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**Table of Contents Pressure Floating and Sinking Pascal’s Principle**

Bernoulli’s Principle

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**What Is Pressure? - Pressure**

Pressure decreases as the area over which a force is distributed increases.

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- Pressure Area The area of a surface is the number of square units that it covers. To find the area of a rectangle, multiply its length by its width. The area of the rectangle below is 2 cm X 3 cm, or 6 cm2.

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**Area - Pressure Practice Problem**

Which has a greater area: a rectangle that is 5 cm X 20 cm or a square that is 10 cm X 10 cm? Both have the same area, 100 cm2. 5 cm X 20 cm = 100 cm2 10 cm X 10 cm = 100 cm2

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**Fluid Pressure - Pressure**

All of the forces exerted by the individual particles in a fluid combine to make up the pressure exerted by the fluid.

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**Variations in Fluid Pressure**

As your elevation increases, atmospheric pressure decreases.

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**Variations in Fluid Pressure**

Water pressure increases as depth increases.

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**Previewing Visuals - Pressure**

Before you read, preview Figure 5. Then write two questions that you have about the diagram in a graphic organizer like the one below. As you read, answer your questions. Pressure Variations Q. Why does the pressure change with elevation and depth? A. Air and water exert pressure, so pressure varies depending on how much air or water is above you. Q. How much greater is water pressure at a depth of 6,500 m than it is at sea level? A. It is about 650 times greater.

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**Links on Fluids and Pressure**

Click the SciLinks button for links on fluids and pressure.

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**End of Section: Pressure**

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**Buoyancy - Floating and Sinking**

The pressure on the bottom of a submerged object is greater than the pressure on the top. The result is a net force in the upward direction.

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**Buoyancy - Floating and Sinking**

The buoyant force acts in the direction opposite to the force of gravity, so it makes an object feel lighter.

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**Buoyancy - Floating and Sinking**

Achimedes’ principle states that the buoyant force acting on a submerged object is equal to the weight of the fluid the object displaces.

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**Buoyancy - Floating and Sinking**

A solid block of steel sinks when placed in water. A steel ship with the same weight floats.

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**Density - Floating and Sinking**

Changes in density cause a submarine to dive, rise, or float.

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**Relating Cause and Effect**

- Floating and Sinking Relating Cause and Effect As you read, identify the reasons why an object sinks. Write them down in a graphic organizer like the one below. Causes Weight is greater than buoyant force. Effect Object is denser than fluid. Object sinks. Object takes on mass and becomes denser than fluid. Object is compressed and becomes denser than fluid.

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**Click the Video button to watch a movie about density.**

- Floating and Sinking Density Click the Video button to watch a movie about density.

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**End of Section: Floating and Sinking**

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**Transmitting Pressure in a Fluid**

- Pascal’s Principle Transmitting Pressure in a Fluid When force is applied to a confined fluid, the change in pressure is transmitted equally to all parts of the fluid.

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**Hydraulic Devices - Pascal’s Principle**

In a hydraulic device, a force applied to one piston increases the fluid pressure equally throughout the fluid.

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**Hydraulic Devices - Pascal’s Principle**

By changing the size of the pistons, the force can be multiplied.

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**Hydraulic Systems Activity**

- Pascal’s Principle Hydraulic Systems Activity Click the Active Art button to open a browser window and access Active Art about hydraulic systems.

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**Comparing Hydraulic Lifts**

- Pascal’s Principle Comparing Hydraulic Lifts In the hydraulic device in Figure 15, a force applied to the piston on the left produces a lifting force in the piston on the right. The graph shows the relationship between the applied force and the lifting force for two hydraulic lifts.

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**Comparing Hydraulic Lifts**

- Pascal’s Principle Comparing Hydraulic Lifts Reading Graphs: Suppose a force of 1,000 N is applied to both lifts. Use the graph to determine the lifting force of each lift. Lift A: 4,000 N; lift B: 2,000 N

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**Comparing Hydraulic Lifts**

- Pascal’s Principle Comparing Hydraulic Lifts Reading Graphs: For Lift A, how much force must be applied to lift a 12,000-N object? 3,000 N

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**Comparing Hydraulic Lifts**

- Pascal’s Principle Comparing Hydraulic Lifts Interpreting Data: By how much is the applied force multiplied for each lift? Lift A: applied force is multiplied by four; lift B: applied force is multiplied by two.

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**Comparing Hydraulic Lifts**

- Pascal’s Principle Comparing Hydraulic Lifts Interpreting Data: What can you learn from the slope of the line for each lift? The slope gives the ratio of the lifting force to the applied force. The greater the slope, the more the lift multiplies force.

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**Comparing Hydraulic Lifts**

- Pascal’s Principle Comparing Hydraulic Lifts Drawing Conclusions: Which lift would you choose if you wanted to produce the greater lifting force? Lift A, because it multiplies force more than lift B.

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**Hydraulic Brakes - Pascal’s Principle**

The hydraulic brake system of a car multiplies the force exerted on the brake pedal.

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**Asking Questions - Pascal’s Principle**

Before you read, preview the red headings. In a graphic organizer like the one below, ask a what or how question for each heading. As you read, write answers to your questions. Question Answer How is pressure transmitted in a fluid? Pressure is transmitted equally to all parts of the fluid. What is a hydraulic system? A hydraulic system uses a confined fluid to transmit pressure.

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**End of Section: Pascal’s Principle**

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**Bernoulli’s Principle**

Bernoulli’s principle states that as the speed of a moving fluid increases, the pressure within the fluid decreases.

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**Applying Bernoulli’s Principle**

Bernoulli’s principle helps explain how planes fly.

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**Applying Bernoulli’s Principle**

An atomizer is an application of Bernoulli’s principle.

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**Applying Bernoulli’s Principle**

Thanks in part to Bernoulli's principle, you can enjoy an evening by a warm fireplace without the room filling up with smoke.

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**Applying Bernoulli’s Principle**

Like an airplane wing, a flying disk uses a curved upper surface to create lift.

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**Identifying Main Ideas**

- Bernoulli’s Principle Identifying Main Ideas As you read the section “Applying Bernoulli’s Principle,” write the main idea in a graphic organizer like the one below. Then write three supporting details that further explain the main idea. Main Idea Bernoulli’s principle is a factor that helps explain… Detail Detail Detail how airplanes fly why smoke rises up a chimney how an atomizer works

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**Links on Bernoulli’s Principle**

Click the SciLinks button for links on Bernoulli’s principle.

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**End of Section: Bernoulli’s Principle**

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**How a Hydraulic Device Works**

Graphic Organizer How a Hydraulic Device Works Force is applied to a small piston. Pressure in a confined fluid is increased. The pressure is transmitted equally throughout the fluid. The confined fluid presses on a piston with a larger surface area. The original force is multiplied.

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**End of Section: Graphic Organizer**

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