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Table of Contents. Pressure Floating and Sinking Pascal’s Principle Bernoulli’s Principle. - Pressure. What Is Pressure?. Pressure decreases as the area over which a force is distributed increases.

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Table of contents

Table of Contents

  • Pressure

  • Floating and Sinking

  • Pascal’s Principle

  • Bernoulli’s Principle


What is pressure

- Pressure

What Is Pressure?

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


Table of contents

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.

- Pressure

Area


Table of contents

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

- Pressure

Area


Fluid pressure

- Pressure

Fluid Pressure

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


Variations in fluid pressure

- Pressure

Variations in Fluid Pressure

  • As your elevation increases, atmospheric pressure decreases.


Variations in fluid pressure1

- Pressure

Variations in Fluid Pressure

  • Water pressure increases as depth increases.


Previewing visuals

- Pressure

Previewing Visuals

  • 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.


End of section pressure

End of Section:Pressure


Buoyancy

- Floating and Sinking

Buoyancy

  • Water and other fluids exert an upward force called the buoyant force on any submerged object

  • The pressure on the bottom of a submerged object is greater than the pressure on the top

  • This is due to increasing pressure with increasing depth in a fluid (water)

  • The result is a net force in the upward direction or opposite gravity


Buoyancy1

- Floating and Sinking

Buoyancy

  • If an object’s weight is greater than the buoyant force acting on it then it will sink!

  • An object will float if the buoyant force acting on the object is greater than the weight of the object

  • A submerged object whose weight is equal to the buoyant force has no net force acting on it and will not sink either!


Archimedes principle

Archimedes’ Principle

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


Buoyancy2

- Floating and Sinking

Buoyancy

  • Displacement refers to the movement of an object from its original location.

  • In this case we are referring to the displacement of fluid!


Oasis of the seas

OASIS OF THE SEAS!


Table of contents

  • So how does a cruise ship like the Queen of the Seas stay afloat?

  • Remember that the buoyant force equals the weight of the displace fluid for an object

  • Larger size objects have a greater buoyant force acting on them than smaller objects do because they displace more fluid (even if they are the same weight)

  • A ship floats on the surface as long as the buoyant force acting on it is equal to its weight!


Buoyancy3

- Floating and Sinking

Buoyancy

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


Density mass per unit volume

Density = mass per unit volume


Density

- Floating and Sinking

Density

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


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.


Density1

- Floating and Sinking

Density

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


End of section floating and sinking

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

Hydraulic Devices

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


Hydraulic devices1

- Pascal’s Principle

Hydraulic Devices

  • 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 lifts1

Lift A: 4,000 N; lift B: 2,000 N

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.

- Pascal’s Principle

Comparing Hydraulic Lifts


Comparing hydraulic lifts2

3,000 N

Reading Graphs:

For Lift A, how much force must be applied to lift a 12,000-N object?

- Pascal’s Principle

Comparing Hydraulic Lifts


Comparing hydraulic lifts3

Lift A: applied force is multiplied by four; lift B: applied force is multiplied by two.

Interpreting Data:

By how much is the applied force multiplied for each lift?

- Pascal’s Principle

Comparing Hydraulic Lifts


Comparing hydraulic lifts4

The slope gives the ratio of the lifting force to the applied force. The greater the slope, the more the lift multiplies force.

Interpreting Data:

What can you learn from the slope of the line for each lift?

- Pascal’s Principle

Comparing Hydraulic Lifts


Comparing hydraulic lifts5

Lift A, because it multiplies force more than lift B.

Drawing Conclusions:

Which lift would you choose if you wanted to produce the greater lifting force?

- Pascal’s Principle

Comparing Hydraulic Lifts


Hydraulic brakes

- Pascal’s Principle

Hydraulic Brakes

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


Asking questions

- Pascal’s Principle

Asking Questions

  • 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

End of Section:Pascal’s Principle


Bernoulli s principle

- Bernoulli’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

Applying Bernoulli’s Principle

  • Bernoulli’s principle helps explain how planes fly.


Applying bernoulli s principle1

- Bernoulli’s Principle

Applying Bernoulli’s Principle

  • An atomizer is an application of Bernoulli’s principle.


Applying bernoulli s principle2

- 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 principle3

- Bernoulli’s Principle

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


Links on bernoulli s principle

- Bernoulli’s Principle

Links on Bernoulli’s Principle

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


End of section bernoulli s principle

End of Section:Bernoulli’s Principle


Graphic organizer

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

End of Section:Graphic Organizer


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