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Resources Chapter Presentation Bellringers Image Bank Standards Assessment Visual Concepts Math Focus

Forces in Fluids Chapter 14 Table of Contents Section 1 Fluids and Pressure Section 2 Buoyancy and Density

Section 1 Fluids and Pressure Chapter 14 Bellringer Because water has a higher density than air, a column of water weighs more than a column of air of the same height. The density of air is 1.29 kg/m3 (at 0oC and 1 atm of pressure). The density of water is 1000 kg/m3. Calculate the masses of the following (mass equals density times volume): • 1 m3 of air • 1 m3 of water • 100 m3 of air • 100 m3 of water Write your answers in your Science Journal.

Section 1 Fluids and Pressure Chapter 14 What You Will Learn • Pressure is the amount of force exerted on a given area. • Fluid pressure increases as depth increases. • Density is mass per unit volume. Because water is denser than air, water exerts more pressure than air does. • Fluids flow from areas of high pressure to areas of low pressure.

Section 1 Fluids and Pressure Chapter 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.

Section 1 Fluids and Pressure Chapter 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.

Section 1 Fluids and Pressure Chapter 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).

Section 1 Fluids and Pressure Chapter 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.

Section 1 Fluids and Pressure Chapter 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.

Forces in Fluids Chapter 14 Atmospheric Pressure

Section 1 Fluids and Pressure Chapter 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.

Section 1 Fluids and Pressure Chapter 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.

Section 1 Fluids and Pressure Chapter 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.

Forces in Fluids Chapter 14

Section 2 Buoyancy and Density Chapter 14 Bellringer Predict whether the following objects will float or sink in water: • an apple • an orange • a penny • a wooden pencil • a nail List three other objects that will float in water. Write your answers in your Science Journal.

Section 2 Buoyancy and Density Chapter 14 What You Will Learn • All fluids exert an upward force on objects in the fluid. • The buoyant force on an object is equal to the weight of the fluid displaced by the object. • An object will float or sink depending on the relationship between the object’s weight, buoyant force, and overall density. • Density can be calculated from measurements of mass and volume. The overall density of an object can be changed by changing the object’s shape, mass, or volume.

Section 2 Buoyancy and Density Chapter 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.

Forces in Fluids Chapter 14 Buoyant Force

Section 2 Buoyancy and Density Chapter 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.

Section 2 Buoyancy and Density Chapter 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.

Forces in Fluids Chapter 14 Buoyant Force on Floating Objects

Section 2 Buoyancy and Density Chapter 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.

Section 2 Buoyancy and Density Chapter 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.

Section 2 Buoyancy and Density Chapter 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.

Section 2 Buoyancy and Density Chapter 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.

Section 2 Buoyancy and Density Chapter 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.

Forces in Fluids Chapter 14 Concept Map Use the terms below to complete the concept map on the next slide.

Forces in Fluids Chapter 14 Concept Map

Forces in Fluids Chapter 14 End of Chapter 14 Show

Standards Assessment Chapter 14 1. Chooses the appropriate form of the word displace for the following sentence: “When the volume of an object is not easily calculated, you can find the object’s volume by using _____.” A. displace B. displacing C. displacement D. displaced

Standards Assessment Chapter 14 2. Which of the following words is closest in meaning to the word predict? A. apply B. explain C. say ahead of time D. identity

Standards Assessment Chapter 14 3. In the sentence “The weight of the displaced water is equal to the buoyant force acting on the object,” what does the word displaced mean? A. assigned to B. moved aside C. changed D. adapted to

Standards Assessment Chapter 14 4. Which of the following words means “the amount of space that an object contains or takes up”? A. width B. length C. force D. volume

Standards Assessment Chapter 14 5. Which procedure allows you to determine the volume of an irregularly shaped object? A. Divide the density of the object by the mass of the object. B. Calculate the water pressure around the object. C. Measure the amount of water displaced by the object. D. Multiply the width, length, and height of the object.

Standards Assessment Chapter 14 6. Which of the following is the correct way to find the density of an object? A. Divide the mass of the object by the volume of the object. B. Multiply the mass of the object by the volume of the object. C. Measure the buoyant force that is acting on the object. D. Measure the weight of the water displaced by the object.

Standards Assessment Chapter 14 Use the table below to answer the next question.

Standards Assessment Chapter 14 7. The table above shows mass and volume measurements for four objects. Which of these objects will float in water, given that the density of liquid water is 1 g/cm3? A. Object 1 B. Object 2 C. Object 3 D. Object 4

Standards Assessment Chapter 14 8. A submarine can travel on the surface of water and underwater. How does a submarine dive underwater? A. Water is added to special tanks in the submarine to increase its mass and therefore its overall density. B. Air is released from special tanks in the submarine to increase its volume. C. Special mechanisms change the submarine’s shape and allow it to dive. D. The density of the submarine increases and the water pressure decreases when it dives.

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