(a) A Bunsen burner uses an adjustable gas nozzle, entraining air for proper combustion. Examples of entrainment devices that use increased fluid speed to create low pressures, which then entrain one fluid into another. Some other devices that use the concept of entrainment are shown in Figure 2. Entrainment devices have been in use since ancient times, particularly as pumps to raise water small heights, as in draining swamps, fields, or other low-lying areas. With a higher pressure on the outside, the high-velocity fluid forces other fluids into the stream. People have long put the Bernoulli principle to work by using reduced pressure in high-velocity fluids to move things about. There are a number of devices and situations in which fluid flows at a constant height and, thus, can be analyzed with Bernoulli’s principle.

The pressure in the nozzle must be atmospheric since it emerges into the atmosphere without other changes in conditions. This absolute pressure in the hose is greater than in the nozzle, as expected since vv is greater in the nozzle. Greater pressure on the outside pushes the car and truck together. Air passing between the vehicles flows in a narrower channel and must increase its speed ( v 2 is greater than v 1), causing the pressure between them to drop ( P iis less than P o).

An overhead view of a car passing a truck on a highway. (See Figure 1.) This effect was observed as far back as the mid-1800s, when it was found that trains passing in opposite directions tipped precariously toward one another. The reason is the same-the high velocity of the air between the car and the truck creates a region of lower pressure, and the vehicles are pushed together by greater pressure on the outside. You may also have noticed that when passing a truck on the highway, your car tends to veer toward it. The pressure difference results in a net force inward pushing the curtain in. The high-velocity stream of water and air creates a region of lower pressure inside the shower, and standard atmospheric pressure on the other side. Shower curtains have a disagreeable habit of bulging into the shower stall when the shower is on. There are a number of common examples of pressure dropping in rapidly-moving fluids. As a result, the pressure will drop in a rapidly-moving fluid, whether or not the fluid is confined to a tube. The net work done increases the fluid’s kinetic energy. This pressure difference results in a net force on the fluid: recall that pressure times area equals force.

There is a pressure difference when the channel narrows.

Bernoulli principle gases