# Why does a vortex have so much suction power?

A vortex that's on the ground(tornado) can rip tiles off a roof of a house and basically sucks in the roof tiles. On an aircraft that develops vortex lift the vortex sucks in air molecules and reduces the pressure on the wing. When there is a dust devil is sucks in a lot of dust and throws it. So why does a vortex have so much suction power.

• Low pressure in a tornado, high pressure around it. – CoilKid Oct 8 '15 at 2:45

If we consider the incompressible, 1-dimensional Euler equations (basically $F=ma$ but for a fluid without viscosity), the equation looks like:

$$\frac{\partial u}{\partial t} + u\frac{\partial u}{\partial x} = -\frac{1}{\rho}\frac{\partial p}{\partial x}$$

The left-hand side is the acceleration of a small lump of fluid and the right hand side is the force divided by the mass. Since we said this is inviscid, there is only the pressure gradient.

The negative sign in front of the pressure gradient means the acceleration vector is in the opposite direction of the pressure gradient vector. Gradient vectors go from low to high, and so the acceleration is in the direction of high pressure to low pressure.

The core of a vortex is, in general, a pressure minimum (although viscosity changes this slightly, not enough to talk about here). Therefore, there is a force from the outside of the vortex to the inside of the vortex; this is the suction force you are talking about. It is based entirely on how low the pressure can get inside the vortex relative to outside.

To get more suction, you need to make the pressure lower.

The low pressure inside the tornado against the high pressure outside the tornado creates a partial vacuum.