Is Bernoulli principle the cause of suction truck?? Hello! I’d like to know this question: When a truck walks to a high speed we see how the road tree leaves are dragged behind it. I would like to know the real cause of this problem. I think the air viscosity makes the truck drag a thin layer of air ahead. This make the quiet air moves to fill the space left by air moving. But he main reason is Bernoulli principle, isn’t it? The high speed of the air makes the pressure decrease, so the objects are dragged behind the truck. What do you think about it? Do you agree with me? Regards from Spain.