Transcript Slide 1
Section 13.1 Fluid Pressure Pressure is defined as the result of a force distributed over an area. There are several units that are used to express pressure: kPa = kilopascal atm = atmospheres psi = pounds per square inch mm Hg = millimeters of mercury 101.3 kPa = 1atm = 14.7 psi = 760mm Hg Fluid Pressure Calculating Pressure When we calculate pressure, we must know the: Amount of force (in newtons N) The area covered by the force Formula for calculating pressure Pressure = Force/Area or P = F/A * Remember: Force = Weight = Newtons Fluid Pressure Problem A block of steel with a weight of 100 newtons rests on a table with an area of 2 square meters what pressure does the steel exert on the desk? Fluid Pressure Answer: Pressure P = mass/area or P = M/A =? M = 100 N A = 2 m2 P = 100N / 2m P = 50 N/m2 or 50 Pa or .05 kPa. Fluid Pressure Pressure in Fluids. Both liquids and gases are fluids. Gases are more compressible than liquids because they have a greater distance between particles. The pressure in a fluid (gas or liquid) at any given depth is constant and exerted equally in all directions. For a fluid at rest, the two factors that determine pressure are depth and type of fluid. Notice the different shapes the fluid assumes in this Pascal Vase. How will this affect the pressure at any given point in the liquid? Fluid Pressure Air Pressure and the atmosphere. Air pressure decreases as altitude increases. Air pressure at Myrtle Beach (sea level) is greater than air pressure at Mount Mitchell. The column of air over you at Myrtle beach is taller than the column of air over you on top of Mount Mitchell This is a function of depth in a gas. Section 13.1 Quiz 1. The result of a force being distributed over an area is ______. 2. Water pressure increases as ______ increases. 3. ______ and _______ are both states of matter that are fluids. 4. The two things that affect pressure in a fluid are ______ and ______. 5. What is the formula for pressure? Fluid Pressure Section 13.2, Forces & Pressures in Fluids Transmitting Pascal’s Pressure in a Fluid Principle – A change in pressure in a fluid at any point is transmitted equally and unchanged in all directions throughout the fluid. Section 13.2, Forces & Pressures in Fluids Hydraulic Systems Hydraulic systems are devices that use pressurized fluid acting on pistons of different sizes to change a force. In a hydraulic lift system, an increased output force is produced because a constant fluid pressure is exerted on the larger area of the output piston. The larger area of the output piston can produce a strong enough force to lift a heavy load due to equal distribution of force throughout the system. Section 13.2, Forces & Pressures in Fluids Bernoulli’s Principle Bernoulli’s principle states that as the Speed of a fluid increases, the pressure within the fluid decreases. Section 13.2, Forces & Pressures in Fluids Bernoulli’s Principle Wings and Lift On an airplane in flight, the air moving across the top of the wing is moving faster than the air moving underneath it. The fast moving air creates a low pressure area above the wing, while the slower moving air underneath the wing creates a high pressure area. The result is the upward lifting of the wing/airplane. Section 13.2, Forces & Pressures in Fluids Spray Bottles When a garden hose is attached to a spray bottle, the water from the hose runs through a pipe with another pipe leading into the fertilizer solution in the bottom of the spray bottle. The fast moving water from the garden hose creates a low pressure area and the fertilizer solution is pulled up into the pipe. See next page. Section 13.2, Forces & Pressures in Fluids Section 13.2 Quiz “A change in pressure at any point in a fluid is transmitted equally and unchanged in all directions throughout the fluid.” This is known as ________ ________. 2. According to Bernoulli’s principle, as the speed of a fluid increases, the pressure within the fluid ________. 1. Section 13.2 Quiz 3. The faster moving air over the top of an airplane wing creates an area of _______ pressure, while the slower moving air creates an area of _______ pressure. 4. Fluids flow from areas of ______ pressure to areas of ______ pressure. 5. A block of iron resting on a table with a surface area of 3 square meters exerts a force of 1200 Newtons. What is the pressure on the table top? Section 13.3, Buoyancy Section 13.3, Buoyancy Section 13.3, Buoyancy Section 13.3, Buoyancy Buoyant Force Buoyancy is the ability of a fluid to exert an upward force on an object placed in it. Buoyant force acts opposite the force of gravity on an object. When an object becomes buoyant in a fluid, it experiences an apparent weight loss. Section 13.3, Buoyancy Archimedes Principle Archimedes Principle states that the buoyant force on an object is equal to the weight of the fluid displaced by the object. Section 13.3, Buoyancy Density and Buoyancy Density and buoyancy are very closely related. If an object is more dense than the fluid it is in, it will sink. If an object is less dense than the fluid it is in it will float. If an object is the same density as the fluid it is in, it will become suspended. Notice that the Goodyear Blimp and the British research ship Europa are both buoyant in the fluids they are moving in. Section 13.3, Buoyancy The density of a substance is calculated by dividing its volume into its mass, using the formula D = m/v. Problem: A sample of quartz has a mass of 42g, and it’s volume is 6cm3. What is its density? Section 13.3 Quiz 1. The ability of a fluid to exert an upward force on an object placed in it is called __________. 2. A buoyant force acts on an object in the ________ direction that the force of gravity does. 3. If an object is more dense than the fluid it is in, it will _________. Section 13.3 Quiz 4. If an object is the same density as the fluid it is in, it will ___________. 5. If an object is of a lower density than the fluid is in it will _______. 6. We calculate the density of a substance by dividing its _______ into its _______.