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

What Is Pressure? - Pressure A force exerted over an area on the surface of an object. Pressure decreases as the area over which a force is distributed increases.

Formula for Pressure Pressure = Force / Area SI Unit: N/m2 or Pascal **Calculate the pressure on a man’s foot when a woman who weighs 130 lb steps on his foot with her heel which has an area of 0.5 in2 with all her weight. Pressure = Force / Area Force = 130 lbs Area = 0.5 in2 Pressure = 130 lbs / 0.5 in2 = 260 lbs/in2 How do you find area? Length x width + answer is in unit squared!!!

Try another one!! Calculate the pressure exerted on an elevator floor which is 2 meters deep and 3 meters wide, if the combined weight standing on it is 1500N. Pressure = Force/Area Force = 1500N Area = 2m x 3m = 6m2 Pressure = 1500N / 6m2 = 250 N/m2

- 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.

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

Fluid Pressure - Pressure Fluid: A material that can easily flow and change shape (liquids or gases) All of the forces exerted by the individual particles in a fluid combine to make up the pressure exerted by the fluid. Total Pressure of the fluid= Total force exerted/ area over which the force is exerted

Variations in Fluid Pressure Air pressure = the weight of air pushing down on us, also called atmospheric pressure At sea level air pressure = 10.13 N/cm2. Air presses down on us from all sides. Forces are balanced therefore we don’t feel it. As your elevation increases, atmospheric pressure decreases.

Variations in Fluid Pressure Water pressure increases as depth increases. Pressure includes the weight of the air + the weight of the water.

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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End of Section: Pressure

Buoyancy - Floating and Sinking Water exerts an upward force called the buoyant force on a submerged object. This is why things feel lighter in water. Buoyant force acts in the opposite direction as gravity.

Buoyancy - Floating and Sinking 2. If the object’s weight is greater than the buoyant force the object will sink.

Buoyancy - Floating and Sinking Archimedes’ principle: The buoyant force acting on a submerged object is equal to the weight of the fluid the object displaces.

Archimedes’ principle If your body displaces 50 L of water, the buoyant force exerted by you is equal to the weight of 50L or 500N. Large objects displace more water therefore increasing buoyant force. Larger objects will float more easily than smaller ones of the same weight. A ship will float as long as the buoyant force acting on it is equal to its weight.

Buoyancy - Floating and Sinking A solid block of steel sinks when placed in water. A steel ship with the same weight floats.

Density - Floating and Sinking 1. Density = Mass / Volume 2. Changes in density changes its ability to sink or float.

In a Submarine-- In a Balloon-- 1)It takes on water in its flotation tank in order to sink. It releases water in order to float. 2) It rises when its weight is less than the buoyant force In a Balloon-- A helium balloon is less dense than a regular balloon.

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.

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

End of Section: Floating and Sinking

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.

Hydraulic Devices - Pascal’s Principle In a hydraulic device, a force applied to one piston increases the fluid pressure equally throughout the fluid.

Hydraulic Devices - Pascal’s Principle By changing the size of the pistons, the force can be multiplied.

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.

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.

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

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

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.

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.

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.

Hydraulic Brakes - Pascal’s Principle The hydraulic brake system of a car multiplies the force exerted on the brake pedal.

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.

End of Section: Pascal’s Principle

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

Applying Bernoulli’s Principle Bernoulli’s principle helps explain how planes fly.

Applying Bernoulli’s Principle An atomizer is an application of Bernoulli’s principle.

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.

Applying Bernoulli’s Principle Like an airplane wing, a flying disk uses a curved upper surface to create lift.

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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End of Section: Bernoulli’s Principle

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.

End of Section: Graphic Organizer