1. Ch 7 Forces in fluids

2. I. Fluids and Pressure A. Fluids exert pressure
Fluid= any material that can flow and that takes the shape of the container
Liquids & gasses
Molecules move easily past each other
pressure: amount of force exerted on a given area
Pressure = force
area
Measured in Pascal's
1Pa = 1 N/m2
What is the pressure exerted by a book that has an area of 0.2m2 and a weight of 10N Pressure= force area= force F= P x A
area pressure
P = 10N = 50N/m2 or 50 Pa
0.2m2
Do 1 & 2 pg 181 

3. Fluids exert pressure evenly in all directions
When you blow a bubble it gets rounder not just longer

4. B. Atmospheric Pressure
Atmospheric pressure= weight of the atmosphere being pulled to Earth by gravity
Nitrogen most abundant gas ~78%
Oxygen = ~20%
At sea level there is about 101,300 Pa or 101,300 N of pressure on every square inch of your body
2lbs per square cm
15lbs per square inch
Pressure inside your body is also exerting a force out= why we don’t “crush”

5. ~80% of the Earth’s atmosphere is within 10km of Earth
Fewer molecules on top of you as you move up
Mt Everest= highest point on Earth has the air pressure of 33kPa
Sea Level has 101kPa
Pressure and altitude are inversely proportional
Your ears “pop” to adjust to the pressure changes when traveling at different altitudes

6. C. Water pressure Water is a fluid so it exerts pressure like air does
Deeper you go the more water molecules are on top of you the greater the pressure
Total amount of water does not matter- 12 ft deep in a lake is the same as 12 ft deep in a small pool
Water is about 1000 times more dense than air
Density= amount of matter in a given volume
Climbing 10m is not noticeable on land but diving 10m into water would be 2x the pressure as air pressure at sea level

7. D. Pressure differences and fluid flow https://youtu.be/I_auLy036U8
Fluid flow from high pressure to low pressure
Using a straw you take air out of the straw creating a low pressure causing the liquid to move from high pressure to low pressure
Breathing involves creating low and high areas of pressure
Diaphragm flattens creating a larger space in your lungs and a lower pressure= air moves in
Diaphragm relaxes curving upward causing less space and a higher pressure and air moves out
Very low air pressure inside a tornado causes it to act like a giant vacuum

8. II. Buoyant Force A. Buoyant Force and Fluid Pressure https://youtu
Buoyant force= the upward forces that keeps an object immersed in or floating on a liquid
Pressure is exerted on all sides of an immersed object
Pressure on the top increases with depths
Archimedes= Greek mathematician from the 3rd century, discovered how to determine buoyant force
Archimedes principle= 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

9. B. Weight vs Buoyant Force
An object will sink if its weight is greater than the buoyant force (fluid that it displaces)
Rock weighs 75N
Rock displaces 5L ( 50N) of water
Rocks weight is greater than the buoyant force so it will sink
An object will float if its weight is equal to the buoyant force of the fluid
Fish weighs 12 N
Fish displaces 1.2 L (12N) of water
Fish floats suspended in water

10. Something is buoyed up if the buoyant force on the object is greater than the object’s weight
Duck floats on the surfaces because only the ducks feet, legs and stomach have to be underwater to displace 9N which is equal to the dicks weight
If the duck dove under water it would displace more than the 9N and the buoyant force would be greater than the weight & will be pushed up out of the water

11. C. Floating, Sinking & Density
Density – mass per unit volume
D = M ÷ V
The object has to be less dense than the fluid
Ice cube is less dense than water so it floats
Helium is less dense (1/17th) than air so when an object is filled with helium it will float
Find the density of a rock that has a mass of 10 g and a volume of 2 cm3
D = m÷v
D = 10 g = 5g⁄cm3
2 cm3
Do 1-3page 188
NOTE= 1ml = 1 cm3

12. D. Changing overall density
Increasing the volume of an object will decrease the overall density
How steal ships float- increasing the volume of the steal makes the overall density of the ship less than water
Changing mass will cause an object to float or sink
Ballast tanks on a sub can fill with air to float or water to sink
Submarines mass will increase with water but the overall volume stays the same

13. Swim bladder= organ in most boney fish that will increase or decrease the overall volume of the fish to allow it to float
Controlled by the nervous system
Takes gases out of the blood circulation to fill
Sharks do not have a swim bladder so they must constantly move or they will sink

14. III. Fluids in Motion A. Fluid Speed and Pressure
Bernoulli’s principle= states that as a speed of a moving fluid increases , the fluids pressure decreases
Daniel Bernoulli= Swiss mathematician
The area of higher pressure will “push” into the area of lower pressure

15. B. Factors that Affect Flight https://youtu.be/5ltjFEei3AI
Planes can lift off of the ground because of Bernoulli’s principle
The fast-moving air above the wing exerts less pressure than the slow- moving air below the wing
Greater pressure under the wing exerts an upward force
Lift= an upward force on an object that moves in a fluid
Moves against gravity

16. The larger the planes wings the greater the lift
Thrust= the pushing or pulling force exerted by the engine of an aircraft
Faster the speed of the plane- the faster the air moves around the wing - which increases lift
The larger the planes wings the greater the lift
Jet planes have large engines to create great speeds around the wings so the wings can be smaller

17. The larger a birds wing the less it has to flap to create lift
Large wings allows it to ride on air currents
Differences in air pressure will also allow a pitcher to pitch a screwball
Because of the spin of the ball
The left side has a higher pressure causing the ball to move toward the lower right side pressure

18. C. Drag and motion in Fluids
Drag= the force that restricts or opposes motion in a fluid
Trying to walk through a strong wind “drags” your body so its difficult to move forward
Airplanes experience drag from the gaseous fluid of the atmosphere
Turbulence= irregular or unpredictable flow of fluids
Planes use wind flaps on the wings to reduce the amount of drag caused by turbulence

19. D. Pascal's Principle
Pascal’s principle= states that a change in pressure at any point in an enclosed fluid will be transmitted equally to all parts of that fluid
Basal Pascal= 17th century French scientist
Hydraulic devices use Pascal’s Principle to move heavy objects
Liquids cannot be easily compressed
Hydraulic devices multiply forces
Car breaks are an example of Pascal's principle
Driver’s foot pushes on a cylinder of liquid
That pressure is transmitted to larger pistons of the braking system which causes the friction to stop the car