This presentation is the property of its rightful owner.
1 / 38

Physical Science II PowerPoint PPT Presentation

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

Physical Science II

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

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

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.

Flight

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.