentum.

Tornado Damage

Angular Momentum• The best example of

this is when a figure skater brings her arms in and increases her rate of spin.

• This video gives a clear example of this:http://youtu.be/AQLtcEAG9v0

Tornado Damage

Angular Momentum• The funnel shape of

the tornado causes the narrower part of the tornado to have a faster wind speed.

Tornado Damage

Angular Momentum• A simple model of

a tornado is a cylinder. Both tornadoes shown have the same angular momentum (L) but different radii and angular speeds.

Tornado Damage

Angular Momentum• The tornado on

the right has four times the angular speed of the tornado on the left, even though it has half the radius of the first tornado.

Tornado Damage

Centripetal Force• But how do swirling

winds create such damage to buildings?

• The swirling winds of a tornado create a strong centripetal force.

Tornado Damage

Centripetal Force• In this diagram, the

force shown is from the swirling wind. The speed (v) is the speed of the wind. The value of r is the radius of the circular swirl. And m is the mass of the wind against the building.

Tornado Damage

Centripetal Force• Calculate the

mass (m) by multiplying the air density by the volume of air.

• Think of the column of air in the tornado as a hollow cylinder.

Tornado Damage

Centripetal Force• In this diagram, the

force shown is from the swirling wind. The speed (v) is the speed of the wind. The value of r is the radius of the circular swirl. And m is the mass of the wind against the building.

Tornado Damage

Centripetal Force• Use the following data

to calculate the force on a building from an F4 tornado.

Variable Value

p 1.2 kg/m3

h 10 m

r1 8 m

r2 10 m

v 112 m/s

r 9 m

Tornado Damage

Centripetal Force• This massive force is

equivalent to nearly half a million pounds of weight!