1. Chapter 3: Forces in Fluids

2. Section 1: Fluid and Pressure
Fluid: any material that can flow and takes the shape of its container
Examples: liquid, gases
Particles in fluids are able to slip by each other—allows them to take on container shape

3. All Fluids Exert Pressure
Pressure: amount of force exerted on a given area
Pressure = Force/area
Pascal: SI unit for pressure

4. Fluid Pressure
All of the forces exerted by the individual molecules in a fluid add together to make up the pressure exerted by the fluid.

5. Why Are Bubbles Round?
Fluid exerts pressure evenly in all directions to form sphere

6. Atmospheric Pressure
Atmosphere: layers of Nitrogen, Oxygen, and other gases that surround the earth
Extends to 150 km above surface
80% of gases found within 10km of surface
Held in place by gravity
Atmospheric Pressure: pressure caused by the weight of the atmosphere

7. Pressure Depends on Depth
Pressure increases as you descend (deeper)
Air pressure lessens as elevation increases
More pressure at lower levels
Your body will adjust to movement between higher and lower altitudes will cause your ears to ‘pop’

8. Water Pressure Increases with depth
Depth effects pressure not the size of the body of water

9. Density Makes a Difference
Water is 1000x more dense than air
Density: amount of matter/volume

10. Fluids go from High Pressure to Low Pressure
Examples: liquid through a straw
Example: breathing

11. Pascal’s Principle Blaise Pascal: 17 Century French scientist
Pascal’s Principle: Change in pressure at any point in an enclosed fluid will be transmitted equally to all parts of a fluid

12. Putting Pascal’s Principle to Work
Hydraulic: liquid pressure devise
Pushing on the petal transmits pressure to brake pads

13. Section 2
Upward force that fluids exert on all matter

14. Buoyant Force is Caused by Differences in Fluid Pressure
Side pressures have net force of zero
Because pressure is greater at bottom then at top—there is an upward net force

15. Determining Buoyant Forces
Archimedes—Greek mathematician; 3rd Cent. B.C.
Archimedes’s Principle: Buoyant Force is equal to the upward force; its equal to the weight of the volume of fluid an object displaces
Weight of object not a factor

16. Weight Vs. Buoyant Force
Sink
Weight of object is greater than the weight of the fluid displaced
Float
Weight is equal or less than the weight of the fluid displaced
Buoying Up
If the force is greater than the object’s weight—then the object is pushed up until the weight of the displaced fluid equals the weight of the object

17. An Object Will Float or Sink Based on its Density
More Dense Than Air
Most substances more dense than air and therefore do not float
Ex. Rubber Duckie less dense than water and so it floats in water. The Rubber Duckie is more dense than air and so it does not float in the air.
Less Dense Than Air
Helium is a gas that is less dense than air
Ex. Balloons filled with helium float

18. The Mystery of Floating Steel
Steel is 8x more dense than water and yet steel ships float
Shape
The shape of ships increases it volume
Increase in volume decreases the ships density
The ships overall density is then less than that of the water

19. Density on the Move
Submarines dive because they take on and expel water
How is a Fish Like a Submarine?
The swim bladder can increase/decrease its volume—which increase/decreases the fish’s density

20. Section 3: Bernoulli’s Principle
Daniel Bernoulli: 18th Century Swiss Mathematician
Discovered that increasing the speed of a fluid decreases pressure; faster moving water exerts less pressure

21. It’s a Bird It’s a Plane It’s Bernoulli’s Principle
Science in the Sink
Tennis Balls are kept in the stream of water because the stream has less pressure than the surrounding air
It’s a Bird It’s a Plane It’s Bernoulli’s Principle
Faster moving air above wings exerts less pressure than slower moving air below the wings
Increased pressure below causes and upward force for the wings/lift

22. Thrust and Wing Size Determine Lift
Size of the wing and the speed at which air travels around the wing determines lift
Trust—forward motion produced by engines

23. Bernoulli’s Principle Is For the Birds
Birds Flap wings
Larger wings need to be flapped less than smaller wings for birds to move

24. Drag Opposing Motion in Fluids
Drag—force that opposes or resists motion in a fluid
Turbulence—irregular flow of fluids
Lift is often reduced when turbulence causes drag

25. Wings are Not Always Required
Race cars and Frisbees also demonstrate this principle