< Back Next > Preview Main

Chapter 14 Forces in Fluids

Preview

Section 1 Fluids and Pressure

Section 2 Buoyancy and Density

Concept Map

< Back Next > Preview Main

Section 1 Fluids and PressureChapter 14

Fluids and Pressure

• A fluid is a nonsolid state of matter in which the atoms or molecules are free to move past each other.

• A fluid is any material that can flow and that takes the shape of its container. Liquids and gases are fluids.

< Back Next > Preview Main

Section 1 Fluids and PressureChapter 14

Fluids and Pressure, continued

• Pressure is the amount of force exerted on a given area.

• Moving particles of matter create pressure by colliding with one another and with the walls of their container.

• Fluids exert pressure evenly in all directions.

< Back Next > Preview Main

Section 1 Fluids and PressureChapter 14

Fluids and Pressure, continued

• Any force, such as the weight of an object, acting on an area creates pressure.

• The SI unit for pressure is the pascal.

• One pascal (1 Pa) is the force of one newton exerted over an area of one square meter (1 N/m2).

< Back Next > Preview Main

Section 1 Fluids and PressureChapter 14

Atmospheric Pressure

• The atmosphere is the layer of nitrogen, oxygen, and other gases that surrounds Earth.

• The pressure caused by the weight of the atmosphere is called atmospheric pressure.

< Back Next > Preview Main

Section 1 Fluids and PressureChapter 14

Atmospheric Pressure, continued

• The atmosphere extends about 150 km above Earth’s surface. Atmospheric pressure changes as you travel through the atmosphere.

• At the top of the atmosphere, pressure is almost nonexistent because there are fewer gas particles and they rarely collide.

< Back Next > Preview Main

Forces in FluidsChapter 14

Atmospheric Pressure

< Back Next > Preview Main

Section 1 Fluids and PressureChapter 14

Water Pressure

• Water is a fluid. So, like the atmosphere, water exerts pressure.

• Water pressure increases as the depth of the water increases.

• Water pressure depends on depth, not on the total amount of fluid present.

< Back Next > Preview Main

Section 1 Fluids and PressureChapter 14

Water Pressure, continued

• A person swimming 3 m below the surface of a small pond feels the same pressure as a person swimming 3 m below the surface of a large lake.

• Because water is about 1,000 times denser than air, water exerts more pressure than air does.

< Back Next > Preview Main

Section 1 Fluids and PressureChapter 14

Pressure Differences and Fluid Flow

• Fluids flow from areas of high pressure to areas of low pressure.

• Differences in air pressure help explain the way your body breathes and the way tornadoes create damaging winds.

< Back Next > Preview Main

Forces in FluidsChapter 14

< Back Next > Preview Main

Section 2 Buoyancy and DensityChapter 14

Buoyant Force and Fluid Pressure

• All fluids exert an upward force called buoyant force.

• Buoyant force is the upward force that keeps an object immersed in or floating on a liquid.

• Buoyant force is caused by differences in fluid pressure.

< Back Next > Preview Main

Forces in FluidsChapter 14

Buoyant Force

< Back Next > Preview Main

Section 2 Buoyancy and DensityChapter 14

Buoyant Force and Fluid Pressure, continued

• A Greek mathematician named Archimedes discovered how to find buoyant force.

• Archimedes’ principle states that the buoyant force on an object in a fluid is an upward force equal to the weight of the volume of fluid that the object displaces.

< Back Next > Preview Main

Forces in FluidsChapter 14

< Back Next > Preview Main

Section 2 Buoyancy and DensityChapter 14

Weight Versus Buoyant Force

• An object in a fluid will sink if the object’s weight is greater than the buoyant force (the weight of the fluid that the object displaces).

• An object floats only when the buoyant force on the object is equal to the object’s weight.

< Back Next > Preview Main

Forces in FluidsChapter 14

Buoyant Force on Floating Objects

< Back Next > Preview Main

Section 2 Buoyancy and DensityChapter 14

Density and Floating

• Density is mass per unit volume.

• Any object that is denser than the surrounding fluid will sink.

• An object that is less dense than the surrounding fluid will float.

< Back Next > Preview Main

Section 2 Buoyancy and DensityChapter 14

Determining Density

• To determine the density of an object, you need to know the object’s mass and volume.

• A balance can be used to find the mass of an object.

• To find the volume of a regular solid, such as a cube, multiply the lengths of the three sides together.

< Back Next > Preview Main

Section 2 Buoyancy and DensityChapter 14

Determining Density, continued

• To find the volume of an irregular solid, use water displacement.

• By measuring the volume of water that the object displaces, or pushes aside, you find the volume of the object itself.

< Back Next > Preview Main

Section 2 Buoyancy and DensityChapter 14

Changing Overall Density

• The overall density of an object can be changed by changing the object’s shape, mass, or volume.

• Submarines use ballast tanks to change their overall density and dive under water.

• As water is added to the tanks, the submarine’s mass increases, but its volume stays the same.

< Back Next > Preview Main

Section 2 Buoyancy and DensityChapter 14

Changing Overall Density, continued

• Most bony fishes have an organ called a swim bladder that allows them to adjust their overall density.

• An inflated swim bladder increases the fish’s volume, which decreases the fish’s overall density so the fish does not sink.

< Back Next > Preview Main

Forces in FluidsChapter 14