Properties of Fluids SPH4C

Fluids Liquids and gases are both fluids: a fluid is any substance that flows and takes the shape of its container.

Fluids Liquids and gases are both fluids: a fluid is any substance that flows and takes the shape of its container. If the fluids are at rest, the study of them is called. If the fluids are in motion, the study of them is called.

Fluids Liquids and gases are both fluids: a fluid is any substance that flows and takes the shape of its container. If the fluids are at rest, the study of them is called fluid statics. If the fluids are in motion, the study of them is called.

Fluids The science and technology of the mechanical properties of liquids is called. Similarly, the science and technology of the mechanical properties of air and other gases is called.

Fluids The science and technology of the mechanical properties of liquids is called hydraulics. Similarly, the science and technology of the mechanical properties of air and other gases is called.

Fluids The science and technology of the mechanical properties of liquids is called hydraulics. Similarly, the science and technology of the mechanical properties of air and other gases is called pneumatics.

Systems The study of hydraulics and pneumatics includes the study of fluids that are not enclosed, such as lakes and air in the atmosphere, as well as pressurized systems that are enclosed.

Systems A hydraulic system is a mechanical system that operates using a liquid under pressure A pneumatic system operates using a gas under pressure.

What s the difference? Liquids flow and take the shape of their container but maintain a constant volume.

What s the difference? Gases expand to fill the available volume.

States of Matter Revisited This is because the difference in what the particles are doing.

Particle Theory Revisited 1. All matter is made up of extremely tiny particles. 2. Each pure substance has its own kind of particles, different from the particles of other pure substances. The same pure substance in three different states.

Particle Theory Revisited 3. Particles are always moving. Particles at a higher temperature are generally moving faster on average than particles at a lower temperature.

Particle Theory Revisited 4. Particles attract each other. See? They re smiling.

Solids In a solid, the particles are moving slowly enough that this attraction keeps them in a rigid structure.

Liquids In a liquid, the particles move fast enough that they can t stay in a rigid structure but they still want to stay close by.

Gases In a gas, however, the particles are moving even faster and fly by each other, bouncing off the edges of the container. Evaporation: a liquid molecule becoming a gas molecule.

Plasma Note that there is a 4 th state of matter called plasma which has free electrons that can conduct electricity and be influenced by magnetic fields. It is similar to a gas in its properties.

Compressibility Gases are therefore highly compressible: their particles can be forced back closer together.

Density This means that their density, their mass per unit volume, is variable. m m D m D V V V D

Density This means that their density, their mass per unit volume, is variable. m m D m D V V V D Density has units of kg/m 3.

Density: Example A quantity of helium gas at 0 C with a volume of 4.00 m 3 has a mass of 0.712 kg at standard atmospheric pressure. Determine the density of this sample of helium gas.

Density: Example A quantity of helium gas at 0 C with a volume of 4.00 m 3 has a mass of 0.712 kg at standard atmospheric pressure. Determine the density of this sample of helium gas. V m D 4.00m 3 0.712kg?

More About Density Density is a characteristic property of a substance: any sample of a pure substance at the same temperature and pressure has the same density.

The Properties of Fluids: More Practice

Pressure: Student Success Criteria I can solve problems and conduct an investigation related to the relationships between force, area, pressure, and volume.

An Introduction to Pressure SPH4C

Pressure Pressure is defined as the magnitude of the force per unit area: p F A

Pressure Pressure is defined as the magnitude of the force per unit area: p F A Pressure therefore has units of N/m 2

Pressure Pressure is defined as the magnitude of the force per unit area: p F A Pressure therefore has units of N/m 2, or pascals (Pa).

1 pascal 1 Pa is approximately equal to the pressure exerted by a single sheet of newspaper spread out on the floor.

1 pascal 1 Pa is approximately equal to the pressure exerted by a single sheet of newspaper spread out on the floor. Most pressures are therefore given in kilopascals (kpa): 1 Pa = 0.001 kpa

Example A crate is 2.0 m long and 1.0 m wide. The weight of the crate is 5.2 x 10 3 N. What pressure does the crate exert on the floor?

Example A crate is 2.0 m long and 1.0 m wide. The weight of the crate is 5.2 x 10 3 N. What pressure does the crate exert on the floor? A l w 2.0 m1.0 m 2.0 m 2 F 5.210 3 N p F A 5.210 2.0 m 3 2 N 2.610 3 Pa or2.6 kpa

Atmospheric pressure The weight of the layers of air above us exerts a pressure.

Atmospheric pressure Standard atmospheric pressure at sea level is 101.3 kpa (or 1 atmosphere). This instrument used to measure air pressure is called a barometer.

Atmospheric pressure A drinking straw works by decreasing the air pressure inside the straw: the atmospheric pressure is then greater than that in the straw and forces the liquid to rise up in the straw.

Atmospheric pressure Atmospheric pressure decreases at higher altitudes as there is less air above you.

Atmospheric pressure Atmospheric pressure decreases at higher altitudes as there is less air above you. This can cause your ears to pop when the pressure inside your ears is greater than the pressure outside.

Water Pressure Similarly pressure will increase with increasing depth under water as you have more water above you.

Measuring Pressure: Student Success Criteria I can conduct an investigation to identify factors that affect the static pressure head in fluids, compare theoretical and empirical values, and account for discrepancies.

Measuring Pressure SPH4C

Static Pressure Head For any point in a static fluid, the height of the column above that point is called the static pressure head. A dam must be thicker or stronger at greater depths to withstand the increased pressure.

Static Pressure Head The formula for the pressure exerted is: p F A mg A DV g D Ah A A g Dhg Where D is the density of the fluid, h is the height, and g = 9.8 m/s 2.

Barometers In mercury barometers, it is the static pressure head that indicates the external air pressure. The higher the atmospheric pressure, the higher the static pressure head.

Barometers In mercury barometers, it is the static pressure head that indicates the external air pressure. The higher the atmospheric pressure, the higher the static pressure head. Question: Why do we use mercury in barometers instead of water?

Water Level Liquid in connected containers exposed to the same air pressure will be at the same height. The shape and orientation of the containers makes no difference to the height.

Siphons This is often phrased as water seeks its own level, and is why water will even flow uphill in a siphon if it can reach a lower point at the end of the siphon. Note that the siphon needs to be full of liquid to connect the two containers.

Manometers Manometers can be used to measure variations in pressure. When more pressure is applied to the left side of the tube, there will be a difference in the heights of the liquid.

Gauge pressure This variation in pressure from atmospheric pressure is called the gauge pressure: gauge pressure absolute pressure atmospheric pressure p g p abs p atm Tire pressure gauges measure gauge pressure: the pressure over and above atmospheric pressure.

Gauge pressure example Pressure is applied to one end of a water manometer so that the difference between the two heights is 10 cm. (a) What is the gauge pressure applied? (b) What is the absolute pressure applied?

Gauge pressure example (a) What is the gauge pressure applied? D 1000 h 0.10 m g 9.8 m 2 s kg m 3

Gauge pressure example (a) What is the gauge pressure applied? D 1000 h 0.10 m g 9.8 m 2 s kg m 3 p Dhg kg m ( 1000 )(0.10m)(9.8 2 ) m 3 s 980 Pa or 0.980kPa

Gauge pressure example (b) What is the absolute pressure applied? p abs p g p atm 0.980kPa 101.3kPa 102.28kPa

Measuring Pressure: More Practice

Pascal s Principle: Student Success Criteria I can state Pascal's principle, explain its applications in the transmission of forces in fluid systems, and conduct an laboratory investigation to demonstrate it.

SPH4C

Compressibility Recall that liquids are not very compressible: their volume remains more or less constant even if pressure is applied.

Pascal s Principle Therefore, pressure applied to an enclosed liquid is transmitted to every part of the liquid and to the walls of the container. A hydraulic braking system transfers pressure from the brake lever through the system.

The hydraulic press Pascal used this principle in the design of a device called the hydraulic press: a device in which a small force on a small piston is transmitted through an enclosed liquid and applies a large force on a large piston.

The hydraulic press I.e., the pressure (p S ) on the small piston equals the pressure (p L ) on the large piston: p s p L F A s s F A L L If A is increased, then F is also increased.

The hydraulic press: Example A force of 14 N is applied to a piston of area 0.01 m 2, which is connected to another piston of area 0.25 m 2. What is the force on the larger piston?

The hydraulic press: Example A force of 14 N is applied to a piston of area 0.01 m 2, which is connected to another piston of area 0.25 m 2. What is the force on the larger piston? F A A F s s L L 14 N 0.01m 2 0.25m? 2

. Mechanical advantage The Ideal Mechanical Advantage (IMA) of the system would be: & Actual Mechanical Advantage (AMA) of the system would be

. Mechanical advantage The Ideal Mechanical Advantage (IMA) of the system would be: IMA & Actual Mechanical Advantage (AMA) of the system would be A A L s

. Mechanical advantage The Ideal Mechanical Advantage (IMA) of the system would be: IMA & Actual Mechanical Advantage (AMA) of the system would be A A L s AMA F F load effort F F L s

Distance However, since the volume of the larger cylinder is obviously larger, the distance the larger cylinder is displaced is smaller.

Brakes Car brakes incorporate both levers and hydraulics: the distance from the pedal to the pivot is four times the distance from the cylinder to the pivot, so the force at the pedal will be increased by a factor of four before it is transmitted to the cylinder. (2 nd class lever).

Brakes The diameter of the brake cylinder is three times the diameter of the pedal cylinder, increasing the area and therefore the force by a factor of nine. All together, this system increases the force of your foot by a factor of 36 (4 x 9 = 36).

Brakes So if you put 100 N of force on the pedal, 3600 N will be generated at the wheel squeezing the brake pads