Fluid Pressure Chapter 13 Section 1 Page 390

Objectives You should be able to explain what pressure depends on. You should be able to explain how fluids exert pressure. You should be able to describe how fluid pressure changes with elevation and depth.

Fluid Pressure Chapter 13 Section 1 Pg. 390-393

Have you wondered…?

Pressure The result of a _____ distributed over an ____ So… The ______ the area over which the force is distributed, the less pressure is _______. Ex: a pencil point has a much smaller area than the eraser, so it exerts much _______ pressure than the eraser.

Surface Area of my bare feet = 400.0 cm2 Surface Area of my boots = 600.0 cm2 Surface Area of my snowshoes = 3600.0 cm2

Calculating Pressure

Units _____- measured in newtons (N) Area- measured in ______ meters (m2) _______- SI unit is newton per square meter (N/m2) Also called ______ (Pa) 1 N/m2 = 1 Pa Named for French scientist ______ Pascal Pressure is often in ___ 1 kPa = 1,000 Pa

Practice Problem Calculate the pressure produced by a force of 800 N acting on an area of 2.0 m2. P = F/A P = (800 N)/(2.0 m2) P = 400 N/m2 = 400 Pa = 0.4 kPa

Fluids ______ also exert a pressure Fluid is a material that can easily flow Fluids take ____ of container Liquids and ______ are fluids

Cause of Fluid Pressure Fluid particles ______ with a surface, exerting a force on the surface All of the forces exerted combine to make up the ________ exerted by the fluid The ______ of particles in a fluid is large, so a fluid can be considered as a whole.

Fluid Pressure Determined by the ____ of fluid and its depth

Fluid Pressure Water ________ increases as depth increases. The pressure at any given depth is constant, and it is ______ equally in all directions.

Why do ears “pop”?

Air Pressure Earth’s _________ is made up of a mixture gases Atmospheric pressure = 101 kPa at ________ ___ pressure decreases as the altitude increases

How does a straw work?

Review

1. Order from lowest to highest pressure. A<B<C C<B<A all are equal A

2. Look at the markers. Order from lowest to highest pressure. X A. Y<Z<X B. Y<X<Z C. Z<X<Y D. X<Z<Y E. two are equal Y E Z

3. What will happen to the pressure if more water is added? increase decrease stay the same A

increase decrease stay the same 4. What will happen to the pressure if more water is added while the same amount is removed? increase decrease stay the same C

increase decrease stay the same 5. What will happen to the pressure if the fluid were changed to honey? increase decrease stay the same A

increase decrease stay the same 6. If the 250 kg mass was put on the water column, what will happen to the pressure? A increase decrease stay the same

increase by 101.3 kPa decrease by 101.3 kPa stay the same 7. If the only change was to remove the air pressure , what will happen to the pressure? increase by 101.3 kPa decrease by 101.3 kPa stay the same Something else B

8. If the only change was to go to a place where the gravity was doubled, what will happen to the pressure? Both pressures would double Only the air pressure would double The air pressure would double, and the water pressure would increase some Something else A

9. How do the pressures at the two locations compare? X Y 9. How do the pressures at the two locations compare? C X>Y Y>X They are the same

Review What is the relationship between the depth of water and the pressure it exerts? How is pressure distributed at a given level in a fluid? How does the pressure exerted by the atmosphere change as altitude increases? Why don’t you feel the pressure exerted by the atmosphere?

Review A 500 N student stands on one foot. A 750 N student stands on two feet. If both students wear the same size shoe, which exerts the greater pressure? A circus performer on a pair of stilts exerts a pressure of 32 kPa on the ground. If the performer stands on one stilt, what pressure does the stilt exert on the ground?

Forces and Pressure in Fluids Chapter 13 Section 2 Pg. 394-397

Transmitting Pressure in a Fluid Recall: A _____ exerts pressure equally in all directions at a given _____. The amount of pressure exerted by a fluid depends on the ____ of fluid and its depth.

Pascal’s Principle Note that the pressure increases _______ throughout the water, not just at the _____ where you squeeze- discovered by Pascal in 1600s. According to _______ principle, a change in pressure at any point in a fluid is transmitted equally and ___________ in all directions throughout the fluid.

Hydraulic Systems A hydraulic system is a device that uses __________ fluid acting on pistons of different sizes to change a force. An ________ output force is produced because a _______ fluid pressure is exerted on the ______ area of the output piston.

Hydraulic Systems In the picture, an _____ force is applied to the small piston, which pushes against the fluid sealed in the _________________. Due to Pascal’s principle, we know that the pressure produced by the small piston is ________ through the fluid to the large piston. The pressure on both pistons is the ____. However, the pressure pushing against the large piston acts on a much larger ____, which is the key to how the system works. The large _____ force is used to lift and dump the load. The amount the input force is increased depends on the _____ of the pistons. If the large piston has 8 times the area of the _____ piston, then the output force is 8 times greater than the input force

Bernoulli’s Principle Get out a piece of paper Daniel Bernoulli- _____ scientist ________: as the speed of a fluid increases, the pressure within the fluid _________ As the air blows _____ the top of the paper, the pressure exerted by the air decreases. Because the air below the paper is nearly __________, it exerts a greater pressure. The difference in pressure forces the paper ________.

Bernoulli’s Principle Wings and Lift _________ principle help explain the flying ability of birds and airplanes. Air traveling over the ___ of an airplane wing moves faster than the air passing underneath, creating a ___________ area above the wing. The pressure difference between the top and the bottom of the wing creates an upward force known as a _____ Wings of birds produce a similar lift to airplanes, but birds can flap their wings to produce _______ movement and some lift Wings can also be used to create a downward force: race cars often have a ______ (upside-down wing) to give better traction

Bernoulli’s Principle Spray Bottles Think of a hose-end sprayer. (Often used to apply fertilizers) A _________ solution of a chemical is placed in the solution chamber and the sprayer is then attached to a hose. As water streams through the sprayer, it passes over the ___of a small tube that reaches down into the solution chamber. The fast-moving water creates a _______ area at the top of the tube which forces the solution up the tube where it then _____ with the water and is sprayed out of the end of the sprayer

Buoyancy Chapter 13 Section 3 Page 400-404

Buoyant Force _______ is the ability of a fluid to exert an upward force on an object placed in it Buoyancy results in the apparent loss of ______ of an object in a fluid. When an object is submerged in water, the water exerts an ______ force on the object, making it easier to lift. The upward force acts in the _______ direction of gravity and is referred to as buoyant force

Buoyant Force How it is produced… Since water pressure ________ with depth, the forces pushing up on the bottom of the object are greater than the _____ from pressure pushing _____ on the top of the object (any non-vertical forces cancel one another out), resulting in a net upward force- the buoyant force

Archimedes’ Principle Archimedes- an ancient _____ mathematician Archimedes’ Principle- the buoyant force on an object is equal to the weight of the fluid _________ by the object When an object is submerged, it _____ aside, or displaces, a volume of fluid _____ to its own volume. When an object _____ on the surface, it does not displace its entire volume. However, it does displace a volume equal to the ______ of the part of the object that is submerged

Density and Buoyancy Recall: ______ is the ratio of an object’s mass to its volume Density is often expressed in _____ of grams per cubic centimeter (g/cm3) Water has a density of 1 g/cm3 Steel has a density of 7.8 g/cm3 If an object is ____ dense than the fluid it is in, it will float. If the object is ____ dense than the fluid it is in, it will sink.

Density and Buoyancy The force of ______, equal to the object’s weight, acts ________ on the object. The buoyant force, equal to the weight of the volume of ______ fluid, acts upward on the object. When the buoyant force is _____ to the weight, an object floats or is suspended. When the buoyant force is ____ than the weight, the object sinks. (see pg. 401)

Density and Buoyancy Suspended Sinking When an object has the ____ density as the fluid it is submerged in. Buoyant force exactly ____ the object’s weight Neutral buoyancy Sinking When an object’s weight is _____ than the buoyant force acting on it ________ buoyancy

Density and Buoyancy Floating When the buoyant force is greater than the object’s weight _______ buoyancy Objects float more easily in _____ fluids Heavy ships can float because of the _____ of the hull. It displaces a large volume of water, creating a _____ buoyant force The ______ the fluid is, the greater is the weight displaced, which results in a greater buoyant force

Density and Buoyancy

Density and Buoyancy See page 402 in your book for how a submarine works.

Works Cited Frank, Wysession, & Yancopoulos. “Chapter 13 Forces in Fluids.” Physical Concepts in Action. Upper Saddle River: Pearson, 2010. 390-404. Print.