You may have heard that if you drop your food on the floor but pick it up within five seconds, it will not be heavily contaminated with bacteria. Let us consider the following case. You drop a circular snack with a diameter of 4 cm on the ground. The bacteria from the floor will immediately stick to it. However, according to the common rule, this should not matter. Therefore, let us assume that most of the bacteria only arrive at the food from the vicinity of the snack during those five seconds. What would their velocity have to be for their numbers to multiply tenfold on a snack in five seconds? The surface density of bacteria on the ground is homogeneous.
Jarda always blows off the fallen food so that he can eat with a peace in mind.