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Physical Science II. Fluid Physics. Fluids. Question : What are the three common states of matter?. Fluids. Three common states of matter: (1) Solid (2) Liquid (3) Gas
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Physical Science II Fluid Physics
Fluids • Question: • What are the three common states of matter?
Fluids • Three common states of matter: (1) Solid (2) Liquid (3) Gas • Thus far, we have focused primarily on solids. In this unit, we will be investigating the physics of liquids and gases…
Fluids • Fluid – a nonsolid state of matter in which the atoms or molecules are free to move past each other—includes both liquids and gases: • Solids have a definite volume and shape. • Liquids have a definite volume but not a definite shape—take the shape of the container they are placed in • Gases do not have a definite volume or shape—spread out when placed in a larger container
Pressure • Which is more comfortable to sit on? • A recliner or a bicycle seat • The recliner is obviously the more comfortable choice, but why? • The recliner is more comfortable because it reduces the pressure acting on your body.
Pressure • Pressure – the force per unit area acting on a surface: • In terms of the bicycle seat and the recliner, the recliner is more comfortable because it has a larger surface area. • The larger surface area causes the pressure to be lower.
Pressure • Pressure is measured in Pascals (Pa), where 1 Pa = 1 N/m2
Pressure • Question • What do you feel when you dive to the bottom of a deep pool?
Pressure • As you travel deeper in a fluid, the pressure increases. • The only two factors that determine pressure in a fluid are depth and the type of fluid. • For example: • If we climb to 3000 feet above sea level, we don’t notice the change in air pressure. • If you dive only 8 feet below the surface of water you notice a much larger pressure acting on your body.
Air Pressure • We live at the bottom of a vast quantity of air. • The Earth’s atmosphere, what we call air, is made up of many different types of gasses. • The air pressure at sea level is approximately 100,000 Pascals. • Just as pressure increases with depth under water, the same is true of air pressure.
Air Pressure • If you’ve ever felt your ears pop while driving up a mountain or flying in a plane you’ve experienced your bodies reaction to a change in air pressure. • You may be surprised to hear that right now there are 1000N of force pushing down on your head from the atmosphere. • The only reason you survive this pressure is because your body is exerting it’s own pressure against the atmosphere.
Air Pressure • Air pressure is measured with an instrument known as a barometer. • The barometer is a device commonly used by meteorologists to help determine the weather forecast. • A rising barometer usually indicates clear weather with low humidity. • A falling barometer indicates the approach of a storm system.
Pascal’s Principle • Pascal’s Principle –a pressure applied to a fluid in a closed container is transmitted equally to every point of the fluid and to the walls of the container: • Example 1 – When air is added to a tire, the pressure increases at all points inside the tire by the exact same amount.
Pascal’s Principle • Example 2 – In a hydraulic lift, when a small force F1 is applied to a small piston of area A1, a larger force F2 is transmitted to a larger piston of area A2: Thus, if A2is greater than A1, then F2is greater than F1!
Pascal’s Principle • Hydraulic lifts operate by utilizing Pascal’s Principle. • In an auto body shop, hydraulic lifts allow vehicles to be elevated in order to be inspected and repaired. • Large construction vehicles use hydraulics to operate shovels.
Pascal’s Principle • The advantage of hydraulics is the ability to move large forces by only exerting a small force. • This is exactly like the operation of a simple machine. • Like a simple machine, if you increase your output force, you will also decrease the output distance.
Buoyancy • Have you ever stood in a pool and tried lifting a friend while submerged in the water? • If you have, you probably noticed how easy it was to lift your friend. • So, why is lifting your friend easier in the pool?
Buoyancy • Buoyant Force – an upward force that acts on an object in a fluid. • Every object in a fluid experiences a buoyant force. • When you and your friend are in a pool, the buoyant force from the pool water acts against the gravitational force on your bodies, • This makes it seem as if you and your friend weigh less.
Buoyancy • Apparent Weight – in a fluid your apparent weight is equal to your actual weight minus the buoyant force. • There are several methods to find the buoyant force acting on an object, but the most important came from a Greek mathematician named Archimedes.
Archimedes’ Principle • Archimedes discovered an important property of buoyancy. • If you make the mistake of filling a bathtub too high, the water is going to overflow when you get into the tub. • The reason for this is because water is displaced to make room for your body to fit in the tub.
Archimedes’ Principle • Archimedes’ Principle – the buoyant force on an object is equal to the weight of the fluid that is displaced by that object. • To measure the buoyant force you can collect the water that is displaced by an object and measure the weight of that water. • The weight of the water is equal to the buoyant force.
Density and Buoyancy • Whether or not an object will float is based on density. • If an object is more dense than the liquid it is placed in, it will sink. • If an object is less dense than the liquid it is placed in, it will float.
Density and Buoyancy • The buoyant force acting on a floating object is exactly equal to the weight of that object. • Floating objects have an apparent weight of zero Newtons. • Also, since the buoyant force is equal to the weight of water displaced, floating objects must displace an amount of water that weighs as much as the object.
Density and Buoyancy • Examples: • When a 1500 N boat is floating in water, it is displacing 1500 N of that water. • If a 500 N person is floating in a pool, they are displacing 500 N of water.
Principles of Flight • In some of the earliest records of human history, studies of flight have been discovered. • The ancient Greeks studied birds in great detail and the Italian inventor Leonardo Da Vinci designed several flying machines. • For centuries humans had been attempting to fly with all sorts of wild creations, but it was the Wright brothers who eventually succeeded in controlled flight.
Principles of Flight • Since the Wright brothers’ historic flight there have been many advancements in the design of aircraft. • However, all flight is based on a series of physics principles.
Principles of Flight • Flight is possible because it occurs within the atmosphere of the Earth. • Earth’s atmosphere is a fluid that is made up of several different types of gasses most notably, nitrogen, oxygen and carbon dioxide. • The ability to fly through this fluid is based on four forces: • Lift, Thrust, Drag and Weight
Lift • One of the most important aspects of flight is lift. • Lift – the upward force acting on an airplane. • The cause of lift is a difference in air pressure on the top and bottom of the wing, which is explained by Bernoulli’s Principle. • Bernoulli’s Principle explains that when the speed of a fluid increases, the pressure within the fluid decreases.
Lift • The wing of an airplane is shaped so that the air moving over the top of the wing travels faster than the air moving around the bottom of the wing. • A lower pressure is created on top of the wing by the faster moving air. • The higher air pressure on the bottom of the wing provides the upward force that lifts the airplane.
Thrust • While lift allows the airplane to get off the ground, it would not exist without any thrust. • In order for lift to be generated, the air must be moving around the wing at a high velocity. • The engines of the airplane provide the force that pushes it to speeds that are great enough to generate the lift.
Thrust • Thrust is the force that is provided by the engines to move the airplane. • In order for the plane to get off the ground, the engines must provide enough thrust to move the air around the wings with enough speed to generate lift. • As long as the thrust is strong enough, the airplane will experience lift.
Drag • It is important to remember that air is made up of many different molecules and therefore it creates friction. • Air resistance is the friction that is created by the Earth’s atmosphere. • In terms of flight, air resistance produces an effect called drag. • Drag is simply the force of the air resistance that is acting against the forward motion of an airplane.
Drag • The drag forces that act against the motion of an airplane reduce fuel efficiency. • The more drag there is, the less efficient the aircraft.
Weight • The last of the forces involved in flying is weight. • Remember that weight is the force of gravity that is acting on an object. • In order for an airplane to get off the ground and to stay in flight, the lifting force must overcome the weight of the plane.
Forces of Flight • All in all, the success of flight is dependent on all four forces acting together. • If thrust and drag are equal, the plane will move at a constant speed. • If weight and lift are equal, the plane will fly at a constant altitude.