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**Chapter 7 Preview Section 1 Fluids and Pressure**

Forces in Fluids Preview Section 1 Fluids and Pressure Section 2 Buoyant Force Section 3 Fluids and Motion Concept Mapping

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**Chapter 7 Bellringer Imagine the following situation:**

Section 1 Fluids and Pressure Bellringer Imagine the following situation: One afternoon, you go outside to find your younger sister standing by her bike with a nail in her hand. The bike has a flat tire. She wants to know why the air came out of the tire when she pulled the nail out. Write a few sentences in you science journal to explain why air rushes out of a hole in a tire.

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**Chapter 7 Objectives Describe how fluids exert pressure.**

Section 1 Fluids and Pressure Objectives Describe how fluids exert pressure. Analyze how atmospheric pressure varies with depth. Explain how depth and density affect water pressure. Give examples of fluids flowing from high to low pressure.

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**Chapter 7 Fluids Exert Pressure**

Section 1 Fluids and Pressure Fluids Exert Pressure A fluid is any material that can flow and that takes the shape of its container. Fluids include liquids and gases. All fluids exert pressure, which is the amount of force exerted per unit area of a surface.

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**Fluids Exert Pressure, continued**

Chapter 7 Section 1 Fluids and Pressure Fluids Exert Pressure, continued In the image below, the force of the air particles hitting the inner surface of the tire creates pressure, which keeps the tire inflated.

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**Chapter 7 Pressure Section 1 Fluids and Pressure**

Click below to watch the Visual Concept. Visual Concept

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**Fluids Exert Pressure, continued**

Chapter 7 Section 1 Fluids and Pressure Fluids Exert Pressure, continued Calculating Pressure Pressure can be calculated by using the following equation: pressure = force area 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).

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**Pressure, Force, and Area**

Chapter 7 Section 1 Fluids and Pressure Pressure, Force, and Area

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**Fluids Exert Pressure, continued**

Chapter 7 Section 1 Fluids and Pressure Fluids Exert Pressure, continued Pressure and Bubbles Soap bubbles get rounder as they get bigger because fluids exert pressure evenly in all directions. Since air is a fluid, adding air to an air bubble causes it to expand in all directions at once.

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**Chapter 7 Atmospheric Pressure**

Section 1 Fluids and Pressure Atmospheric Pressure The atmosphere is the thin layer of nitrogen, oxygen, and other gases that surrounds Earth. Atmospheric pressure is the pressure caused by the weight of the atmosphere. Atmospheric pressure is exerted on everything on Earth, including you.

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**Atmospheric Pressure, continued**

Chapter 7 Section 1 Fluids and Pressure Atmospheric Pressure, continued The air inside this balloon exerts pressure that keeps the balloon inflated against atmospheric pressure.

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**Atmospheric Pressure, continued**

Chapter 7 Section 1 Fluids and Pressure Atmospheric Pressure, continued Variation of Atmospheric Pressure The atmosphere stretches about 150 km above the Earth’s surface, but about 80% of the atmosphere’s gases are found within 10 km. At the top of the atmosphere, pressure is almost nonexistent. Atmospheric Pressure and Depth As you travel through the atmosphere, atmospheric pressure changes. The further down through the atmosphere you go, the greater the pressure is.

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**Atmospheric Pressure, continued**

Chapter 7 Section 1 Fluids and Pressure Atmospheric Pressure, continued Pressure Changes and Your Body If you travel to higher or lower points in the atmosphere, the fluids in your body have to adjust to maintain equal pressure. You may have experienced this adjustment is your ears have “popped” when you were in a plane taking off or in a car traveling down a steep mountain road.

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**Chapter 7 Water Pressure**

Section 1 Fluids and Pressure Water Pressure Water is a fluid. So, it exerts pressure like the atmosphere does. Water Pressure and Depth Like atmospheric pressure, water pressure depends on depth. Density Makes a Difference Because water is more dense than air, a certain volume of water has more mass—and weighs more—than the same volume of air. Water exerts more pressure than air.

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**Pressure Differences and Fluid Flow**

Chapter 7 Section 1 Fluids and Pressure Pressure Differences and Fluid Flow Just by drinking through a straw you can observe an important property of fluids: Fluids flow from areas of high pressure to areas of low pressure. Pressure Difference and Breathing The next slide shows how exhaling causes fluids to flow from high to low pressure.

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Chapter 7 Section 1 Fluids and Pressure

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**Pressure Differences and Fluid Flow, continued**

Chapter 7 Section 1 Fluids and Pressure Pressure Differences and Fluid Flow, continued Pressure Differences and Tornadoes The air pressure inside a tornado is very low. Because the air pressure outside of the tornado is higher than the pressure inside, air rushes into the tornado. The rushing air causes the tornado to be like a giant vacuum cleaner.

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Chapter 7 Section 2 Buoyant Force Bellringer Identify which of the following objects will float in water: a rock, an orange, a screw, a quarter, a candle, a plastic-foam “peanut,” and a chalkboard eraser. Write a hypothesis in your science journal about why an aircraft carrier, which weighs thousands of tons, does not sink.

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Chapter 7 Section 2 Buoyant Force Objectives Explain the relationship between fluid pressure and buoyant force. Predict whether an object will float or sink in a fluid. Analyze the role of density in an object’s ability to float. Explain how the overall density of an object can be changed.

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**Buoyant Force and Fluid Pressure**

Chapter 7 Section 2 Buoyant Force Buoyant Force and Fluid Pressure Buoyant force is the upward force that keeps an object immersed in or floating on a liquid. Determining Buoyant Force Archimedes’ principle states that the buoyant force on an object is an upward force equal to the weight of the fluid that the object takes the place of, or displaces.

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**Buoyant Force and Fluid Pressure, continued**

Chapter 7 Section 2 Buoyant Force Buoyant Force and Fluid Pressure, continued There is more pressure at the bottom of an object because pressure increases with depth. This results in an upward buoyant force on the object.

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**Weight Versus Buoyant Force**

Chapter 7 Section 2 Buoyant Force Weight Versus Buoyant Force Sinking An object in a fluid will sink if its weight is greater than the buoyant force. Floating An object will float only when the buoyant force on the object is equal to the object’s weight. Buoying Up When the buoyant force on an object is greater than the object’s weight, the object is buoyed up (pushed up) in water.

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**Weight Versus Buoyant Force, continued**

Chapter 7 Section 2 Buoyant Force Weight Versus Buoyant Force, continued Will an object sink or float? That depends on the whether the buoyant force is less than or equal to the object’s weight.

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**Buoyant Force on Floating Objects**

Chapter 7 Section 2 Buoyant Force Buoyant Force on Floating Objects Click below to watch the Visual Concept. Visual Concept

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**Floating, Sinking, and Density**

Chapter 7 Section 2 Buoyant Force Floating, Sinking, and Density More Dense Than Air Ice floats on water because it is less dense than water. Ice, like most substances, is more dense than air. So, ice does not float in air. Less Dense Than Air One substance that is less dense than air is helium gas. A given volume of helium displaces an equal volume of air that is much heavier than itself. So, helium floats in air.

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Chapter 7 Section 2 Buoyant Force Finding Density

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**Changing Overall Density**

Chapter 7 Section 2 Buoyant Force Changing Overall Density Changing Shape The secret of how a ship floats is in the shape of the ship. Ships made of steel float because their overall density is less than the density of water. The next slide demonstrates how a ship made out of steel, which is almost 8 times denser than water, is able to float in water.

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Chapter 7 Section 2 Buoyant Force

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**Changing Overall Density, continued**

Chapter 7 Section 2 Buoyant Force Changing Overall Density, continued Changing Mass A submarine is a special kind of ship that can travel both on the surface of the water and underwater. Submarines have ballast tanks that can be opened to allow sea water to flow in. As water is added, the submarine’s mass increases, but its volume stays the same.

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Chapter 7 Section 2 Buoyant Force

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**Changing Overall Density, continued**

Chapter 7 Section 2 Buoyant Force Changing Overall Density, continued Changing Volume Like a submarine, some fish adjust their overall density to stay at a certain depth in the water. Most bony fishes have an organ called a swim bladder which helps them change volume.

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**Chapter 7 Swim Bladder Section 2 Buoyant Force**

Click below to watch the Visual Concept. Visual Concept

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Chapter 7 Section 3 Fluids and Motion Bellringer You have been asked to design two kites. One kite will be flown in areas where there is almost always a good breeze. The other kite will be flown in areas with very little wind. What differences in design and materials are there between your two kites? Record your designs in your science journal.

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Chapter 7 Section 3 Fluids and Motion Objectives Describe the relationship between pressure and fluid speed. Analyze the roles of lift, thrust, and wing size in flight. Explain Pascal’s principle. Describe drag, and explain how it affects lift.

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**Fluid Speed and Pressure**

Chapter 7 Section 3 Fluids and Motion Fluid Speed and Pressure Bernoulli’s principle states that as the speed of a moving fluid increases, the fluid’s pressure decreases. Science in a Sink A table-tennis ball is attached to a string and swung into a stream of water, where it is held. Because the water is moving faster than air, the ball is pushed by the higher pressure of the air into an area of reduced pressure—the water stream.

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**Factors That Affect Flight**

Chapter 7 Section 3 Fluids and Motion Factors That Affect Flight Thrust and Lift Thrust is the forward force produced by a plane’s engine. Lift is the upward force on the wing as it moves through the air. Wing Size, Speed, and Lift Smaller wings keep a plane’s weight low, which also helps it move faster. Bernoulli and Birds A small bird must flap its small wings at a fast pace to stay in the air, but a large bird flaps less.

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Chapter 7 Section 3 Fluids and Motion

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**Factors That Affect Flight, continued**

Chapter 7 Section 3 Fluids and Motion Factors That Affect Flight, continued Bernoulli and Baseball The next slide shows how a baseball pitcher can take advantage of Bernoulli’s principle to throw a curveball.

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Chapter 7 Section 3 Fluids and Motion

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**Drag and Motion in Fluids**

Chapter 7 Section 3 Fluids and Motion Drag and Motion in Fluids Drag is the force that opposes or restricts motion in a fluid. It is a force that is parallel to the velocity of the flow. Drag is usually caused by an irregular flow of air, known as turbulence. Turbulence and Lift Lift is often reduced when turbulence causes drag.

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**Chapter 7 Pascal’s Principle**

Section 3 Fluids and Motion Pascal’s Principle What Is Pascal’s Principle? Pascal’s principle states that a change in pressure at any point in an enclosed fluid will be transmitted equally to all parts of that fluid. Pascal’s Principle and Motion Hydraulic devices use Pascal’s principle to move or lift objects. Liquids are used in hydraulic devices because liquids cannot be easily compressed into a smaller space.

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**Pascal’s Principle, continued**

Chapter 7 Section 3 Fluids and Motion Pascal’s Principle, continued Because of Pascal’s principle, the touch of a foot can stop tons of moving metal.

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**Chapter 7 Concept Mapping**

Forces in Fluids Concept Mapping Use the terms below to complete the Concept Mapping on the next slide. depth density water pressure pressure fluids water atmospheric pressure

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Chapter 7 Forces in Fluids

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Chapter 7 Forces in Fluids

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