1. Chapter 14 Preview Section 1 Fluids and Pressure
Forces in Fluids
Preview
Section 1 Fluids and Pressure
Section 2 Buoyancy and Density
Concept Map

2. Chapter 14
Section 1 Fluids and Pressure
Bellringer
Because water has a higher density than air, a column of water weighs more than a column of air of the same height. The density of air is 1.29 kg/m3 (at 0oC and 1 atm of pressure). The density of water is 1000 kg/m3. Calculate the masses of the following (mass equals density times volume):
1 m3 of air
1 m3 of water
100 m3 of air
100 m3 of water
Write your answers in your Science Journal.

3. Chapter 14 What You Will Learn
Section 1 Fluids and Pressure
What You Will Learn
Pressure is the amount of force exerted on a given area.
Fluid pressure increases as depth increases.
Density is mass per unit volume. Because water is denser than air, water exerts more pressure than air does.
Fluids flow from areas of high pressure to areas of low pressure.

4. Chapter 14 Fluids and Pressure
Section 1 Fluids and Pressure
Fluids and Pressure
A fluid is a nonsolid state of matter in which the atoms or molecules are free to move past each other.
A fluid is any material that can flow and that takes the shape of its container. Liquids and gases are fluids.

5. Fluids and Pressure, continued
Chapter 14
Section 1 Fluids and Pressure
Fluids and Pressure, continued
Pressure is the amount of force exerted on a given area.
Moving particles of matter create pressure by colliding with one another and with the walls of their container.
Fluids exert pressure evenly in all directions.

6. Fluids and Pressure, continued
Chapter 14
Section 1 Fluids and Pressure
Fluids and Pressure, continued
Any force, such as the weight of an object, acting on an area creates pressure.
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).

7. Chapter 14 Atmospheric Pressure
Section 1 Fluids and Pressure
Atmospheric Pressure
The atmosphere is the layer of nitrogen, oxygen, and other gases that surrounds Earth.
The pressure caused by the weight of the atmosphere is called atmospheric pressure.

8. Atmospheric Pressure, continued
Chapter 14
Section 1 Fluids and Pressure
Atmospheric Pressure, continued
The atmosphere extends about 150 km above Earth’s surface. Atmospheric pressure changes as you travel through the atmosphere.
At the top of the atmosphere, pressure is almost nonexistent because there are fewer gas particles and they rarely collide.

9. Chapter 14
Forces in Fluids
Atmospheric Pressure

10. Chapter 14 Water Pressure
Section 1 Fluids and Pressure
Water Pressure
Water is a fluid. So, like the atmosphere, water exerts pressure.
Water pressure increases as the depth of the water increases.
Water pressure depends on depth, not on the total amount of fluid present.

11. Water Pressure, continued
Chapter 14
Section 1 Fluids and Pressure
Water Pressure, continued
A person swimming 3 m below the surface of a small pond feels the same pressure as a person swimming 3 m below the surface of a large lake.
Because water is about 1,000 times denser than air, water exerts more pressure than air does.

12. Pressure Differences and Fluid Flow
Chapter 14
Section 1 Fluids and Pressure
Pressure Differences and Fluid Flow
Fluids flow from areas of high pressure to areas of low pressure.
Differences in air pressure help explain the way your body breathes and the way tornadoes create damaging winds.

13. Chapter 14
Forces in Fluids

14. Chapter 14
Section 2 Buoyancy and Density
Bellringer
Predict whether the following objects will float or sink in water:
an apple
an orange
a penny
a wooden pencil
a nail
List three other objects that will float in water.
Write your answers in your Science Journal.

15. Chapter 14 What You Will Learn
Section 2 Buoyancy and Density
What You Will Learn
All fluids exert an upward force on objects in the fluid.
The buoyant force on an object is equal to the weight of the fluid displaced by the object.
An object will float or sink depending on the relationship between the object’s weight, buoyant force, and overall density.
Density can be calculated from measurements of mass and volume. The overall density of an object can be changed by changing the object’s shape, mass, or volume.

16. Buoyant Force and Fluid Pressure
Chapter 14
Section 2 Buoyancy and Density
Buoyant Force and Fluid Pressure
All fluids exert an upward force called buoyant force.
Buoyant force is the upward force that keeps an object immersed in or floating on a liquid.
Buoyant force is caused by differences in fluid pressure.

17. Chapter 14
Forces in Fluids
Buoyant Force

18. Buoyant Force and Fluid Pressure, continued
Chapter 14
Section 2 Buoyancy and Density
Buoyant Force and Fluid Pressure, continued
A Greek mathematician named Archimedes discovered how to find buoyant force.
Archimedes’ principle states that the buoyant force on an object in a fluid is an upward force equal to the weight of the volume of fluid that the object displaces.

19. Chapter 14
Forces in Fluids

20. Weight Versus Buoyant Force
Chapter 14
Section 2 Buoyancy and Density
Weight Versus Buoyant Force
An object in a fluid will sink if the object’s weight is greater than the buoyant force (the weight of the fluid that the object displaces).
An object floats only when the buoyant force on the object is equal to the object’s weight.

21. Buoyant Force on Floating Objects
Chapter 14
Forces in Fluids
Buoyant Force on Floating Objects

22. Chapter 14 Density and Floating Density is mass per unit volume.
Section 2 Buoyancy and Density
Density and Floating
Density is mass per unit volume.
Any object that is denser than the surrounding fluid will sink.
An object that is less dense than the surrounding fluid will float.

23. Chapter 14 Determining Density
Section 2 Buoyancy and Density
Determining Density
To determine the density of an object, you need to know the object’s mass and volume.
A balance can be used to find the mass of an object.
To find the volume of a regular solid, such as a cube, multiply the lengths of the three sides together.

24. Determining Density, continued
Chapter 14
Section 2 Buoyancy and Density
Determining Density, continued
To find the volume of an irregular solid, use water displacement.
By measuring the volume of water that the object displaces, or pushes aside, you find the volume of the object itself.

25. Changing Overall Density
Chapter 14
Section 2 Buoyancy and Density
Changing Overall Density
The overall density of an object can be changed by changing the object’s shape, mass, or volume.
Submarines use ballast tanks to change their overall density and dive under water.
As water is added to the tanks, the submarine’s mass increases, but its volume stays the same.

26. Changing Overall Density, continued
Chapter 14
Section 2 Buoyancy and Density
Changing Overall Density, continued
Most bony fishes have an organ called a swim bladder that allows them to adjust their overall density.
An inflated swim bladder increases the fish’s volume, which decreases the fish’s overall density so the fish does not sink.

27. Chapter 14
Forces in Fluids

28. Chapter 14
Forces in Fluids
Concept Map
Use the terms below to complete the concept map on the next slide.
depth
density
water pressure
pressure
atmospheric pressure
fluids
water

29. Chapter 14
Forces in Fluids
Concept Map

30. Chapter 14
Forces in Fluids
Concept Map