CH13VOCABULARY

Chapter 13 Vocabulary

** Pressure ** —the result of a force distributed over an area. A ** fluid ** is a substance that assumes the shape of its container.
 * To calculate pressure, divide the force by the area over which the force acts.
 * In the formula, force should be in newtons (N) and area should be in square meters (m2).
 * The resulting unit, newtons per square meter (N/m2), is the SI unit of pressure, also known as a ** pascal ** (Pa).
 * The pascal is named for French scientist Blaise Pascal (1623–1662). Pressures are often stated in units of kilopascals (kPa). Note that 1 kPa is 1000 Pa.
 * Both liquids and gases are fluids. Water, oil, gasoline, air, and helium are fluids.
 * The particles that make up liquids and gases are shown in Figure 2.

Water pressure increases as depth increases.
 * The pressure in a fluid at any given depth is constant, and it is exerted equally in all directions.

Air pressure decreases   as the altitude increases.

A ** hydraulic system ** is a device that uses pressurized fluid acting on pistons of different sizes to change a force.

In a hydraulic lift system, an increased output force is produced because a constant fluid pressure is exerted on the larger area of the output piston.

According to Bernoulli's principle, as the speed of a fluid increases, the pressure within the fluid decreases. [|See more here!] or [|Another one HERE!]
 * As the air blows across the top of the paper, the pressure exerted by the air decreases.
 * Because the air below the paper is nearly motionless, it exerts a greater pressure.
 * The difference in pressure forces the paper upward.

The ability of birds and airplanes to fly is largely explained by Bernoulli's principle. As shown in Figure 8, the air traveling over the top of an airplane wing moves faster than the air passing underneath.
 * This creates a low-pressure area above the wing.
 * The pressure difference between the top and the bottom of the wing creates an upward force known as ** lift **.
 * The lift created in this way is a large part of what keeps the airplane aloft.

You are easily able to lift a friend submerged in water because of buoyancy. **Figure 10** The forces from pressure acting on the bottom of this golf ball are greater than those acting on the top. This produces a net force—called the buoyant force—that acts upward on the ball. ||
 * **<span style="color: rgb(244, 42, 42)"> Buoyancy ** is the ability of a fluid to exert an upward force on an object placed in it.
 * In fact, every object in a fluid experiences buoyancy.
 * When an object is submerged in water, the water exerts an upward force on the object, making it easier to lift.
 * This upward force, which acts in the opposite direction of gravity, is called a <span style="color: rgb(246, 40, 40)">** buoyant force **.
 * [[image:http://www.pearsonsuccessnet.com/ebook/products/0-13-069977-2/hsp00493c04.jpg]] ||  ||
 * [[image:http://www.pearsonsuccessnet.com/ebook/products/0-13-069977-2/hsp00493c04.jpg]] ||  ||

<span style="color: rgb(240, 45, 45)">Archimedes, an ancient Greek mathematician who died in 212 b.c. , is credited with an important discovery that bears his name.
 * According to <span style="color: rgb(233, 22, 22)">** Archimedes' principle **, the buoyant force on an object is equal to the weight of the fluid displaced by the object.

=Density and Buoyancy= If an object is less dense than the fluid it is in, it will float. If the object is more dense than the fluid it is in, it will sink. When the buoyant force is equal to the weight, an object floats or is suspended. When the buoyant force is less than the weight, the object sinks. || **Figure 11** The weight and buoyant force determines if an object sinks or floats. **A** The metal cube sinks because its weight is greater than the buoyant force. **B** Equal forces acting on this submerged cube allow it to be suspended in the fluid. **C** The partially submerged wood cube floats at a depth where the buoyant force and weight are equal. || An object that has the same density as the fluid it is submerged in will be <span style="color: rgb(247, 24, 24)">suspended (it will float at any level) in the fluid.
 * [[image:http://www.pearsonsuccessnet.com/ebook/products/0-13-069977-2/hsp00494c04.jpg]] ||  ||

<span style="color: rgb(244, 42, 42)"> Sinking If the shape of a ship's hull allows it to float, what causes a ship to sink?
 * As you know, when the ship's weight becomes greater than the buoyant force acting on it, the ship will sink.
 * This may occur when the ship damages its hull and takes on water.
 * As water enters the hull, the ship displaces less water and the buoyant force decreases.
 * If the damage is not fixed, the ship will eventually sink.

<span style="color: rgb(239, 31, 31)">Floating You may be wondering why a piece of steel sinks, whereas a huge steel ship floats.
 * A heavy steel ship floats because of the shape of its hull.
 * The hull is shaped so that it displaces a large volume of water, creating a large buoyant force.
 * The buoyant force created by the ship's hull is large enough to counteract the ship's tremendous weight.