# Is Bernoulli principle the cause of suction truck?

1. Jan 12, 2009

### hamilton333

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.

2. Jan 12, 2009

### mgb_phys

Re: Is Bernoulli principle the cause of suction truck??

There a few different aerodynamic effects at different points around the truck.
But the simplest one at the back is just that with a 2.5m wide, 3m high truck moving at 100kph - then every second the truck moves forward leaving a 20*2.5*3 = 150m^3 hole that has to be filled by air moving in from the sides.

3. Jan 12, 2009

### hamilton333

Re: Is Bernoulli principle the cause of suction truck??

Thanks for your quick answer. Then, Bernoulli principle doesn't have anything to do with this phenomenon, does it?

Regards

4. Jan 12, 2009

### mgb_phys

Re: Is Bernoulli principle the cause of suction truck??

I wouldn't have said so, Bernoulli principle describes a low pressure region caused by another flowing fluid.
Of course there are lots of different effects at different points around a moving truck so Bernoulli principle probably applies somewhere. It does explain why air is sucked out of a car when the window is open a small amount.

Last edited: Jan 12, 2009