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Force In Fluids Chapter 11. Section 1: What is Pressure?. What is Pressure?. Defined as force exerted on a surface Earth’s gravity pulls downward Due to gravity, your feet exert a force on the surface of Earth over an area the size of your feet. Pressure vs. Area.
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Section 1:What is Pressure? What is Pressure? • Defined as force exerted on a surface • Earth’s gravity pulls downward • Due to gravity, your feet exert a force on the surface of Earth over an area the size of your feet
Pressure vs. Area • The amount of pressure you exert depends on the area over which you exert force. • Larger area = less pressure exerted • Where could you actually see this pressure exerted?
Pressure vs. Area What is Pressure? • Formula a. Pressure = Force Area • SI Units; Pascals (Pa) = 1 N/m² • What kind of relationship do pressure and area have?
What is fluid pressure? Fluid Pressure • Fluid Pressure • 1. Fluid is a material that can easily flow. Examples: • 1. Liquids • 2. Gases • Air and helium • 2. Fluids can change shape
What is fluid pressure? What Causes Fluid Pressure • What causes fluid pressure? • In a fluid, all of the forces exerted by the individual particles combine to make up the pressure exerted by the fluid.
What is Air Pressure? Air Pressure • Air Pressure • Air exerts pressure because it has mass • Because the force of gravity pulls down on the mass of air, the air has weight • Weight of the air is the force that produces air pressure or atmospheric pressure
What is Balanced Pressure? Balanced Pressure 9. Balanced Pressure 1. Pressure exert is equal on all sides. 2. It explains why you aren’t crushed from air pressure. Let’s try! Hold out your hand • Holding up air – 1,000 N • About the same weight as that of a large washing machine
Example • Heat and can demo • Explain what happened to the can.
Variations in Fluid Pressure Variations in Fluid Pressure • Atmospheric Pressure and Elevation • a. Atmospheric pressure ____________as your elevation increases • Popping in ear is caused by changing air pressure. • Higher elevations – less air above you = less air pressure
Variations in Fluid Pressure Variations in Fluid Pressure • 10. Variation in Fluid Pressure • 2. Water Pressure and Depth • 1. Water pressure increases as depth ____________ • 2. Deepest part of the ocean 1,000 times greater air pressure than we experience every day
How is Pressure Measured? Measuring Pressure • Measuring Pressure 1. Barometer measures atmospheric pressure
Weather Changes • Barometers can signal a change in weather is going to occur • Rapidly decreasing pressure usually signals a storm is coming
Section 2:Floating and Sinking Which will float?
Why is the ship able to float? • It has a larger surface area to spread out it’s weight • To float the buoyant force must equal the weight of the ship
Buoyancy Buoyancy • Defined asthe ability to float.
Buoyant Force Buoyant Force • Buoyant force is when water and other fluids exert an upward force. • The buoyant force acts in the direction opposite to the force of gravity, so it makes an object feel lighter. • The less dense the object is, the greater the buoyant force it experiences.
Who is ? 6. Archimedes’ Principle • Lived: 287 - 212 BC • Greek mathematician, physicist, engineer, inventor, and astronomer. • Invented: Pulley Systems, War Machines, • Developed a way to find the volume of an’ • irregular object • Education: Studied in Alexandria, Egypt
B. Floating and Sinking Who is ? 6. Archimedes’ Principle • Archimedes Principle states: An object that is submerged in a liquid will experience an additional upward force (due to the submersion) that is equal to the weight of the amount of liquid that was displaced by the object. This force is called the “buoyant force”.
Density Density • Density • Mass per unit volume for a object • Formula = Mass/Volume • SI units = g/cm3 • Density of water = 1.0 g/cm3 • Density of ice = .94 g/cm3
Density • Comparing densities, you can predict whether an object will float or sink in a fluid. • If object is ____________than fluid – it sinks • If object is _____________ than fluid - it floats • An object with a density equal to that of the fluid floats at a constant depth.
Changing density can explain why an object floats or sinks Changing Density • If you change the density of an object you can make it sink or float • How can you change the density of the following items? • Submarine • Water • balloon
How does a submarine work? • What happens for it to dive? • What happens for it to surface?
Changing Water’s Density Changing water’s density • What could you do to water to make it less dense?
Why do Balloons Float? Why do balloons float? • What are balloons filled with when they float in the air? Why do they float? • What would happen if you filled a balloon with something more dense than air? https://www.youtube.com/watch?v=u19QfJWI1oQ
Section 3: Pascal’s Principle • Transmitting Pressure in a fluid • In the 1600s, Blaise Pascal developed a principle to explain how pressure is transmitted in a fluid b. Fluid exerts pressure on any surface it touches.
Pascal’s Principle Pascal’s Principle • Pascal’s Principle 1. Pascal’s principle states that pressure increases by the same amount throughout an enclosed or confined fluid 2. *When force is applied to a confined fluid, the change in pressure is transmitted equally to all parts of the fluid.*
Pascal’s Principle at Work Why does water come out of a water bottle?
Pascal’s Principle Hydraulic Systems • Hydraulic System’s and Pascal’s Principle 1. Hydraulic system uses liquids to transmit pressure and multiply force in a confined fluid. https://www.youtube.com/watch?v=tzqP7VKF9GE
C. Pascal’s Principle Hydraulic Systems • Hydraulic System’s and Pascal’s Principle 2. A hydraulic system multiplies force by applying the force to a small surface area. The increase in pressure is then transmitted to another part of the confined fluid, which pushes on a larger surface area. a. Because hydraulic systems use fluids to transmit pressure, hydraulic systems have few moving parts that can jam, break or wear down.
Example Problem • 10 N of force is applied to a 10cm2 piston that transmits pressure to a 2nd piston (200cm2). How much is the force multiplied from traveling through the pistons?
Section 4:Bernoulli’s Principle Bernoulli’s Principle: • Daniel Bernoulli • A Swiss scientist born in 1700’s that is most famous for his work in fluid pressure. • He found that the faster the fluid moves the less pressure the fluid exerts.
Fluid motion • Fluids naturally move from an area of _______ pressure to an area of ______ pressure.
How does this relate to drinking out of a straw? Bernoulli’s Principle: • Higher air pressure pushing down on the surface of the drink forces fluid up straw where there is less pressure.
Bernoulli’s Principle Bernoulli’s Principle: • 3. Bernoulli's principle: • States that as the speed of a fluid increases, its pressure decreases • The faster a fluid moves, the less pressure the fluid exerts
D. Bernoulli’s Principle • Bernoulli’s principle explains flight from a small kite to a huge airplane. • Objects are designed so that their shapes cause air to move at different speeds above and below them. • If the air moves faster above the object, pressure pushes the object upward. • But if air moves faster below the object, pressure pushes it downward.
D. Bernoulli’s Principle Curve Ball C. Bernoulli’s Principle View airplane wings explanation.
