How do we study tornadoes?      There are several ways in which scientists study the formation and lives of tornadoes. One of these is through numerical simulation. These simulations make use of the equations that govern storms and storm behavior in order to see how differences in various parameters in the equations affect the way that storms form and whether they will result in tornadoes. One of the major equations used in simulations is Newton's Second Law, which states that the force on an object is equal to the object's mass times the amount of acceleration that object is experiencing. In the atmosphere, Newton's Second Law "relates the force or acceleration of infinitesimally small collections of air molecules, which are assumed to act like a continuous blob of matter, called a parcel, to the forces acting on them. The equation of motion expresses the time rate of change of motion to all the forces acting on it" (Bluestein 65). The forces acting on the air parcel include the pressure-gradient force, which is caused by differences in pressure in both the horizontal and vertical direction and which acts from regions of high pressure to regions of low pressure, the buoyant force, the force generated by the Earth's rotation and the frictional force on the parcel of air. The combination of all of these forces provides the equation of motion for the parcel of air. This equation, along with the continuity equation, which describes how the different components of the wind velocity relate to each other, the thermodynamic equation, which describes how heat in the system is transformed into thermal energy, and equations describing the phase changes that water undergoes in the system, describes the formation and evolution of the severe thunderstorms that can breed tornadoes. The system is highly nonlinear; depending on what initial conditions are put in place for the various equations, the simulated evolution of the storm can vary greatly from run to run. It then becomes difficult to make accurate forecasts based on these models, because of the wind conditions vary just slightly from those used in the model, then weather systems can evolve in a direction completely different from the one the simulation evolved in.           Numerical simulations can be used to model what is happening inside a tornado vortex as well as modeling the formation of storms that may produce tornadoes. These simulations allow researchers to study what is happening in the vortex at different heights in the tornado and the effects of various forces on the tornado's vortex. For example, using numerical simulations it is possible to study the effects of frictional drag from the ground on the tornado's vortex. Scientists can also simulate tornadoes in the laboratory. One of the ways in which they do so is with what is known as a vortex chamber, in which fans are used to rotate the air and create a vortex similar to that which is created in a tornado. An example of this is the vortex machine at the University of Iowa; researchers there can use this machine to test what happens when tornadoes of varying strengths pass through populated areas. For example, they used it to simulate an F4 tornado that hit a church in Piedmont, Alabama in the 1990s to see why exactly the tornado caused as much damage to the church as it did, considering that the church only got hit by the outside edge of the tornado.