> *All fans suck air in from thrugh the back and push it out the front. It has enough power to blow stuff around, why can't it suck stuff in?



It turns out that if you have one of the large, square prism models with non-porous lateral sides, it will "suck" in a piece of paper or such from the backside if you hold it within, say, 6 inches (15 cm).

A round fan with porous sides or no apparent sides at all (quasi-extruded elliptical circle model) will generally not "suck in" a piece of paper as well.

These differences are most likely directly related to the power of the fan motor (higher in square-type models), the direction from which the air is intended to enter the fan, and the shape of the blades (which causes air to enter from different angles). A square-type model is generally intended to take in air from one direction only, such as when placed in front of a window or screen door. This assists in a strong attraction from the rear of the fan and a greater distance from which the fan draws a piece of paper or such inward to the fan. A circular-type model, however, is usually intended only to create air flow within a room and not to move air from outside a room to the inside. For this reason the range of angles from which the air is drawn in is greater and hence the amount of air entering the fan from any given spot is smaller than for a square type fan. This means that there is less attraction on pieces of paper with the same surface area and mass to a circular fan than to a square fan.

The apparent amount of air entering the fan from the rear versus the amount exiting from the front appears to be much less because the angle of spread of the air coming from the front of the fan is much narrower than that coming from the back of the fan.

Augment to these facts that square fans often have the higher motor speed and larger blade size, and you have the reason why with the more common circular fan model you view less "sucking" in from the back of the fan.

EXTIRPATOR