Although the effectiveness of hand washing in preventing the spread of pathogens and diseases has not been proven, the physics behind it have not been studied. But now a researcher Hammond Consulting Ltd. Presented in Cambridge (United Kingdom) Physics of fluids A simple model that captures the mechanics behind the process.

Imitating hand washing, Time scales This process removes particles such as viruses and bacteria. The mathematical model works on two levels, representing the hands (rough on small spatial scales) as wavy surfaces, with a thin liquid film between them.

The hands are stuck on rough surfaces Potential wells. In other words, they are at the bottom of a valley, and if they are to escape, the energy of the current must be sufficient to lead them up and out of that valley.

The strength of the fluid flowing between the hands depends on the speed of the hands during movement. Strong flow makes particles more easily removed. “Basically, flow informs you about the forces exerted by particles,” the author explains. Paul Hammond, So you can estimate how the particles move and find out if they have been deleted. “

The researcher compares the process of removing a stain from a shirt: the faster the movement, the more likely it is to come out. “If you move your hands too gently and too slowly, the forces created by the fluid are not enough to overcome the force of the particle,” says Hammond.

In any case, even if the particles are removed, the process is not fast. General recommendations of health authorities such as Centers for Disease Control and Prevention (CDC) United States, at least 20 seconds under tap.

The results of the Hammond model correspond to that time: about 20 seconds of vigorous movement is required to expel possible viruses and bacteria from the hands.

This model does not take into account the chemical or biological processes that occur when soap is used. However, knowing the systems that physically remove particles from your hands will give you hints on how to create more effective and eco-friendly soaps.

“Nowadays, we need to think a little more about what happens when washing down when chemicals leak into the environment,” Hammond recalls, acknowledging that this study does not reflect all the complexities of hand washing, but it does respond. Important questions Lays the foundation for future research.

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