Chapter 1.2 Chapter 1.2 NotesNotes

PressurePressure

All matter is made up of All matter is made up of atomsatoms and and moleculesmolecules..

Matter can exist in four Matter can exist in four states:states:Liquid, Solid, Gas, Liquid, Solid, Gas, and Plasmaand Plasma

In a In a SolidSolid, molecules , molecules are constantly are constantly moving, but they do moving, but they do no move around in the no move around in the solid but instead solid but instead vibrate in a fixed vibrate in a fixed location.location.

In a In a LiquidLiquid, molecules are , molecules are no longer confined to a no longer confined to a fixed position. Molecules fixed position. Molecules vibrate, but can now easily vibrate, but can now easily slide over one another and slide over one another and move about – it takes the move about – it takes the shape of its shape of its ContainerContainer. .

In a In a GasGas, molecules , molecules move freely about the move freely about the container. When they container. When they hit each other or the hit each other or the container they bounce container they bounce around like billiard around like billiard balls. The shape of a balls. The shape of a gas takes the shape gas takes the shape of the of the containercontainer. .

In temperatures above In temperatures above 2000 degrees Celsius, 2000 degrees Celsius, electrons separate from electrons separate from atoms to form ions. A atoms to form ions. A gas containing free gas containing free electrons and ions is electrons and ions is called called PlasmaPlasma..

Both liquids and gases Both liquids and gases are are fluidsfluids. A fluid is a . A fluid is a material that can flow, material that can flow, has no has no definitedefinite shape shape of its own, and of its own, and conforms to the shape conforms to the shape of its container.of its container.

A A hydraulichydraulic system system uses a liquid as a uses a liquid as a fluid, which is called fluid, which is called a working fluid.a working fluid.

Hydraulic Robot Hydraulic Robot DemoDemo

A A pneumaticpneumatic system uses system uses a gas as its working fluid.a gas as its working fluid.

The The densitydensity of a material of a material is the amount of matter per is the amount of matter per unit volume.unit volume.

Density = Density = mass / volumemass / volume SI Units of density is SI Units of density is kg/mkg/m33

Coke versus Diet CokeCoke versus Diet Coke

Density is sometimes written Density is sometimes written as a comparison of an as a comparison of an object’s weight to its volume. object’s weight to its volume. This is called This is called weight weight densitydensity..

Weight density = Weight density = weight / volumeweight / volume

SI units of weight density are SI units of weight density are N/mN/m33

A volume of 500 cm3 of a A volume of 500 cm3 of a fluid has a mass of 550 g. fluid has a mass of 550 g. What is the density? What is the density?

• Density = mass/volumeDensity = mass/volume• Density = 550kg / 500cmDensity = 550kg / 500cm33

• Density = 1.1 kg/cmDensity = 1.1 kg/cm33

A force applied over a A force applied over a surface is surface is pressurepressure..

Pressure = Pressure = force / areaforce / area

SI units of pressure SI units of pressure are are N/mN/m22 or Pascal or Pascal

Pressure Pressure DemosDemos

Bed of NailsBed of NailsBottomless Bottomless BottleBottle

A block has an area of .01 mA block has an area of .01 m22 and exerts a force of 50 N on a and exerts a force of 50 N on a table. Calculate the pressure table. Calculate the pressure the block exerts.the block exerts.

• Pressure = Force / AreaPressure = Force / Area• Pressure = 50 N / .01 mPressure = 50 N / .01 m22

• Pressure = 5000 NmPressure = 5000 Nm22 or or PascalsPascals

The pressure increases The pressure increases as the as the depthdepth increases.increases.

Pressure = weight Pressure = weight density x density x fluid depthfluid depth

The height of a fluid in a storage The height of a fluid in a storage tank is 100 cm above a valve. tank is 100 cm above a valve. Find the pressure at the valve if Find the pressure at the valve if the weight density is 13.6 g / the weight density is 13.6 g / cmcm33..

1.1. Pressure = weight density x Pressure = weight density x depthdepth

2.2. Pressure = 13.6 g/cmPressure = 13.6 g/cm33 x 100 cm x 100 cm3.3. Pressure = 1360 g/cmPressure = 1360 g/cm22

Water exerts an Water exerts an upward force on all upward force on all objects. This upward objects. This upward force is called the force is called the buoyant forcebuoyant force and is and is caused by the caused by the pressurepressure increasing increasing with depth.with depth.

Page 35, draw in figure 1.20Page 35, draw in figure 1.20

If buoyant = weight density x Volume If buoyant = weight density x Volume = = weight of water displacedweight of water displaced

If the weight of the brick is greater If the weight of the brick is greater than the buoyant force, the brick will than the buoyant force, the brick will sink.sink.

If the weight of the brick is less than If the weight of the brick is less than the buoyant force, the brick will the buoyant force, the brick will float.float.

If the weight of the brick is equal to If the weight of the brick is equal to the buoyant force, the brick will the buoyant force, the brick will stay stay in the same place.in the same place.

Archimede’s Archimede’s PrinciplePrinciple states that states that an object immersed in an object immersed in a fluid has an upward a fluid has an upward force exerted on it force exerted on it equal to the weight of equal to the weight of the fluid displaced by the fluid displaced by the object.the object.

Two simple density rules of Two simple density rules of whether an object will float:whether an object will float:

1.1. If the object has a greater If the object has a greater density than the fluid, it density than the fluid, it will will Sink.Sink.

2.2. If the object has a lower If the object has a lower density than the fluid, it density than the fluid, it will will Float.Float.

Use table 1.4 on page 30 Use table 1.4 on page 30 to answer this question: to answer this question:

Will a block of lead float Will a block of lead float or sink in mercury?or sink in mercury?

Lead has a density of Lead has a density of 11.3 and Mercury 13.6 - 11.3 and Mercury 13.6 - FloatFloat

Pascal’s PrinciplePascal’s Principle says a says a change in pressure at any change in pressure at any point in a confined fluid is point in a confined fluid is transmitted undiminished transmitted undiminished throughout the fluid.throughout the fluid.

P1 = P2; Since pressure = F/A; P1 = P2; Since pressure = F/A; F1/A1 = F1/A1 = F2/A2F2/A2

Suppose F1 = 10N, what is the F2 Suppose F1 = 10N, what is the F2 if A1=.1 mif A1=.1 m22 and A2 = 2 m and A2 = 2 m22??

F1/A1 = F2/A2F1/A1 = F2/A2 10/.1 = F2 / 210/.1 = F2 / 2 100 = F2 / 2100 = F2 / 2 2 x 100 = F22 x 100 = F2 200 N = F2200 N = F2

On earth, we live at the bottom On earth, we live at the bottom of a thick blanket of of a thick blanket of airair..

Air also has Air also has pressurepressure.. Air pressureAir pressure is caused by the is caused by the

weight of air above an area.weight of air above an area. Atmospheric pressure Atmospheric pressure

decreasesdecreases with altitude. with altitude. A A barometerbarometer is an instrument is an instrument

used for measuring atmospheric used for measuring atmospheric pressure.pressure.

Atmospheric Pressure DemoAtmospheric Pressure DemoEquilibriumEquilibrium

At sea level, the average atmospheric At sea level, the average atmospheric pressure is pressure is 101.3101.3. This equals a height . This equals a height of of 760 mm760 mm of mercury, and this pressure of mercury, and this pressure is called is called one atmosphereone atmosphere..

Absolute PressureAbsolute Pressure is the total pressure is the total pressure measured above zero pressure (a perfect measured above zero pressure (a perfect vacuum).vacuum).

Gage PressureGage Pressure is the pressure is the pressure measured above atmospheric pressure. measured above atmospheric pressure. Gage pressure is a measure of how much Gage pressure is a measure of how much greater the air pressure is inside the tire greater the air pressure is inside the tire than the than the air pressureair pressure outside the tire. outside the tire.

Absolute pressure = Absolute pressure = gage pressuregage pressure + + atmospheric pressureatmospheric pressure

The gage pressure is 33 psi and the The gage pressure is 33 psi and the atmospheric pressure is 14.7 psi, how atmospheric pressure is 14.7 psi, how much is the absolute pressure? much is the absolute pressure?

Absolute pressure = gage + atmosphericAbsolute pressure = gage + atmospheric

Absolute = 33 + Absolute = 33 + 14.714.7

Absolute = 47.7Absolute = 47.7

Fluid systems have 2 things in Fluid systems have 2 things in common. First they both contain a common. First they both contain a fluidfluid. Second, they have a pressure . Second, they have a pressure difference in the system that creates a difference in the system that creates a forceforce. Pressure is a . Pressure is a prime moverprime mover in in fluid systems.fluid systems.

If there is no pressure difference in a If there is no pressure difference in a system, there is no system, there is no movementmovement..

If a pressure difference exists, the fluid If a pressure difference exists, the fluid will flow until it creates will flow until it creates equilibriumequilibrium..

In equilibrium, h2 must equal In equilibrium, h2 must equal h1h1 and and P2 must equal P2 must equal P1P1..