PROPERTIES OF MATTER 12.2

Chapter Twelve: Properties of Matter  12.1 Properties of Solids  12.2 Properties of Fluids  12.3 Buoyancy

Chapter 12.2 Learning Goals  Explain how pressure is created in fluids.  Discuss differences between the density of solids and fluids.  Apply Bernoulli’s principle to explain how energy is conserved in fluids.

12.2 Properties of Fluids  A fluid is defined as any matter that flows when force is applied.  Liquids like water or silver are kinds of fluid.

12.2 Pressure  A force applied to a fluid creates pressure.  Pressure acts in all directions, not just the direction of the applied force.

12.2 Forces in fluids  Forces in fluids are more complicated than forces in solids because fluids can change shape.

12.2 Units of pressure  The units of pressure are force divided by area.  One psi is one pound per square inch.

12.2 Units of pressure  The S.I. unit of force is the pascal.  One pascal (unit of force) is one newton of force per square meter of area (N/m 2 ).

12.2 Pressure  If your car tires are inflated to 35 pounds per square inch (35 psi), then a force of 35 pounds acts on every square inch of area inside the tire. What might happen if you over-inflate a tire?

12.2 Pressure  On the microscopic level, pressure comes from collisions between atoms.  Every surface can experience a force from the constant impact of trillions of atoms.  This force is what we measure as pressure.

12.2 Pressure  In a car engine high pressure is created by an exploding gasoline-air mixture.

12.2 Energy conservation and Bernoulli’s Principle  Streamlines are imaginary lines drawn to show the flow of fluid.  Bernoulli’s principle tells us that the energy of any sample of fluid moving along a streamline is constant.

12.2 Bernoulli’s Principle  Bernoulli’s principle says the three variables of height, pressure, and speed are related by energy conservation.

12.2 Three Variables and Bernoulli’s Principle  If one variable increases along a streamline, at least one of the other two must decrease.  For example, if speed goes up, pressure goes down.

12.2 The air foil  One of the most important applications of Bernoulli’s principle is the airfoil shape of wings on a plane.  When a plane is moving, the pressure on the top surface of the wings is lower than the pressure beneath the wings.  The difference in pressure is what creates the lift force that supports the plane in the air.

12.2 Hydraulics and Pascal’s Principle  Hydraulic lifts and other hydraulic devices use pressure to multiply forces and do work.  The word hydraulic refers to anything that is operated by a fluid under pressure.  Hydraulic devices operate on the basis of Pascal’s principle, named after Blaise Pascal.

12.2 Hydraulics and Pascal’s Principle  Pascal’s principle states that the pressure applied to an incompressible fluid in a closed container is transmitted equally in all parts of the fluid.  An incompressible fluid does not decrease in volume when pressure is increased.

12.2 Hydraulics and Pascal’s Principle  A small force exerted over a large distance is traded for a large force over a small distance.

12.2 Pressure  Pressure is force divided by area.

12.2 Force  You can calculate the force exerted if you know the pressure and area.

Solving Problems  On a hydraulic lift, 5 N of force is applied over an area of m 2.  What is the output force if the area of the larger cylinder is 5.0 m 2 ?

1.Looking for:  …output force 2.Given  …input force = 5 N; input area =.125 m 2 ; output area = 5 m 2 3.Relationships:  Pressure = ForceForce = P x A Area Solving Problems

4.Solution  Solve for pressure using input force.  Pressure = 5 N= 40 N/m 2.125m 2  Use Pascal’s law principle and use equivalent pressure to solve for output force.  Force = 40 N x 5 m 2 = m 2 Solving Problems 200 N

12.2 Viscosity  Viscosity is the property of fluids that causes friction.  Viscosity is determined in large part by the shape and size of the particles in a liquid.

12.2 Viscosity and temperature  As the temperature of a liquid increases, the viscosity of a liquid decreases.  Increasing the kinetic energy of the substance allows the particles to slide past one another more easily.

Investigation 12C  Key Question: What is the maximum load a boat can hold before sinking? How is the maximum load affected by the density of the water in which the boat floats? Density of Fluids