Rotating Thunmderstorms and Angular Momentum?

Rotating Thunderstorms and Tornadoes?

by Steve Horstmeyer, Meteorologist, Cincinnati, Ohio, USA

MOMENTUM is the total amount of kinetic energy (that's the energy of motion). A MiniCooper traveling at 50 mph (80 km per hr.) has much less total kinetic energy than a 18-Wheeler also traveling 50 mph.
Looking at it another way a Major League Baseball pitched at 90 mph (145 km per hr.) has twice the kinetic energy than if thrown at 45mph (72 km per hr.)

There is nothing special about an object traveling in a curve, instead of a nearly straight line. Momentum is now called ANGULAR MOMENTUM. It is still the total kinetic energy, but now the path of movement is a curve, and mathematically it is expressed a bit differently, however it is the same concept - TOTAL KINETIC ENERGY.

THERE IS A COMPLICATION WITH CURVED FLOW if the object gets closer to the axis of rotation. Think of ice skaters who pull their arms in towards the body and spin faster, or a high diver who curls up on the way down to spin faster to do more somersaults. By pulling mass towards the center of rotation, the rate of spin increases because angular momentum is conserved. Moving mass away from the axis decreases the rate of spin.

Think of it this way, if the mass gets closer to the axis it is not traveling as far with each rotation and unless some force puts on the brakes (investigate a concept called inertia) it must travel faster.THAT IS JUST A BASIC APPLICATION OF NEWTON'S FIRST LAW OF MOTION

So you see it is not really special, an object moving in a curved path or straight line will not slow unless a force (like friction or the forces of air pushing around it) acts on it.

The object can be a mass of air drawn from many miles in all directions into a supercell thunderstorm, bacause of something called the coriolis (core-ee-oh-liss) effect the air will travel in a curved path as it flows into the thunderstorm and NOW YOU KNOW it's angular momentum will be conserved. This is a way the spin is increased in a thunderstorm and can lead to a tornado. (Note: some of the momentum is transferred to the ground and objects like houses and trees that the air spiraling into the thunderstorm encounters on its journey to the updraft core.)


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