Category: Fluids

Figure 14-18 represents a tube through which an ideal fluid is flowing at a steady rate. In a time interval Δt, suppose that a volume of fluid ΔV, colored purple in Fig. 14-18, enters the tube at the left (or input) end and an identical volume, colored green in Fig. 14-18, emerges at the right (or output) end.…

You may have noticed that you can increase the speed of the water emerging from a garden hose by partially closing the hose opening with your thumb. Apparently the speed v of the water depends on the cross-sectional area A through which the water flows. Here we wish to derive an expression that relates v and A for the steady flow of an…

The motion of real fluids is very complicated and not yet fully understood. Instead, we shall discuss the motion of an ideal fluid, which is simpler to handle mathematically and yet provides useful results. Here are four assumptions that we make about our ideal fluid; they all are concerned with flow: 1. Steady flow In steady (or laminar) flow, the velocity of the moving fluid…

Figure 14-9 shows a student in a swimming pool, manipulating a very thin plastic sack (of negligible mass) that is filled with water. She finds that the sack and its contained water are in static equilibrium, tending neither to rise nor to sink. The downward gravitational force  on the contained water must be balanced by a net…

When you squeeze one end of a tube to get toothpaste out the other end, you are watching Pascal’s principle in action. This principle is also the basis for the Heimlich maneuver, in which a sharp pressure increase properly applied to the abdomen is transmitted to the throat, forcefully ejecting food lodged there. The principle was first…

The Mercury Barometer Figure 14-5a shows a very basic mercury barometer, a device used to measure the pressure of the atmosphere. The long glass tube is filled with mercury and inverted with its open end in a dish of mercury, as the figure shows. The space above the mercury column contains only mercury vapor, whose pressure is…

Figure 14-2a shows a tank of water—or other liquid—open to the atmosphere. As every diver knows, the pressure increases with depth below the air–water interface. The diver’s depth gauge, in fact, is a pressure sensor much like that of Fig. 14-1b. As every mountaineer knows, the pressure decreases with altitude as one ascends into the atmosphere. The pressures encountered by the…

When we discuss rigid bodies, we are concerned with particular lumps of matter, such as wooden blocks, baseballs, or metal rods. Physical quantities that we find useful, and in whose terms we express Newton’s laws, are mass and force. We might speak, for example, of a 3.6 kg block acted on by a 25 N force. With fluids, we…

A fluid, in contrast to a solid, is a substance that can flow. Fluids conform to the boundaries of any container in which we put them. They do so because a fluid cannot sustain a force that is tangential to its surface. (In the more formal language of Section 12-7, a fluid is a substance that flows…

Many types of race cars depend on negative lift (also called downforce) to push them down against the track surface so they can take turns quickly without sliding out into the track wall. Part of the negative lift on a car is due to one or more wings on the car, and in the wind…