density - palo verde high school afjrotc...density of the surrounding fluid and the overall...

Science In Flight Unit 1

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Density

The density of an object is determined by the mathematical formula D = m/v, where D rep-resents density, M represents the total mass of the object, and V represents the total volume that the object occupies. In other words, an object’s density describes the average amount of matter that is contained within a standard unit of space. Because mass is usually measured in grams, while volume is usually measured in cubic centimeters (cm³, also called millili-ters), density is usually measured in grams per cubic centimeter (g/cm³).

Calculations – Density

1. Calculate the density of an object with a mass of 542 grams and a volume of 17 cubic centimeters.

2. Calculate the volume of a substance with a mass of 9.3 grams and a density of 15 g/cm³.

3. 2.8 L of substance has a mass of 3.5 kg. Calculate its density. (Hint: 1 L = 1000 ml, and 1 kg = 1000 g.)

Many ships that float on top of water are made of steel, yet steel is heavier than water. The walls of balloons and zeppelins are made of materials heavier than air, yet they float upward into the atmosphere. How is this possible? The answer lies in a comparison between the density of the surrounding fluid and the overall (average) density of the craft or other object. By filling the craft with a much less dense substance — like air in watercraft or helium in blimps — the overall density of the craft (including its contents) falls below the average density of the surrounding fluid, and the craft floats in the fluid.

Mini-Lab – Aluminum Boats

Materials needed:

Procedure1. Fill the bowl almost completely with water.2. Using one of the foil squares, place five paper clips in the center and tightly fold or

ball the foil around the paper clips. Carefully place the foil ball onto the water in the bowl. Observe.

3. Make a boat using the other foil square by folding each of the edges upward 1 cm, making sure to leave no holes or open seams. Place the other five paper clips onto the boat. Carefully place the boat onto the water in the bowl. Observe.

4. Without submerging the boat, carefully use the sewing needle to poke a small hole in the floor of the boat. Observe.

1. Wide, deep bowl2. Water3. 10 small metal paper clips

4. Two 5 cm x 5 cm sheets of aluminum foil

5. Sewing needle

Project “Excelsior”

While serving on Project Excelsior USAF Captain Jo-seph W. Kittinger, Jr set re-cords for highest balloon as-cent, highest parachute jump, longest freefall, and fastest speed by a man through the atmosphere. As part of research into high altitude bailout, he made a series of three parachute jumps wear-ing a pressurized suit from a helium balloon with an open gondola. The fi rst, from 76,400 feet (23,287 m) in November, 1959 was a near tragedy when an equipment malfunction caused him to lose consciousness, but the automatic parachute saved him (he went into a fl at spin at a rotational velocity of 120 rpm, the G factor calculated at his extremities was over 22 times that of gravity, set-ting another record). Three weeks later he jumped again from 74,700 feet (22,769 m). On August 16, 1960 he jumped from the Excelsior III at 102,800 feet (31,300 m) and was in freefall for 4½ minutes. He reached a maximum speed of 614 mph (988 km/h) before open-ing his parachute at 18,000 feet (5,500 m). Test results from his experience taught the USAF much about high altitude endurance.


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Buoyancy and Archimedes’ Principle

The tendency of an object to float on any fluid – liquid or gas – is called buoyancy. (From the same root word, note that a buoy is a device that floats on top of water as a marker for boats and for swimmers, or floats in the atmosphere as a marker for airplanes.)

From an insight made by an ancient Greek mathematician/scientist, Archimedes’ Principle states that the weight of the fluid displaced by an object is equal to the buoyant force pushing upward on the object. For example, if an ice cube is dropped into a glass of liquid water, the less dense ice cube will float, but some of the ice cube will lie beneath the original surface level of the water. To determine the buoyant force that is pushing upward on the ice cube, just weigh the water that is moved out of the way by the floating ice cube; the weight of that displaced water is equal to the buoyant force on the ice cube.

An object floats, or is said to have buoyancy, if the force of gravity pulling downward on the object is less the buoyant force pushing upward on the object. An object’s weight is the mass of the object multiplied by the accelerating force of gravity pulling downward on the object (generally, the accelerating force of gravity is approximately 9.8 m/sec² or 32 ft/sec² at or near the surface of Earth).

The ice cube described above floated because its weight was less than the buoyant force of the water pushing upward on it. On the other hand, the ice cube sinks (falls to the ground) when placed into mid-air because the weight of the ice cube is greater than the buoyant force exerted by the air. Ultimately, buoyancy is an issue of relative weights of the object and the surrounding fluid. Since weight is tied directly to mass and density, the denser an object is, the more it will weigh, therefore it will be less buoyant.

Mini-lab – Freshwater versus Saltwater

Materials needed:

Procedure1. Weigh egg. Weigh 2 empty cups, and mark them A and B. Record weights.2. Completely fill one unweighed drinking cup with water. Place the cup onto the pie pan to catch overflow-

ing water. Gently lower the egg into water. Observe. Pour the water that spilled onto the pie pan into Cup A. Weigh Cup A containing the displaced water. In order to calculate the weight of the displaced water, subtract the weight of the empty Cup A from the weight of Cup A with the water. Record the weight of the displaced water. Compare the weight of the displaced water to the weight of the egg.

3. Fill pitcher more than half-full with water. Stir in salt until saturated.4. Repeat step 2 using the other unweighed cup, saltwater mixture, and Cup B.

1. Uncooked egg in shell2. 4 drinking cups3. Large (1 L or larger) pitcher4. Water

5. Salt (NaCl)6. Stirring rod or spoon7. 2 aluminum pie pans



Lab – Density and BuoyancyMaterials needed:

Procedure:1. Carefully place the steel bolt, the polyethylene pen cap, and the piece of balsa wood into the large beaker.2. Pour the water into the small beaker. Stir in five drops of food coloring.3. Slowly pour the colored water into the large beaker, and observe.4. One at a time, slowly pour the corn syrup, then the vegetable oil, and then the ethyl alcohol into the

large beaker. Allow mixture to settle before adding the next solution. Observe after each pour.5. Gently stir to mix the contents of the large beaker. Observe.

Data: Complete the following table.

Analyses:1. List the following objects and substances in the order that they came to rest, starting at the top of the

large beaker and ending at the bottom of the large beaker: steel bolt, pen cap, balsa wood, water, alco-hol, oil, and corn syrup.

2. How is your answer to question 1 related to the densities in the table above?3. What do you know about the density of air based on this experiment?

Conclusion:Explain how density of fluids (and solid objects placed into fluids) affects buoyancy.

Extensions:1. Frozen water floats on top of liquid water. Explain how density of water changes when water undergoes

the physical change of freezing or melting.2. Research the densities of helium and atmospheric air. Explain why both float on water. Also, determine

how much helium is needed to float a foil balloon in air if the uninflated balloon has 24.3 g of mass and 2.8 cm³ of volume.

1. Large (1000 ml) glass beaker2. Small (400 ml) glass beaker3. Stirring rod or spoon4. 2 cm³ piece of balsa wood5. Polyethylene plastic pen cap6. Small steel bolt

7. 200 ml distilled water8. Food coloring (dark red or blue)9. 200 ml ethyl alcohol10. 200 ml vegetable oil (of a distinguishable yellow

color)11. 200 ml corn syrup

Object/Substance Density (in g/cm³) Location (1 = top, 7 = bottom)Corn syrup 1.38

Ethyl alcohol 0.79

Vegetable oil 0.82

Water 1.00

Steel 7.81

Balsa wood 0.12

Polyethylene plastic 0.92



Fluid Pressure, Bernoulli’s Principle, & Lift

Pressure is the amount of force exerted on a surface. Generally, pressure is measured in the U.S. using pounds per square inch (psi) or atmospheres (1 atm = 14.6956 psi ), and in the metric system using pascals (1 Pa = 1 Newton of force per square meter, or 1 N/m²).

Based on the observations of a Swiss scientist in the 1700s, Bernoulli’s Principle states that as the speed of any fluid — liquid or gas — increases, the pressure in that fluid decreases. This occurs because the fluid becomes relatively less dense than its surroundings, causing it to “float” ahead of or above more dense substances. This phenomenon creates slipstreams for bicyclists and birds (drafting for racecars) to closely follow behind their leaders with less air resistance.

Mini-lab – Bernoulli under a funnel

Materials needed:

Procedure:

Add to Bernoulli’s Principle the notion that nature abhors (hates) a vacuum and you’ll understand why dust and leaves seem to “chase” a quickly passing truck down the street. You’ll also see the beginning of controlled flight!

When the force of lift is greater than the weight of the plane (caused by gravity pulling the plane’s mass downward), the plane rises. When the force of lift is less than the weight of the plane, the plane falls. Lift is accomplished using Bernoulli’s principle. A plane’s wing – called an airfoil – is curved more severely on the top than on the bottom. Therefore, air passing around the wing must travel faster to cover the greater distance over the top of the airfoil than across the bottom. This results in lower air (fluid) pressure above the wing, and the wing is pulled upward (lifted) to fill the pressure gap.

1. Ping pong ball2. Flat table or floor

3. Transparent funnel large enough to lie face-down over top of ping pong ball with little extra room

WING

LOWER AIR PRESSURE REGION

NORMAL AIR PRESSURE REGION

Scientists study different shapes of airfoils to address the speed and the directional control of airplanes.

1. Place a ping pong ball on a flat table-top (or on the floor).

2. Place a funnel with its large mouth face-down, centered over the top of the ball, flat on the tabletop.

3. Blow as hard as possible through the small drain hole in the funnel. Observe the ping-pong ball as you blow.

The “Predator”

The 11th Reconnaissance Squadron became the fi rst Air Force unit to operate the Predator, or MQ-1, an unmanned aerial vehicle designed for aerial surveil-lance and reconnaissance. The Predator is a medium-altitude, long-endurance, re-motely piloted aircraft. The MQ-1’s primary mission is interdiction and conduct-ing armed reconnaissance against critical, perishable targets. The MQ-1 Predator is a system, not just an air-craft. The fully operational system consists of four air vehicles (with sensors), a ground control station (GCS), a Predator primary satellite link communication suite, and 55 people. It can serve in a reconnaissance role, and it can also be weap-onized and can carry and use two missiles. The aircraft has been in use since 1995, and been in combat over Af-ghanistan, Bosnia, Kosovo, Iraq, and Yemen. Since its creation, the Air Force fl eet of Predators has performed missions that were once ex-ecuted by attack helicopters or ground troops such as scouting battlefi elds, track-ing the enemy, and launch-ing quick, precise strikes. The Predator program has saved the lives of countless U.S. soldiers while hitting targets that manned aircraft could not get close enough to reach.



Airplane FlightFour forces work together to determine whether an airplane rises or falls through the air: thrust, drag, lift, and gravity. Thrust is the force that pushes or pulls a plane forward through the air. Propellers, jet engines, tailwinds, and other outside sources – even catapults! – can provide needed thrust. Without enough thrust, air won’t move past the plane quickly enough to create lift. Drag is the force that resists forward motion and acts against thrust. Drag is created primarily by friction between the plane and the atmosphere. If the force of drag is too great, then a plane will move slower and will lose lift. Earth’s gravity pulls the plane downward, giving the plane weight. As described on the previous page, when the force of lift exceeds the plane’s weight, the plane rises.

Modern airplanes are sophisticated machines with thousands of moving parts. The propellers, the jet engines, or the rock-et engines provide thrust for the plane. The wings are shaped like airfoils to create lift using Bernoulli’s Principle. The elevators are hinged, horizontal surfaces attached to the back of the tail of the plane. Elevators control the plane’s movement upward or downward. When the elevators are raised, the tail is forced downward, the wings are forced upward, and the plane climbs. The ailerons are hinged, horizontal surfaces attached to the back, outer edges of the wings of the plane. The ailerons are used to turn the plane. As one aileron rises, the opposite aileron lowers, raising one wing and lowering the other, tilting (or banking) the plane toward the lower aileron. The rudder is a hinged, vertical surface attached to the tail of the plane that helps the plane enter and recover from turns by swinging the tail to the left or right.

Mini-lab – Paper airplane designs

Materials needed:

Procedure:1. Fold a long paper airplane.* Launch the airplane. Observe its flight.

2. Use the scissors to cut flaps at the tail end of the plane. Fold one flap upward and one flap downward. Launch the airplane. Observe its flight.

3. Fold both flaps upward or downward. Launch the airplane. Observe its flight.

4. Repeat the above steps using a short paper airplane.* Repeat the above steps with other modifications to the airplanes and other airplane designs.

*Log on to educationinflight101.com for printable, sample paper airplane instructions.

1. Crisp paper without holes 2. Scissors

Science In Flight Quiz


Name __________________________________ Date __________ Class period _____

Quiz – Fluid Pressure and Flight

1. Which of the following is true regarding an object with a volume of 28 cm³ and a mass of 35 g?a. It has a density of 0.8 g/cm³ and will float in

pure water.b. It has a density of 0.8 g/cm³ and will sink in

pure water.c. It has a density of 1.25 g/cm³ and will float in

pure water.d. It has a density of 1.25 g/cm³ and will sink in

pure water.

2. According to Archimedes’ Principle, if a floating object displaces 35 lbs. of water, what is the buoyant force acting on the object?a. Exactly 35 lbs.b. Less than 35 lbs.c. More than 35 lbs.d. Not enough information given

3. Steel is denser than water. Which of the following doesn’t explain how a steel ship floats on water?a. The water that the ship displaces weighs more

than the ship weighs.b. The ship is partially filled with air, making its

overall density less than the overall density of the surrounding water.

c. Pure steel is buoyant in seawater because of Archimedes’ Principle.

d. The buoyant force pushing up on the ship is greater than the force of gravity pulling down-ward on the mass of the ship.

4. Which of the following correctly describes how Bernoulli’s Principle helps an airplane to achieve lift?a. Low air pressure below the wings of the plane

pushes the plane upward.b. High air pressure above the wings of the plane

pulls the plane upward.c. Low air pressure above the wings of the plane

pulls the plane upward.d. Thrust moves the plane fast enough that the

force of gravity becomes zero.

5. On the diagram below, label the four main forces that affect a plane’s ability to fly:

6. For each description below, write the name of the corresponding airplane part.

a. Horizontal flaps attached to wings that are used for turning:

b. Components shaped like airfoils to provide lift:

c. Horizontal flaps attached to tail that control ascent and descent:

d. Vertical tail flap that assists with entering and recovering from turns:



HelicoptersThe roots of the helicopter date back at least as far as the 15th century drawings of Italian artist and inventor Leonardo da Vinci. Today, helicop-ters can carry thousands of pounds of cargo, weaponry, and passengers over long distances with superb control, but the key mechanics of the helicopter haven’t changed much.

A helicopter’s rotor blades create lift essentially by screwing into the air much the same way that a metal screw slices and pulls forward into solid matter. Taking advantage of Bernoulli’s Principle, a lower-pressure region is generated on one side of the blades, and the blades are pulled into that region. Basically, a helicopter rotor is very much like an airplane propeller, pulling its aircraft along by utilizing pressure differentials on the two sides of the airscrew. Because a helicop-ter’s rotor pulls its vehicle upward while the force of gravity pulls the craft downward, a helicopter has a distinct advantage over most winged airplanes: the capability to hover in place by creating a net vertical force of zero.

Mini-Lab – Aluminum Boats

Materials needed:1. Paper2. Goggles3. Table4. Large box fan (the plug-in type used to cool a room while it stands vertically)

Procedure1. Clear the table top of debris. Stand the fan in a stable position upon the table.2. Plug in the fan. Turn on the fan. (Variable fan speeds may enhance this lab.)3. Release a piece of paper vertically a few inches behind the fan. Observe.4. Repeat step 3, this time releasing the paper in front of the fan.5. If the fan has variable speeds, repeat steps 3-4 on the different speeds. Observe the results.

A pilot can control the tilt (or pitch) of the rotor blades to move a helicop-ter in almost any direction. Just as a toy kite gains lift by tilting through moving air, so does tilting a helicopter’s rotor blades create lift for the aircraft. However, unlike a kite, a helicopter must move itself through moving air rather than taking advantage of air naturally flowing past it. Thus, lesser pitch in the blades decreases lift, and gravity may pull the helicopter downward. However, a helicopter can rise straight upward with great stability. By tilting the entire saucer created by the spinning of the rotor blades, a helicopter pilot can make the vehicle move forward, back-ward, or sideways, even while ascending or descending through the air.

Additionally, control over the pitch of the smaller set of revolving vertical blades near the tail helps to turn or keep the helicopter straight. Such maneuverability is the other major advantage that helicopters have over most other winged aircraft.



Basic Jet EnginesNearly two thousand years ago, Hero of Alexandria invented a spectacular novelty – the aeolipile – a device that uses two jets of steam to spin a sphere … but few practical applications were developed from his creation for many centuries. Today, a jet engine is any mechanical device that discharges a jet of fast-moving fluid (liquid, gas, or plasma) to generate a force of thrust. Technically, this category includes water jets, ramjets, and rockets, though the term “jet engine.” However, modern vernacular usu-ally is limited to gas-turbine engines like turbojets and turbofans that propel airborne vehicles by using a continuous series of compression and exhaust activities.

If you release an open-nozzle balloon filled with compressed air, a jet of air rapidly escapes through the nozzle, and the balloon travels in the opposite direction. The escape of air is an action, and the balloon’s movement is a reaction. Isaac Newton described this in his Third Law of Motion – every action has an equal and opposite reaction.

Mini-Lab – Balloon Jet* Note: This Mini-Lab can be enhanced by repeating the steps with changed factors, like

amount of air in balloon, attached weights, or slope of string. For such increased levels of experimentation, mathematical relationships should be calculated with various specific measurements – time of flight, mass, circumference of balloon, etc.

Materials needed:1. Rubber balloon2. Plastic drinking straw3. Tape4. Kite string or fishing line

Procedure1. Thread a long piece of string through the straw. Tie the ends of the string to two

places far apart (at least three meters) from each other so that string is taut.2. Inflate balloon and pinch nozzle shut with fingers. (Don’t tie nozzle.) Tape balloon

to straw, aligning nozzle with string. Release balloon. Observe.

In all types of jets, air is drawn into a combustion chamber, compressed, mixed with injected fuel, and ignited. Rapidly-expanding gases created by the burning of the mixture rush out of the rear nozzle. This action generates the reaction of forward movement.

A ramjet has few moving parts. Air is compressed in a ramjet by the plane’s forward move-ment, which means that a ramjet only can work when the plane is moving. Thus, a “moth-ership” has to launch a ramjet plane. A pulsejet is only slightly more sophisticated, having an inlet valve that controls the amount of air intermittently entering the engine.

The “Minuteman”

The Minuteman was the world’s fi rst solid-fueled Intercontinental Ballistic Missile (ICBM), and has been the mainstay of the Air Force’s ICBM force from its inception. Solid-fueled rockets have obvious advan-tages when compared to liq-uid-fueled ones. The most important advantage was being the long storage life of the motors and the lack of a time-consuming and poten-tially dangerous fueling pro-cess. Despite diffi culties in the design process, progress was made, and by mid-1957, pre-development studies for a solid-fueled ICBM were fi rmly under way. In Feb-ruary 1958, the Minuteman program was offi cially ap-proved, and three years later, on Feb 1, 1961, a Minuteman ICBM launched for the fi rst time at Cape Canaveral in a major test. Under full guid-ance, the solid-fueled mis-sile can travel 4,600 miles and hit the target area.



Turbojets, Turboprops, and TurbofansThe primary parts of gas-driven turbojet engines are enormous sets of fans called turbines. Facing the front of the airplane, the first set of turbines is the turbo-compressor, which draws a large volume of air into the front of the engine by spinning to take advantage of Bernoulli’s Principle. The air molecules then are forced into narrow tubes, where the air molecules are extremely compressed and heated.

The hot, compressed air next enters the combustion chamber in the middle of the engine, where the air is mixed with jet fuel that is sprayed into the chamber by a fuel injection system. The heat of the air (often assisted by an electrically-generated spark) ignites the fuel, which produces even greater levels of heat and pressure in the chamber. As the hot gases expand within the combustion chamber, their only path of escape is to blast out the exhaust nozzles at back of the turbojet engine.

Before escaping through the nozzles, however, the superheated and pressurized gases pass through a bladed turbine wheel. The turbine wheel then turns

the main shaft, which operates the front compressor, increasing efficiency of the engine by capitalizing on the gases’ high velocity, which the engine created in the first place.

Additionally, some aircraft – especially supersonic planes – employ afterburners before the jet of high-velocity gases fully leave the engine. These devices burn any remaining traces of unused jet fuel at extreme temperatures (exceeding 1600°C or 3000°F), thus expanding, pressurizing, and accelerating the gases to generate even greater force as they are pushed outward through the nozzles at the rear of the engine. The resul-tant force of the exhaust provides the action against which the plane is thrust forward in reaction, following Newton’s Second and Third Laws of Motion (see pages 13 and 14).

While turbojet engines accelerate a small mass of air by a large amount, propellers accelerate a large mass of air by small amount. Turbojets, accordingly, are used pri-marily to provide thrust for faster aircraft that travel rel-atively long distances. On slower (especially subsonic)

or shorter-flight aircraft, turboprop engines that use a gas turbine-pow-ered propeller are more common.

Jet engines on most mod-ern aircraft today belong to the even more sophis-ticated category of tur-bofan engines. In these engines, the turbocom-pressor not only acts as an intake fan, but also provides airflow to a bypass duct that sends its less heated air outside the compression cham-ber to cool the turbine blades and vanes to pre-vent melting.

Reaction

Compressor

AirIntake

Fuel Injector

Shaft

Combustion Chamber

Action

Nozzle

Turbine



Rockets & Newton’s 3rd Law of MotionAt least 800 years ago, the people of China had mastered the basics of solid-fuel rockets in the form of gunpowder-propelled fireworks that carried colorful-burning chemicals in casings of bamboo and paper. Today, rocket engines also drive supersonic planes, carry satellites into orbit around Earth, propel weaponry missiles, and launch humans and their creations into outer space, but the basic mechanics of rockets haven’t changed much.

If you throw a baseball forward while standing on a skateboard, you will roll backward with a force equal to that of the thrown ball. Your throw is an action, and your roll on the board is a reaction. Similarly, when you fire a gun, the explosion of the gunpowder or other propel-lant in the chamber of the gun forces the bullet forward out of the barrel and slams the gun backward into your body. English mathemati-cian and scientist Sir Isaac Newton described this event in his Third Law of Motion – every action has an equal and opposite reaction. Rocket flight is based on this principle.

Some rockets use solid fuels, often including black gunpowder and a substance that is mainly rubber. Starting with the 1926 experiments of

Robert Goddard, many other rockets – includ-ing several of the rockets that drive launch craft, orbital craft, planes, and missiles employed by the U.S. Air Force – use various liquid fuels. The most common of these chemicals are hydrogen peroxide (H2O2), various forms of alcohol and gasoline, and liquefied forms of hydrogen, fluorine, or liquid oxygen main-tained under extreme pressure and temperature conditions. The advantage of liquid fuel over solid fuel is control over thrust; solid fuels burn completely once ignited.Gases created by the burning of such propel-lants try to rush outward in all directions within the thrust chamber of a rocket, but the gases are released only through the exhaust nozzle. This exhaust is the action which, by Newton’s Third Law of Motion, generates the reaction of thrusting the craft forward or upward. The dif-ference, though, between a rocket engine and a shotgun is that the shotgun must throw only a single ounce of mass approximately 700 miles per hour. Indeed, 700 miles per hour is much faster than your arm can throw a baseball, but the amount of force exerted by a firing shot-gun can’t drive a multi-ton supersonic aircraft through the atmosphere, especially for a sus-tained run.

The necessary difference between a shotgun’s mechanism and the engine of a rocket ship lies primarily in the fuel mix-ture. The typical mixture for single-explosion gunpowder is 75% nitrate, 15% carbon, and 10% sulfur. A slight tweaking of this recipe to 72/24/4 can produce a decent rocket fuel that can generate a rapid yet sustained burn. Of course, far more sophisticated chemical combinations are used in mod-ern high-powered rocketry.

97 10 12

11

13 15 17654321

8

14 16

Diagram of V-2 rocket components: 1. nosecone; 2. automatic gyro control; 3. guidebeam & radio command receivers; 4. alcohol-water mixture; 5. rocket body; 6. liquid oxygen; 7. hydrogen peroxide tank; 8. compressed nitrogen pressurising bottles; 9. hydrogen peroxide reaction chamber; 10. propellant turbopump; 11. oxygen/alcohol burner caps; 12. thrust frame; 13. rocket combustion chamber; 14. wing; 15. alcohol inlets; 16. jet vane; 17. air vane.

Titan I Missile

The U.S. Air Force suc-cessfully launched the fi rst Titan I missile with a range of 5,500 nautical miles. The two-stage liquid-fueled mis-sile was deployed in under-ground silos and was raised to the surface for launching. The Titan I burned RP-1 (Refi ned Petroleum 1, a highly refi ned form of kero-sene similar to jet fuel) and LOX (liquid form of oxy-gen.) Testing of the missile was completed in 1960 and the missile was deployed in 1961. The missile utilized both radio and all-inertial guidance. The Titan was the fi rst Inter-Continental Ballistic Missile, or ICBM, with two distinct stages of differing diameters. When the fi rst stage had fi nished consuming its propellant, it dropped away, thereby decreasing the mass of the vehicle. That made for a more effi cient missile, which resulted in increased range and enabled a larger payload. At a cost of $1.5 million a piece, two versions of the U.S. Air Force’s Titan were deployed. The Titan I stood at the forefront of United States security dur-ing the Cuban Missile Crisis and was removed from ser-vice in 1965, in favor of the Titan 2.



Rockets and Newton’s 2nd Law of Motion

Rockets designed to launch their payloads into outer space beyond Earth’s atmosphere require huge amounts of force from their engines, but even smaller craft on lower trajecto-ries still need enormous amounts of force. Sir Isaac Newton’s Second Law of Motion states that the force exerted by an object is the product of that object’s mass and its acceleration, or F = M A.

Calculations – Force

1. Calculate the force (in Newtons) needed to accelerate a 3.2 kg ball by 25 m/s².2. How fast could a 100 N force accelerate a 5 kg mass? A 10 kg mass? A 20 kg mass?

Describe the pattern.

The amount of force that would be needed to keep a one pound object stationary in air near the surface of Earth is called one pound of thrust. Gravity near the surface of Earth acceler-ates objects downward toward the center of Earth at approximately 32 feet per second each second (or 32 ft/s², which is equivalent to 9.8 m/s²), or roughly 21 miles per hour each sec-ond (21 mph/s). Therefore, in order to produce one pound of thrust, an engine must create a force of that size. For example, if you threw a one pound rock at a velocity of 21 miles per hour (or 32 ft/sec or 9.8 m/s), you would produce one pound of thrust … but only once and only for a split-second. To maintain just one pound of thrust force, you would have to continuously throw a one pound rock at a velocity of 21 miles per hour every second! In order to produce two pounds of thrust force, you would have at least these choices:

• Throw a two pound rock at a velocity of 21 miles per hour every second,• Throw two one pound rocks at a velocity of 21 miles per hour every second, or• Throw a one pound rock at a velocity of 42 miles per hour every second.

Rocket ships, rocket planes, and rocket-driven missiles weigh between dozens of pounds and thousands of tons. Thus, the amount of thrust needed to launch such items into outer space or to drive them through the atmosphere is far greater than the thrust needed to throw a small rock. For an object to overcome Earth’s gravity and travel to outer space, its rocket must produce enough thrust to reach and maintain an escape velocity of nearly 25,000 miles per hour (40,000 kph). Such efforts require enormous amounts of fuel.

According to Newton’s Second Law of Motion, force equals mass times acceleration. When fuel burns, the fuel’s mass in solid or liquid form is the same as the mass of the gases made after combustion according to the Law of Conservation of Mass. Therefore, rockets must carry very large amounts of fuel mass and must tremendously accelerate the mass of that fuel through chemical combustion reactions in order to generate the desired thrust. Just imagine how much mass must be used simply to produce enough force to drive a 150-pound pilot for 10 minutes, and you’ll understand why many rocket-driven vehicles carry dozens of times more mass in fuel than the weight of their payloads.

Project “SCORE”

On December 18, 1958, the U.S. Air Force placed in orbit the fi rst artifi cial com-munications satellite using the four-ton Atlas launcher. The entire rocket was placed into low orbit with the com-munications equipment inte-grated into the fairing pods of the missile. The low orbit limited life expectancy of the satellite to only two to three weeks, thus limiting oppor-tunities for real-time relay between the two ground sta-tions. Therefore, a store-and-forward mode was added by including a tape recorder, which also gave the satel-lite a worldwide broadcast capability and the world’s fi rst satellite to broadcast voice. The next day, De-cember 19, 1958 the satellite broadcasted a taped record-ing of President Dwight D. Eisenhower’s Christmas message. The SCORE sat-ellite, an acronym for Signal Communication by Orbiting Relay Equipment. SCORE as a research endeavor was an experiment designed to test the feasibility of trans-mitting messages through the upper atmosphere from one ground station to one or more ground stations. The result of the project was unquestionably a major sci-entifi c breakthrough which proved that active communi-cations satellites could pro-vide a means of transmitting messages across the band-width from one point to any other on the planet Earth.



Lab – Pop rockets

Materials needed for each lab group (teams of two or three students):

* The film canister should be of the plastic type in which the cap tucks inside the canister.

Procedure

Data: Complete the following table once for each attempted launch.

Design details Time of fl ight (in seconds) Other fl ight observations

Analysis:1. Describe patterns in your observations based on the changes in your design.2. Use the formula for parabolic flight to calculate how high your rocket flew based on each time-length of

flight.

Conclusion:1. Compare and contrast your pop rocket with a large aircraft rocket.2. Research and describe the chemical reactions in your “rocket fuel.”

Extension:How would the results have been different if vinegar had been used instead of water?

1. 35-mm film canister*2. 2 – 3 effervescent antacid tablets, each cut into

halves3. Several pieces of paper4. Scissors5. Cellophane tape

6. Water7. Stopwatch8. Small coins or other small attachable weights9. Goggles for each lab member10. Wide space outside away from trees, buildings,

etc., with a hard, flat floor (like a sidewalk)

1. Using paper, scissors, and tape, assemble a nosecone and an open-cylinder body around the outside of the film canister, leaving the open end of the canister facing downward (away from the nosecone) so that “fuel” can be added later. Choose your own design details (length of nosecone, length of rocket body, shape and number of fins, etc.). Record the design details.

2. Turn the rocket upside-down. Carefully pour water into the film canister, filling approximate-ly 1/2 of the canister’s volume without wetting the paper.

3. Quickly perform these steps: Drop into the canister a half-tablet of the effervescent antacid.

Close the canister by inserting the lid. Place the rocket right-side-up onto the hard floor, and back away before the rocket launches.

4. Have a lab partner (other than the launch master) time the flight of the rocket using the stopwatch. Observe the flight, and record observations (including amount of time that the rocket was off the ground).

5. Collect the rocket, disassemble the paper body, and repeat the above steps after changing a design detail. Perhaps attach extra weights (small coins), change the amount of water in the rocket, or change the paper body structure.

6. Repeat several more times, making other changes to the rocket.



Sound waves: The Doppler EffectSound is created when matter vibrates at a frequency that can be interpreted by a receiving device (like the human ear). As the frequency of vibration increases, the pitch of the sound grows higher. For example, a middle C note on a piano is created when the key’s hammer strikes a string that is tuned to vibrate at 261.64 hertz (vibrations/sec), while the string of the slightly higher D note vibrates at a somewhat faster 293.68 hertz.

You may have noticed that as fast-moving objects like cars and airplanes rush past your ear, their pitch changes from a higher note (as the object approaches your ear) to a lower note (as the object moves past and away from your ear).* This phenomenon, the Doppler Effect, occurs because the sound waves created by the moving object are emitted closer together in front of the moving object and farther apart behind the moving object.

* The Doppler Effect is not an issue of loudness. Though airplanes seem to grow louder as they approach and quieter as they leave, that change in volume is caused simply by diffu-sion of energy between the airplane engines and your ear. The more distant the airplane is, the greater the loss of energy is before the sound reaches your ear.

As an airplane moves forward while making a continuous sound, the airplane “chases” its own waves, and each new sound wave is bunched closely behind the previous wave. When the compressed waves hit your ear, your ear receives them rapidly after one another, or at a higher frequency. Behind the airplane, the waves are spread farther apart as the airplane “runs away” from the backward-moving compo-nent of each wave. The result is that the waves behind the plane reach your ear at a lower fre-quency.

Note that the airplane pilot doesn’t hear a Doppler Effect from the engines of his own plane because the pilot remains the same dis-tance from the engine throughout the flight.

Mini-Lab – Doppler in Water

Materials needed:1. Large rectangular baking pan2. Water

Procedure:1. Pour water into the baking pan about 1 inch deep. Let the water settle flat.2. Beginning at one end of the pan, tap your finger vertically into the bottom of the

pan and vertically back out of the water again. Repeat the taps in a straight line toward the other end of the pan without tapping beyond the expanding waves.

3. Observe the waves hitting the pan walls in front of and behind your finger.

The Doppler Effect For A Moving Sound Source

Small WavelengthHigh Frequency

Long WavelengthLow Frequency

Moving Source

X-1 “Glamorous Glennis”

USAF Captain Charles E. Yeager at Muroc Air Base, California marked the fi rst faster-than-sound fl ight, in a rocket-powered research plane, Bell XS-1 rocket ship. Captain Yeager was a decorated WWII pilot who remained with the Air Force after World War II as a test pilot. Captain Yeager broke the sound barrier on October 14, 1947, fl ying the experi-mental X-1 at Mach 1 and an altitude of 45,000 feet (13,700 miles). Captain Yea-ger’s fl ight recorded Mach 1.06. Yeager made another 21 fl ights in the X-1 after the fi rst supersonic fl ight. None of them were routine. But perhaps the most signifi cant would be his fl ight of Janu-ary 5, 1949, the fi rst ground launch. Firing all 4-rocket chambers simultaneously, the X-1 streaked off down the runway. After about 1500 feet, Yeager raised the nose at 200mph and the X-1 jumped into the air. The X-1 was accelerating so fast that when he fl ipped the gear handle up, the actuating rod snapped off and the wing fl aps blew off. Only 80 sec-onds after ignition, the X-1 was at Mach 1.03 and 23,000 feet. Yeager set a time to climb record to 20,000 feet that would stand for some time. Capt. Yeager’s X-1 is on display at the Smithson-ian Institution’s National Air and Space Museum.



Sound waves:Mach number and sonic booms

The speed of sound in dry air generally is described as v = 331.4 + T (m/s), where T represents Celsius tempera-ture. Molecules in warmer air vibrate faster and, therefore, are more often nearer to one another, increasing the rate at which sound energy can be transferred from one air molecule to the next air molecule. Thus, at 0°C sound travels through dry air at approximately 331.4 m/s (or 742.336 miles per hour), while at 20°C the speed of sound in dry air is a slightly faster 343.6 m/s (or 769.664 mph). Humidity and pressure both affect air density, and so they also affect the speed of sound through air.

Velocity of a very fast aircraft is described using Mach number, which tells how many times the speed of sound (at 0°C) an object is moving. For example, a plane traveling at Mach 5.1 has a relative velocity of 331.4 × 5.1 = 1690.14 meters per second.

For many years, airplane pilots and engineers believed that the so-called “sound barrier” could not be broken. This doubt arose from failed attempts to fly aircraft at supersonic speeds, as planes vibrated violently and some-times fell out of control. Today we know that most of the problems at speeds near the sound barrier were cre-ated by a phenomenon called the compressibility effect. This effect occurs at flow speeds above 250 mph (and

is particularly noticeable near Mach 1) as some of the energy of the aircraft compresses the air and changes its density, thereby altering the amount of drag on the aircraft.

When humans finally broke the sound barrier, a new phenomenon burst onto the scene: the sonic boom. As an airplane continually races forward and passes through the sound waves emitted by its engine, the waves begin to overlap in an expand-ing cone moving away from and behind the plane, particularly in the downward direction where air

is denser. The amplitudes of overlapping waves add together, and for sound waves amplitude translates into volume. Thus, the cone of overlapping sound waves sounds like an enormous boom as the shock wave strikes the ears of people beneath the flying plane.

Mini-Lab – Shock wave in Water

Materials needed:1. Large rectangular baking pan2. Water

Procedure:1. Set up pan and water as in the Doppler Effect Mini-Lab (on page 16), but now make each tap at or

slightly beyond the expanding waves.2. Observe the waves overlapping and hitting the walls to the sides of your path.

Sonic Boom

Pressure WavesIn Subsonic Flight

Shock Waveat Mach One

SupersonicShock Cone

Moving Source



Electromagnetic waves: RadarRadar is an acronym that stands for radio detection and ranging. The mechanism takes advantage of two properties of waves – reflection and the Doppler Effect. Regardless of whether they are mechanical (like sound or water waves) or electromagnetic (like radio, light, or microwaves), all waves reflect off surfaces with an angle of reflection that is equal to the angle of incidence across a “normal line” which extends perpendicularly from the surface of reflection.

Mini-Lab – Wave reflection

Materials needed:1. Aluminum foil2. Tape3. Flat table4. Two books5. Narrow-beam flashlight or laser pointer6. Two shipping tubes7. Protractor

Procedure:1. Tape aluminum foil to the face of one book with the shiny side facing outward. Secure that book in a

vertical position at one end of the table.2. Lay one shipping tube on the table pointed at an angle to the book, leaving an inch between the end of

the tube and the book. Tape the tube to the table.3. Measure the angle that the tube makes with the face of the book’s normal line.4. Lay the other shipping tube on the table facing the same point on the aluminum foil at which the first

tube is aimed but at a different angle.5. Stand the second book vertically behind the other end of the second tube.6. Point the flashlight or laser pointer through the first tube toward the foil. Move the second tube and the

second book until the light reflects directly through the second tube.7. Measure the angle that the second tube makes with the book’s normal line.

Radar works by sending a short pulse – often 0.0000016 sec or less – of electromagnetic waves in a particular direction and then “listening” for waves that are reflected back off a surface. Radio waves or microwaves instead of sound waves are used because of their high frequency, high speed,* greater longevity, and wider variety of available frequencies (to undermine detection). Usually, the wave pulses are frequency-modulated to increase reflection potential against a variety of sizes and textures of surfaces.

* Like other EM waves, radio waves travel near the speed of light – 292,792,458 m/s, or approximately 1000 ft/microsecond – even through a medium like air. Submarines and bats similarly use sound waves over shorter distances with their sonar mechanisms.

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Waves approaching along PO are reflected along OQ, where θi is the angle of incidence and θr is the angle of reflection.



EM waves: Radar (continued) and stealth

Depending upon size, shape, texture, and other factors about the reflecting surface and the wave-carrying medium, reflected wave energy usually is less than 1/10 of the energy emit-ted by the radar pulse. Thus, radar emitting devices must have supporting computers that accurately record direction, frequency, and speed of the sent radio waves. Receiving devices must be equally detailed and very sensitive; radar reception antennas typically are shaped like parabolic dishes to increase the number of captured return waves.

Additionally, a radar mechanism can calculate the speed of a moving object by account-ing for a Doppler shift created by waves reflecting off moving objects. When radar waves encounter a reflecting surface that is moving toward them, the waves are accelerated and compressed on the return by the speed of moving object. When a reflecting surface is mov-ing away, the radar waves are decelerated and rarefied (spread apart) on the return. The radar mechanism’s computer records the time that the waves take to return and then calcu-lates the velocity of the detected moving object.

Some modern airplanes use a variety of stealth modifications to minimize detection by radar and other devices. Interestingly, many stealth modifications are creative lower-tech ideas, including paint-color schemes that undermine visual detection, subsonic travel to preclude audio detection by sonic booms, and flawlessly smooth, flat hulls with sharp edges that simply reflect radar away from its emission source. Some stealth planes don’t even have tails. Far more sophisticated technological advances that enhance stealth capabilities include internalized engines whose heat generation and other input and output signatures are disguised by baffling devices, graphite-ferrite microspheres in surface paints that absorb electromagnetic energy, and layers of gold and indium foil on windows to prevent detection of distinguishable shapes inside the cockpit. Even the inner layers of stealth aircraft have geometries of varying angles and shapes to avert detection when frequency-modulated radar waves penetrate the outer hull. Ultimately, engineers know that no aircraft can be made totally invisible, but stealth aircraft sacrifice some structural stability and speed in favor of significant decreases in detectability.

Mini-Lab – Wave deflection* Note: The Wave Reflection and Deflection Mini-Labs also can be performed using

sound waves by replacing the light with a ticking timer, replacing the foil with a flat plate of steel and then with foam, and replacing the second book with a decibel meter.

Materials needed:Same as Wave Reflection Mini-Lab (on page 18)

Procedure:1. Repeat all steps of the Wave Reflection Mini-Lab (on page 18), but first crumple

the aluminum foil and leave it wrinkled before taping it to the book.2. Observe change in intensity and diffraction (scatter) of reflected light.

F117 “Nighthawk”

On November 10, 1988 the U.S. Air Force revealed the F-117A Stealth fi ghter to the public for the fi rst time. F-117A Nighthawk is the world’s fi rst operational air-craft completely designed around stealth technology. Flown only by the U.S. Air Force it was manufactured using radar-absorbent mate-rials and a radical new de-sign. The F-117A can evade radar detection, securing its place as the aerospace “tip of the spear” and serving to blind the enemy by destroy-ing command, control and radar early in any military campaign. About the size of an F-15C Eagle, the single-seat, twin-engine F-117A is powered by two non-af-terburning General Electric F404 turbofan engines, and has quadruple-redundant fl y-by-wire fl ight controls. In order to lower develop-ment costs, the avionics, fl y-by-wire systems, and other parts were derived from the F-16 Fighting Falcon, F/A-18 Hornet, and F-15E Strike Eagle. Among the penalties for stealth are 30% lower en-gine power, a very low wing aspect ration, and a high sweep angle needed to de-fl ect incoming radar waves to the sides.

Science In Flight Quiz



Quiz – Helicopters, engines, and waves

1. Which of the following is NOT true regarding helicopters?

a. Helicopters use Bernoulli’s Principle to achieve lift and control direction.

b. Helicopters have greater maneuverability than most other winged aircraft.

c. Helicopters can hover in air by creating an upward force equal to gravity.

d. The idea of the helicopter originated in the twentieth century.

2. At 0°C sound travels through dry air at approxi-mately 331.4 m/s. What is the speed of an airplane traveling at Mach 1.5?

a. 220.93 m/sb. 497.1 m/sc. 0.0045 m/sd. 332.9 m/s

3. Which of the following correctly explains how Newton’s Third Law of Motion affects the motion of a rocket?

a. The action of downward exhaust creates the reaction of upward thrust.

b. As the rocket passes the speed of sound, it cre-ates a sonic boom.

c. By expelling its fuel, the rocket becomes less dense and more buoyant.

d. As the speed of the rocket increases, decreased pressure above the nosecone pulls the rocket upward.

4. If you apply 50 N of force to a 2 kg ball, what will its acceleration be?

a. 100 m/s²b. 25 m/s²c. 0.04 m/s²d. 200 m/s²

5. According to the Doppler Effect, which of the fol-lowing will occur as an ambulance approaches you while its siren makes a constant noise?

a. You will hear the loudness of the siren increase.b. The driver will hear the pitch of the siren

increase.c. You will hear the pitch of the siren increase.d. You will hear a steady pitch and loudness from

the siren.

6. Which of the following is NOT true about radar?

a. Electromagnetic waves from radar travel at nearly the speed of light.

b. Most objects reflect less than 10% of the energy from radar waves that hit those objects.

c. Bats use radar to detect objects in or near their flight paths.

d. Stealth aircraft use both high-tech and low-tech modifications to minimize their detection by radar.



A debate of definition: FlightPenguins are called “flightless birds.” However, a penguin can control its overall densi-ty by holding or releasing air from its lungs, thus affecting its depth in water. The penguin uses muscles for thrust and for control over direction in water. So – regardless of conventional

definitions – do you think that what penguins do in water really is flight?

Scientists, like all people who employ language as a tool, must begin with an agreement about definitions of their terms. Read the following passage silently to prepare for a class-wide debate about the definition of “flight.”

Is movement through air required for flight? Many people describe the movement of spaceships on the way to the Moon or other planets as flight. Newscasters often say that the Space Shuttle, satellites, and the International Space Stations “fly high above Earth.” Yet all of those objects travel through airless space. Should we call what they are doing flying? If so, then isn’t penguins’ activ-ity under water really just another form of not-in-air flight? If not, then what should we call the activities of those spacecraft?

Is control of overall density or lift required for flight? Blimps and hot air balloons “fly” by floating, as helium and hot air both are less dense than the air in most of Earth’s atmosphere. So do blimps and hot air balloons fly? The overall densities in complex versions of these vessels might be controlled using such devices as sandbags or by releasing some of the lighter-than-air gas, but toy balloons don’t have such control mechanisms. So when a young child points into the air and says, “Mommy, my balloon is flying away,” is the child incorrect? You’ve probably seen a helium-filled balloon begin to fall after several days of pushing upward. Why does this occur, and does this slow-descent phenomenon change your mind about whether balloons fly?

Is control over direction required for flight? A balloon’s direction in air is determined by surrounding winds. So does that lack of control mean that helium-filled toy bal-loons don’t fly? And if a balloon does control its direc-tion (like a fan-directed zeppelin or hot-air balloon), does that mean that the balloon is flying? Also, what if directional control is pre-programmed or provided

from a remote loca-tion? Finally, if you decide that control over direction isn’t required for action to be considered flight, then do algae fly in water?

Written assignment – Definition of “flight”

Write a thorough definition of “flight,” limited to no more than a page. Include issues of movement through air, control over density or lift, and control over direction in your answer. Defend each part of your defini-tion, and give relevant examples.

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ASA

Science In Flight Unit 7 - Test



Test – Science in Flight

1. Fluid A is blue and has a density of 4.1 g/cm³. Fluid B is red and has a density of 0.847 g/cm³. If both fluids are poured into a beaker with pure water and they don’t undergo a chemical reaction, what will happen to them? Why?

2. An object placed into a tub displaces 3.45 lbs. of water while floating. How much buoyant force is acting on the object? Name the applicable prin-ciple.

3. Steel is denser than water. So how does a steel ship float on water?

4. Explain how thrust, drag, gravity, and lift affect airplane flight.

5. An undertow is created in the ocean when a fast-moving current of water runs parallel to the shore several feet below the surface. Use Bernoulli’s Principle to explain how an undertow can be dan-gerous to people swimming in the area above the undertow current.

6. What are the two major advantages of helicopters compared to most winged aircraft?

7. Define the term “jet engine,” and list two types of jet engines.

8. Explain how Newton’s Third Law of Motion and Newton’s Second Law of Motion both are used in rocket flight.

9. Why does a racecar driver hear a steady pitch from his engine while a spectator hears a rising then fall-ing set of pitches as the racecar passes?

10. At 0°C sound travels through dry air at approxi-mately 331.4 m/s. Calculate the speed of an air-plane traveling at Mach 2.7.

11. Explain how radar works to detect the location and velocity of moving objects.

12. List one low-tech modification and one high-tech modification that can be used to enhance an aircraft’s stealth capabilities.

Use a separate sheet of paper for any answers, as needed, and attach to test before turning it in.

density - palo verde high school afjrotc...density of the surrounding fluid and the overall...

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