# ATAT101 Theory of Flight > # [[T101 Intro| ◀️ ]] &nbsp;[[T101 Home| Home ]] &nbsp;[[T101 Week 2| ▶️ ]] &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; [[QR T101 Week 1| 🌐 ]] ># [[T101 Week 1#ATAT101 Theory of Flight|Week 1]] >- [[T101 Week 1#The Nature of Flight|The Nature of Flight]] >- [[T101 Week 1#Composition of the Atmosphere|Composition of the Atmosphere]] >- [[T101 Week 1#Temperature|Temperature]] >- [[T101 Week 1#Pressure and Atmosphere|Pressure and Atmosphere]] >- [[T101 Week 1#Laws and Principles of Physics|Laws and Principles of Physics]] >[!jbplus|c-blue]- Lesson Intro >#### What > >In this lesson you will learn some fundamental concepts that underlie the science of flight. > >#### Why > >A technician must understand the physics and technology of how an aircraft works in order to understand how to maintain and repair it. > You will use this knowledge throughout your aviation career. > >#### Testing > >You will be tested on this material on Assignment 1, the Midterm, and the Final Test, as per the [[T101 Intro#Testing and Grades|testing strategy]]. > >#### Approach and Objectives > >By understanding the following topics, you will have achieved the learning outcome for this lesson. Consult your course outline for the learning outcomes and other details of this course. > >##### Course Learning Objectives CLO 3. Explain theory of flight applicable to fixed and rotary wing aircraft. ## The Nature of Flight %% Ref A, p.5-26,37; Ref C %% ![[T101_1_001.png|350]][[T101_1_001.png|➡]] ### Types of Flight [[V 101 The Nature of Flight|📺]] As you well know, flight is not a man-made phenomenon. The natural world has many examples of flight, including the flight of birds, both by flapping their wings, and by gliding with their wings outstretched. Smoke from fires will rise upward and take flight, and leaves blown from a tree will fly for some distance as well. All of these examples happen based on the laws and principles of physical science. Aircraft rely on these principles as well to overcome the effects and force of gravity to achieve flight. #### Lighter than Air Man's exploration of flight started with lighter than air craft, such as hot air balloons, which work on a buoyancy principle. These balloons float on the air much like a raft floats on water. The overall density of a hot air balloon is less than the air around it, and so it rises. However, unlike water, the density of air changes with altitude (more later), and so the balloon will rise until its density matches that of the air it floats in. If the air in the balloon is cooled, it becomes denser, and the balloon will sink. This allows for control of this type of aircraft. So lighter than air flight involves the balancing of two forces, lift (from buoyancy) and weight. #### Heavier than Air Heavier than air craft is more complicated, and involves the balancing of four physical forces: lift, drag, weight and thrust. We will look at these forces in detail. These forces fall under the study of physics, and an aviation technician needs to know these principles in order to understand why aircraft operate the way they do. ## Composition of the Atmosphere > [!aside]- Ref >[[AMT General Handbook Ch5_3#Composition of the Atmosphere|📘]] [[T101_1_002.png|➡]] As you will see, you need to have a rudimentary familiarity with a number of scientific topics in this field. The scientific category of fluids called gases is so fundamental to aviation that we must explore several aspects of gases. When you study engines, the actions of gases are critical to their function. In this lesson, we will concentrate on the fact that to understand how an aircraft moves through the [[atmosphere]], and how we can measure that atmosphere, we must have a basic understanding of the atmosphere itself. The atmosphere we live in is complex and always changing. Its ingredients change from day to day and vary from place to place. On average, at sea level, the main gases in the atmosphere expressed as a [[percentage]] are: - Nitrogen - 78% - Oxygen - 21% - Argon - <1% - Carbon Dioxide - <1% - Trace amounts of neon, helium, methane, krypton, and hydrogen, as well as water vapour As well as containing gases, it contains quantities of foreign matter such as dust and pollen. It might seem from this list that water vapour in the air is a very small and therefore unimportant component of the atmosphere. We will see later that this is absolutely not the case, and it can be argued that the water content of the air is the most important component of the atmosphere to aviators. ## Temperature > [!aside]- Ref >[[AMT General Handbook Ch5_2#Temperature|📘]] ### Kinetic Energy [[V T101 Temperature 1|📺]] Heat is a form of energy that causes molecules to move rapidly within a material. The amount of this shaking motion is measured in terms of temperature. So, temperature is a measurement of the [[kinetic energy]] of molecules.  [[T101_1_003.png|➡]] ### Different Scales of Temperature Temperature scales have been devised that measure temperature in degrees (°), but that have divided up the energy scale differently. #### Celsius %%==[[Master QB1#Q00524|Q]]==%% The [[Celsius]] scale is based on and refers to properties of water, which at its freezing point or melting point is 0°C and at its boiling point 100°C. This scale used to be known by the rather descriptive name Centigrade, (latin: centum=100, gradus=steps) but was named after Anders Celsius in 1948. This scale is used in most countries of the world and belongs to the metric system. One notable exception is the United States, which still uses Imperial measurement systems. In the USA, temperature is measured in degrees Fahrenheit. #### Fahrenheit %%==[[Master QB1#Q00492|Q]]==%% Daniel [[Fahrenheit]] did not use the freezing point of water as a basis for developing his scale. He called the temperature of an ice/salt/water mixture 'zero degrees', as this was the lowest temperature he could conveniently attain in his lab. He called his own body temperature '96 degrees', and then divided the scale into single degrees between 0 and 96. On this scale, the freezing point of pure water happens to occur at 32 (and the boiling point at 212). The Celsius scale has more convenient values for these phase transition points (0 and 100 degrees) because Anders Celsius used water as a basis for his scale. #### Kelvin %%==[[Master QB1#Q00493|Q]]==%% The Kelvin Scale uses exactly the same size degrees as Celsius. However, the Kelvin scale's starting point is different. Kelvin takes its zero to mean the lowest possible temperature. The fundamental particles whose motion we measure stop almost completely. In other words, nearly all molecular motion ceases. Note that this temperature is next to impossible to achieve. The equivalent temperatures in Celsius would be -273.15°C. Note also that the conversion from Celsius to Kelvin then would be to simply add 273.15. #### Rankine %%==[[Master QB1#Q00513|Q]]==%% The Rankine scale has a similar relationship to Fahrenheit degrees, that is, a Rankine degree is the same size as a Fahrenheit degree. Look at the diagram and see that the difference between absolute zero and the freezing point of water is the same number of degrees, and is also the case for the boiling point. Notice this for both Kelvin/Celsius and Rankine/Fahrenheit. The reason for these last two scales is for scientific and engineering work, when calculations require an absolute zero. Rankine is still used for Aerospace engineering in the US, reflecting its origins in Fahrenheit. ### Temperature in the Atmosphere %%==[[Master QB1#Q00512|Q]]%%==[[V T101 Temperature2|📺]] Temperature in the atmosphere decreases as we ascend, but it doesn't do so quite evenly. As we get to roughly 11 km (36,000 ft.) of altitude, the temperature does decrease fairly uniformly, roughly 2°C for every 1000 ft., but after that point, it remains almost constant at -55°C until an altitude of around 30 km (80,000 to 100,000ft.). Then the temperature begins to rise to a peak of around 15°C at approximately 50km (150,000 ft.). After the temperature stabilizes and levels out, it then descends again, to lows of around -100°C. At around 80km (250,000ft.) temperature once again transitions and begins to rise, eventually reaching highs as much as 2,000°C in the area of 400 to 600km of altitude. These temperature characteristics help us to define the atmosphere in layers. [[T101_1_004.png|➡]] ### Atmospheric Layers #### Troposphere %%==[[Master QB1#Q00508|Q]]==%% %%==[[Master QB1#Q00509|Q]]==%% %%==[[Master QB1#Q00510|Q]]==%% This is the layer closest to the surface of the earth where people can live unassisted, that is, without breathing apparatus. It is known as the lower atmosphere. Most of the mass of the atmosphere, 99% of the atmosphere's water vapour, and virtually all weather occurs within this layer. This is also the area where we can fly unprotected, that is, we do not require special protection from the radiation of the sun or other hazards of the universe. The troposphere is thicker at the equator, and gets thinner towards the poles, ranging in thickness from 6 to 20 km. At the very top edge of the troposphere is the tropopause, which forms the border between the troposphere and the stratosphere. The tropopause is an inversion layer, where air temperature ceases to decline with height and remains constant. #### Stratosphere %%==[[Master QB1#Q00507|Q]]==%% %%==[[Master QB1#Q00511|Q]]==%% On top of the troposphere is the stratosphere. This also signifies the beginning of the middle atmosphere, which continues into the next layer. At the upper layer of the stratosphere is the ozone layer which protects us from the harmful effects of solar radiation. The stratosphere extends to a height of roughly 50km. At the outer edge of the stratosphere is the stratopause, where temperature ceases to increase with altitude. See the [[T101_1_004.png|earlier diagram]] to see the temperature peaking at the stratopause. Like the tropopause just discussed, the stratopause is an inversion layer. With oxygen and pressurized cabins, man can fly in the lower reaches of the stratosphere, and in fact, we regularly do so in our larger airliners. The definitive electric guitar is the Stratocaster. #### Mesosphere %%==[[Master QB1#Q00491|Q]]==%% In the next layer, temperature decreases as altitude increases, and contains the coldest naturally occurring place on earth with temperatures dropping to as low as -100°C. Meteorites headed for earth encounter denser air with more molecules as they come into the mesosphere, and typically are destroyed by the heat of this friction. #### Thermosphere %%==[[Master QB1#Q00506|Q]]==%% In the highest layer of the atmosphere, also known as the upper atmosphere, air density is so low that there becomes less and less heat transfer, and solar emissions such as ultraviolet and x-ray radiation greatly affects temperature, which can rise to 2,000 degrees Celsius. Radiation from the sun causes particles in this layer to become electrically charged, affecting radiowave [[radio transmission|transmission]] and ostensibly causing [[Aurora Borealis]], known as the [[Northern Lights]], and [[Aurora Australis]], the [[Southern Lights]]. [🌍](https://www.space.com/astronaut-josh-cassada-aurora-photo-space-station) %% #JBTODO make glossary entry %% We are also learning that these emissions, particles and radiation have everything to do with Flight Safety! [[The Universe is hostile to Computers|🎞This video]] shows some problems we're having with our universe and our computers. There is some debate as to where the atmosphere ends. Some say that it is between 240 and 350 miles above the earth. Others say the edge of the atmosphere is between 600 and 6,000 miles. [[T101_1_005.png|➡]] Beyond the thermopause is the exosphere, and now we are essentially in outer space. Here, there are no molecules to absorb radiation from the sun, and so the temperatures plummet to 2.7K. You may see this described as an atmospheric layer, but the argument against this is that is the entire rest of the universe, that is external to the atmospheric layers just discussed, and not a layer itself. [[T101_1_006.png|➡]] ## Pressure and Atmosphere ### Pressure [[V T101 Pressure and Atmosphere|📺]] Pressure is a physical force that is exerted on or against something else. If you push a door, you are applying pressure to it. Pressure can be static or dynamic, that is, it can be moving or not. Our door example may have described a dynamic pressure, as the door moved as a result of our force. Pushing against a brick wall is an example of static pressure. ### Atmospheric Pressure > [!aside]- Ref >[[AMT General Handbook Ch5_3#Atmospheric Pressure|📘]] %%==[[Master QB1#Q00505|Q]]==%% We referred to heavier than air and lighter than air flight. Well, how heavy is the air itself? Atmospheric Pressure is the constant force that surrounds the earth due to the weight of the air around it. In order to answer the previous question, we need to know a bit about measuring pressure. ### Measuring Pressure #### Differential Pressure %%==[[Master QB1#Q00504|Q]]==%% Differential pressure is pressure measured between two different points. #### Absolute Pressure %%==[[Master QB1#Q00503|Q]]==%% Absolute pressure is pressure measured or referenced against a perfect vacuum. #### Gauge Pressure %%==[[Master QB1#Q00502|Q]]==%% Gauge pressure is pressure measured or referenced against the atmospheric pressure around the gauge or measuring instrument. ### Measuring Atmospheric Pressure %%==[[Master QB1#Q00497|Q]]==%% %%==[[Master QB1#Q00498|Q]]==%% %%==[[Master QB1#Q00522|Q]]==%% %%==[[Master QB1#Q00538|Q]]==%% %%==[[Master QB1#Q00501|Q]]==%% Atmospheric or Barometric Pressure is static pressure, and can be measured in a few ways. In the USA, Canada and Japan, inches of mercury ("Hg) is the standard measurement. The pressure or the weight of the [[atmosphere]] is compared to the weight of a column of mercury 1 inch (25.4mm) tall. Most other countries use Pascals (Pa). One inch of mercury is equal to 3.39 kPa. - Inches of mercury - "Hg - Pascals - Pounds per square inch (psi) The general standard of atmospheric pressure at sea level is 29.92 "Hg (inches of mercury). This can also be expressed as 101,325 pascals or 101.325 kPa. Expressed in pounds per square inch, (psi) it is 14.7 psi. If you could weigh a 1 inch square column of air at sea level extending to the top of the atmosphere, it would weigh 14.7lb. If you were to measure this column of air at a higher altitude, it would have less air above it, and thus it would weigh less. By comparing pressure at sea level to the pressure measured in an aircraft at altitude, calculations can be done to determine the flying altitude of the aircraft. You will learn more about this when you study altimeters (invented in part by Mr. Pascal) in aircraft instruments. ### Standard Atmosphere/Standard Day > [!aside]- Ref >[[AMT General Handbook Ch5_3#Atmospheric Density|📘]] [[AMT General Handbook Ch5_3#Standard Atmosphere|📘]] #### Atmospheric Density %%==[[Master QB1#Q00514|Q]]==%% %%==[[Master QB1#Q00515|Q]]==%% The density of the atmosphere diminishes rapidly with altitude, that is to say, it becomes much less dense the higher you go. At six miles of altitude, you can no longer breathe, and at 12 miles up, there is not enough oxygen to support combustion. The only aircraft that can fly that high have specially designed turbine engines. Air density is affected by what is in the air, its temperature, and the pressure that is exerted on it. Because the density of the [[atmosphere]] changes with altitude, if we are to measure or compute the performance of an aircraft, and then be able to compare it to other measurements, we need a standard reference condition. This standard is known as Standard Atmosphere or Standard Day, and is meant to represent approximately the average conditions existing at 40 degrees of latitude at sea level with the following assumptions: - Pressure: 29.92 "Hg - Temperature: 15 degrees C - Gravity: 32.174 fps/s (feet per second per second) [[T101_1_007.png|➡]] This standard is an [[ICAO]] (International Civil Aviation Organization) standard and has been adopted by most countries in the world. These parameters represent conditions at [[ASL|sea level]]. We saw that density decreases with an increase in altitude, and temperature varies throughout the layers. In addition to the three parameters already presented, the Standard Day includes viscosity information, which is the "thickness" of the air, which is affected directly by humidity. This property affects drag and lift, and therefore fuel consumption and aircraft performance, and thus is of interest to aviators. More on this later. ## Laws and Principles of Physics [[V T101 Laws of Physics1|📺]]It will be helpful for you to understand some scientific principles in order to understand how fixed wing and rotary wing aircraft fly. Here are a few that explain different aspects of aviation physics and technology: ### Boyle's Law > [!aside]- Ref >[[AMT General Handbook Ch5_2#Boyle’s Law|📘]] %%==[[Master QB1#Q00494|Q]]==%% %%==[[Master QB1#Q00495|Q]]==%% %%==[[Master QB1#Q00496|Q]]==%% Boyle's Law is one of the laws of physics that describes behaviours of gasses. When a gas is under pressure, it takes up less space. Boyle's law states in essence that the higher the pressure, the less the volume, and conversely, that the lower the pressure, the more volume will be taken up by the gas. This is subject to conditions of constant temperature and mass. We see this effect when a gas strut is compressed or expanded. [[T101_1_008.png|➡]] In this image, if you look at the centre cylinder, the volume and pressure both equal 1. In the left hand diagram, the pressure is increased by 2, resulting in a volume of ½. Conversely, in the right hand diagram, increasing the volume available to the gas molecules by 2 reduces the pressure by half. ### Charles' Law > [!aside]- Ref >[[AMT General Handbook Ch5_2#Charles’ Law|📘]] %%==[[Master QB1#Q00516|Q]]==%% Charles' law describes the relationship between the volume of a gas and its temperature given a constant pressure. It stipulates that volume is proportional to temperature.  [[T101_1_009.png|➡]]  [[T101_1_010.png|➡]] Notice in these diagrams the effect of temperature on volume and vice versa. In the first diagram, the temperature is low, and the volume is also low. See the graph in the upper right hand corner. In the second diagram, see that the temperature has increased, and so has the volume. In both cases, the pressure has remained constant. The line in the second diagram proceeding upwards diagonally is typical for a [[directly proportional]] relationship. As one axis increases, the other increases proportionally. ### Dalton's Law %%==[[Master QB1#Q00517|Q]]==%% [[V T101 Dalton's Law|📺]] Dalton's Law describes the relationship between the non-reacting components of a gas. This law is also known as Dalton's law of partial pressures. This law states that the total pressure of a gas is equal to the sum of the partial pressures of individual gasses. As we've seen, air is made of many gasses. In this diagram we see that the component gases that make up air are of different percentages, and thus, the pressures on these component gasses will differ. Dalton's law tells us that the pressure of the air will equal the sum of the pressures on the partial gasses. At standard atmospheric pressure (14.7PSI, 15°C) Nitrogen, being 78% of the total gasses, will represent 78% of the total pressure. 78% 14.7=11.5PSI. Oxygen, being 21% of the total will contribute 21% of the total pressure: 21% 14.7=3.1PSI [[T101_1_011.png|➡]] How does this apply to aviation? Well, in order to breathe, we need a certain minimum of oxygen. At 12,000 ft of altitude, the air pressure is 9.1 PSI, so the partial pressure of the oxygen component would be 1.9PSI. This is the maximum altitude humans can fly without the need for a pressurized cockpit or oxygen supplementation. The peak of Mt. Everest is 29,028 ft above sea level ([[ASL]]). Static air pressure is 4.5 PSI with a resultant .9 PSI for the oxygen component. This part of the earth is known as the death zone, as humans are severely starved of oxygen at these heights. ### Torricelli's Law %%==[[Master QB1#Q00518|Q]]==%% Torricelli's law describes the effects of pressure in a column. It explains the parting speed of a jet of water, based on the distance below the surface at which the jet starts, assuming no air resistance, viscosity, or other hindrance to the fluid flow.  [[T101_1_012.png|➡]] This diagram shows several such jets, vertically aligned, leaving the reservoir horizontally. In this case, the jets have an envelope (a concept also due to Torricelli) which is a line descending at 45 degrees from the water's surface over the jets. Each jet reaches farther than any other jet at the point where it touches the envelope, which is at a distance of twice the depth of the jet's source. The depth at which two jets cross is the sum of their source depths. Every jet (even if not leaving horizontally) takes a parabolic path. Toricelli's law is applied in engine technology, as well as for controlling airflow around an aircraft. ### Air Density #### Altitude vs. Density [[V T101 Air Density|📺]] As altitude increases, we know that the weight of the air above is less, and therefore, the air is less dense. #### Temperature vs. Density %%==[[Master QB1#Q00525|Q]]==%% We have also seen that, everything else being equal, if we increase the temperature of a gas, we will increase its volume (Charles' Law). Because volume and density are inversely proportional, we can conclude that an increase of temperature will cause a decrease in density. #### Density Altitude Because both of these relationships affect the density of the air and thus will affect the lift and drag of an aircraft, taking them both into account when calculating for flight gives a more accurate prediction of how an aircraft will perform. ### Effects of Air Density on Aircraft Performance > [!aside]- Ref >[[AMT General Handbook Ch5_3#Water Content of the Atmosphere|📘]] [[T101_1_013.png|➡]] #### Engine %%==[[Master QB1#Q00526|Q]]==%% %%==[[Master QB1#Q00527|Q]]==%% Decreased air density means that less air enters the engine of an aircraft. For reciprocal engines, each intake stroke has a fixed volume, dependent on the size of the pistons and cylinders. However, with less dense air, the engine will develop less power, and thus take off distances increase. For jet engines, less air also translates into less power with similar results. #### Airframe %%==[[Master QB1#Q00528|Q]]==%% %%==[[Master QB1#Q00529|Q]]==%% %%==[[Master QB1#Q00530|Q]]==%% Less dense air contains fewer molecules to interact with the aircraft wings and propellers. This reduces their effect. Also, true airspeed/ground speed increase with lower air densities, so the runway length required for landings and takeoffs increases. Sometimes aircraft weight restrictions are specified at higher density altitudes to prevent pilots from exceeding the limits of the aircraft in less dense air. ### Humidity > [!aside]- Ref > [[AMT General Handbook Ch5_3#Water Content of the Atmosphere|Ref]] %%==[[Master QB1#Q00531|Q]]==%% [[V T101 Humidity|📺]] We have seen that a small [[percentage]] of the air in our atmosphere is water. This water can be in the form of vapour or small droplets in suspension (fog). Formations of these small droplets are known as clouds. This water in the air is known as humidity, and, it may surprise you to know, weighs less than the air it is in. Water molecules are lighter than the nitrogen and oxygen molecules that form the majority of air. In fact, water vapour weighs approximately 62% of dry air. If that did surprise you, ask yourself why clouds, that is, concentrations of water vapour, float high in the sky. So, higher humidity air is less dense air and affects an aircraft much like an increase in altitude or temperature. #### [[Absolute Humidity]] [[Absolute Humidity]] is the actual amount of moisture in the air. Higher temperature air can hold more moisture. #### Relative Humidity [[T101_1_014.png|➡]] %%==[[Master QB1#Q00532|Q]]==%% %%==[[Master QB1#Q00533|Q]]==%% %%==[[Master QB1#Q00534|Q]]==%% Relative Humidity is the amount of moisture in the air relative to the maximum the air could carry. It is expressed as a percentage, i.e. 34%RH. Relative humidity has dramatic effects on performance. At 75%RH, the air is holding 75% of the maximum water vapour it can carry. But water vapour weighs 62% of air, so its density is considerably lower. Water vapour does not support combustion, so the effective air/fuel ratio decreases, the mixture becomes more rich. Piston engines can lose up to 12% of their power, turbines can lose up to 3%. #### Dew Point %%==[[Master QB1#Q00535|Q]]==%% When the air reaches a point where it cannot carry any more moisture, it is at 100%RH and moisture will condense out of the air as precipitation, i.e. rain or snow. Remember that air density is dependent on several factors, and a change in temperature can change the dew point. ### Bernoulli's Principle > [!aside]- Ref > [[AMT General Handbook Ch5_2#Bernoulli’s Principle|📘]] [[AMT General Handbook Ch5_3#Bernoulli’s Principle and Subsonic Flow|📘]] %%==[[Master QB1#Q00536|Q]]==%% %%==[[Master QB1#Q00537|Q]]==%% %%==[[Master QB1#Q00500|Q]]==%% [[V T101 Bernouilli|📺]] In order to understand how lift is generated, we have to look at the principle of pressure differentials as discovered by Daniel Bernoulli, a swiss physicist. Bernoulli's principle states: >As the velocity of a fluid increases, the static pressure of that fluid will decrease, provided there is no energy added or taken away. We consider air a fluid in this discussion. What Bernoulli's principle explains is the effect of air moving through a converging or diverging passage. It is called Bernouilli's principle because he was the one who discovered the principle of pressure differential of subsonic airflow as it applies over a wing. A little later we will look at the differences when we are looking at supersonic airflow. Put another way, within a confined system, total energy remains constant. If one component of energy increases, there must be a corresponding decrease in other components. The total pressure within a confined system is the total of static, that is stationary, and dynamic, that is moving, pressures. #### Mass Flow Rate %%==[[Master QB1#Q00539|Q]]==%% The amount of air molecules passing any given point per unit of time is constant through a tube or duct. This amount of air is known as Mass Flow Rate. Since the amount of air molecules remains the same, other parameters will have to change as the space changes. #### Converging Duct [[T101_1_015.png|➡]] %%==[[Master QB1#Q00540|Q]]==%% A converging duct's cross section gets progressively smaller from entry to exit. Any air that enters must exit; there is always the same amount of air in the duct, that is, the Mass Flow Rate is constant. As you see on the meters, the air exiting the duct has a higher velocity, and a lower pressure. #### Diverging Duct [[T101_1_016.png|➡]] %%==[[Master QB1#Q00541|Q]]==%% Notice that now the effect is reversed. As the duct becomes wider, the pressure on the air is more, but its velocity is reduced. In both of these cases, the total energy in the air has not changed. What is lost in velocity, which is a [[kinetic energy]], is gained in static pressure, which is [[potential energy]]. We do not need to go much farther than this, but understand that pressure and velocity have an [[inversely proportional]] relationship. #### Diverging and Converging Ducts [[T101_1_017.png|➡]] %%==[[Master QB1#Q00542|Q]]==%% Bernouilli's principle is shown here as a passage changes cross section from wide to narrow and back to wide. Note the readings on the dials, and the [[inversely proportional]] relationship between velocity and pressure. ### Newton's Laws of Motion [[T101_1_018.png|➡]] [[V T101 Newton|📺]] Newton's discoveries are also helpful to understand the physics that produce lift. Newton's laws are three physical laws that together lay the foundation for classical mechanics. They deal with the relationship between a body and the forces acting upon it, and its motion in response to these forces. #### Newton's Law of Inertia [[T101_1_019.png|➡]] %%==[[Master QB1#Q00543|Q]]==%% This law states that a body at rest will tend to remain at rest, and a body in motion will tend to remain in motion in a straight line until acted on by an outside force. In aviation, several examples demonstrate this. A rotor system prior to start is at rest, and it takes lot of energy to get it spinning at the required speed. Conversely, once a rotor is spinning, it wants to continue to spin and will take some force to slow it down. An engine overcomes resistance to movement by providing a means of outside force. [[T101_1_020.png|➡]] #### Newton's Law of Acceleration %%==[[Master QB1#Q00544|Q]]==%% Newton's second law states that the force required to produce a change in the motion of a body is directly proportional to its mass and the rate of change in its velocity. Imagine a ball travelling through the air towards you. How much force would it take to make it veer off to the left? Or how much force would it take to make it reverse direction and go back where it was coming from? Newton's law of acceleration says that you can figure out the force required by adding up the weight of the ball, how fast it's going and in which direction and how fast you change its direction. You would accept that a nerf ball coming at you at 15 km/hr could be deflected left with very little force. You would also naturally understand that a baseball coming at you at 90 mph would take a very strong hit with a bat to make it go back towards the pitcher. Newton's law of acceleration made it possible to actually understand and calculate exactly just how much force would be required in either of these cases. Don't worry, we will not be required to make these calculations, either on this course, or in your work as an aircraft technician. Acceleration is a change in velocity with respect to time. Acceleration can be either an increase or decrease in velocity. Typically we would refer to a negative change in velocity as negative acceleration or deceleration. #### Newton's Law of Action and Reaction [[T101_1_021.png|➡]] %%==[[Master QB1#Q00545|Q]]==%% Newton's Third Law states that when one body exerts a force on a body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body. When we look at lift, we will see that when a wing deflects air down, that body of air exerts a force upward and equal to the force of the air deflected down. We will see more on this a little later. In case the comic doesn't make sense to you, the dog understands Newton's Law of Action and Reaction in regards to the carbonated beverage he is seen shaking. He knows that the force created by the expanding bubbles in the drink will be counteracted when he opens the lid and the force meets the air. This dog is very smart, but he is not very nice. Newton's Third Law can be used to explain the concept of lift as well. Because wings typically fly with an angle of attack the air that gets deflected downward also generates lift by opposing the force of gravity. ## Conclusion In this lesson we looked at the following topics: - [[T101 Week 1#The Nature of Flight|The Nature of Flight]] - [[T101 Week 1#Composition of the Atmosphere|Composition of Atmosphere]] - [[T101 Week 1#Temperature|Temperature]] - [[T101 Week 1#Pressure and Atmosphere|Pressure and Atmosphere]] - [[T101 Week 1#Laws and Principles of Physics|Laws and Principles of Physics]] You can demonstrate your understanding of the material in this lesson by answering the questions in the corresponding weekly practice quiz correctly. > # [[t101 Home| ◀️ ]] &nbsp;[[T101 Home| Home ]] &nbsp;[[T101 Week 2| ▶️ ]] &nbsp; &nbsp; [[QR T101 W1| 🌐 ]] &nbsp; &nbsp;[[FB T101|Please Help]]