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

2. What Is Pressure? - Pressure
Pressure decreases as the area over which a force is distributed increases.

3. - 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.

4. 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

5. 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.

6. Variations in Fluid Pressure
As your elevation increases, atmospheric pressure decreases.

7. Variations in Fluid Pressure
Water pressure increases as depth increases.

8. 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.

9. End of Section: Pressure

10. Buoyancy - Floating and Sinking
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

11. - 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!

12. 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.

13. - 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!

14. OASIS OF THE SEAS!

15. 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!

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

17. Density = mass per unit volume

20. Density - Floating and Sinking
Changes in density cause a submarine to dive, rise, or float.

21. 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.

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

23. End of Section: Floating and Sinking

24. 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.

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

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

27. 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.

28. 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.

29. 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

30. 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

31. 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.

32. 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.

33. 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.

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

35. 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.

36. End of Section: Pascal’s Principle

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

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

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

40. 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.

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

42. 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

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

44. End of Section: Bernoulli’s Principle

45. 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.

46. End of Section: Graphic Organizer