Physics for Standard 9

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™ Physics and Model Rockets A Teacher’s Guide and Curriculum for Grades 8-11 Developed by Sylvia Nolte, Ed. D. Edited by Thomas E. Beach, Ph. D., Tim Van Milligan, A.E. and Ann Grimm EstesEducator.com ® educatorestesrockets.com 800.820.0202 © 2012 Estes-Cox Corp.INTRODUCTION Rocketry is an excellent means of teaching the scientific concepts of aerodynamics and Newton’s Laws of Motion. It integrates well with math in calculating formulas, problem solving and determining altitude and speed. In constructing a model rocket, the student must follow directions, read and follow a diagram and use careful craftsmanship. This unit on rocketry contains a student book, a series of Launch Log pages related to a lesson and math extension activities. The objectives for each lesson are stated, along with a list of the vocabulary to be emphasized, the materials needed and a strategy for each lesson. This guide is directed for teachers of eighth through eleventh grade whose students may have had some experience with the scientific concepts involved with rockets. Flexibility is built in through the use of the Launch Log pages and the math extension pages. A teacher can chose which ones to use or not to use. This guide integrates the content areas of science, math and English. Much of the work is done in small groups. This curriculum provides an enhancement to the study of space, space exploration or the study of motion. GOAL • Bring the concepts presented in physics to life through the experience of building and launching a model rocket. STUDENT OUTCOMES • Describe the four forces operating on any object moving through air and discuss their application to the flight sequence of a model rocket. • Describe Newton’s three laws of motion and how they relate to model rocketry. • Identify each part of a rocket and describe its function in relation to the four forces operating on any object moving through the air. • Design, assemble and launch a model rocket which is finished so that it is aerodynamically stable, produces a minimum of drag, maximum momentum and uses an appropriate recovery system. • Recognize and demonstrate skill in using mathematical formulas to determine altitude and speed. • Recognize the ways energy is transformed in a model rocket flight sequence. • Demonstrate proper safety procedures based on the Model Rocketry Safety Code when launching a rocket. ESTES 3 EDUCATOR™CONCEPTS TO BE DEVELOPED • How a rocket is constructed so that it is stable, has minimum drag and maximum momentum. • How the studies of physics and rocketry are related, specifically Newton’s three laws of motion, the four forces that operate on objects moving through air and how energy is formed. • How mathematical formulas are used to determine altitude, speed and velocity. SCIENCE PROCESS SKILLS • Observing • Reading and following a diagram • Analysis • Predicting • Describing • Evaluating • Problem solving GENERAL BACKGROUND FOR THE TEACHER There are four basic forces operating on any object moving through air. They are lift, drag, gravity and thrust. Lift is the force that is created when air moving over the top of an object, such as a kite or an airplane wing, moves faster than the air moving beneath it. There is less force (air pressure) against the top than beneath the object. This creates a force which lifts the object. It is generated by relative wind. Drag is the friction force experienced by any object moving through air as the air slides or drags past it. More drag is created by a larger surface, a rougher surface or by increasing speed. Drag can be minimized when constructing a model rocket but it can not be eliminated. Drag and gravity limit the height a model rocket can reach. An aerodynamically “clean” design (streamlined) and smooth surfaces can help minimize drag. Gravity is the force that pulls down upon any object near the surface of the earth. It acts through the center of gravity of any object. The amount of this force is proportional to the mass of the object and is inversely proportional to the square of the distance between the object and the Earth’s center. Thrust is the forward force exerted on a flying body. It is produced by the engine of a model rocket. Gravity must be overcome for the model rocket to rise vertically, so thrust has to be greater than the weight in order for the rocket to lift off. Aerodynamics is the study of the motion of air and the relative motion between air and objects in the air. An important concept in the study of aerodynamics is relative wind, which is the motion of air in relation to an object. One example is a kite being held stationary in a ten mph breeze vs. one being pulled at ten mph in through stationary air. Both see the same relative wind. ESTES 4 EDUCATOR™The center of gravity refers to the point in a rocket around which its weight is evenly balanced. The center of pressure refers to the point in a rocket where all external aerodynamic forces acting on a complete rocket, including the fins, is centered. Model rockets rely on aerodynamics to fly properly just as butterflies and airplanes do. The flight performance of any model rocket is the result of the combined effects of the four basic forces acting upon it. The phases of flight of a model rocket demonstrate these forces: When the engine is ignited, thrust is generated which exceeds the force of gravity. This unbalanced force accelerates the rocket upwards, building velocity either until engine burnout or until drag forces are sufficient to equal the unbalanced thrust force (terminal velocity). At engine burnout, gravity and drag work to slow the rocket down. When all upwards (vertical) velocity is lost, gravity causes the rocket to accelerate downwards, building velocity until either the recovery system deploys, terminal velocity is reached or the rocket impacts the ground. The recovery system is designed to employ drag and/or lift to oppose the force of gravity, allowing a controlled descent and safe landing. According to Bernoulli’s Principle, the faster a fluid moves the lower the lateral pres- sure it exerts. By causing air to move faster over certain surfaces of a rocket, i.e. fins or wings, air pressure may be reduced on those surfaces creating lift. The fins enable the rocket to correct its flight when it is deflected. When air moves over the “top” of the deflected fin, the air travels faster than the air under the fin. This creates lift. The lift force, generated by relative wind, causes a stable rocket to correct itself by rotating around the center of gravity until it is flying straight again. Weathercocking is a phenomenon that occurs when a rocket is launched in a crosswind. The crosswind creates a relative wind that is at an angle to the path of the rocket, generating lift on the fin surfaces that causes the rocket to tip in the direction of the crosswind. A rocket weathercocks because it is stable. Drag increases as the square of the velocity of the rocket increases. A high thrust engine will cause a rocket to experience much more drag than a low thrust engine due to higher velocities achieved. Newton’s three laws of motion are involved in the launch and flight of model rockets. The laws are as follows: 1. A body at rest will remain at rest and a body in motion will continue in motion with a constant speed in straight line so long as no unbalanced force acts upon it. This law is referred to as the law of inertia. 2. If an unbalanced force acts on a body, the body will be accelerated; the magnitude of the acceleration is proportional to the magnitude of the unbalanced force, and the direc- tion of the acceleration is in the direction of the unbalanced force. ESTES 5 EDUCATOR™3. Whenever one body exerts a force on another body, the second body exerts a force equal in magnitude and opposite in direction to the first body. This law relates to the principle of action - reaction. Energy is neither created nor destroyed. It is transformed. During a rocket flight, chemi- cal energy is transformed into mechanical energy, heat, light and sound energy. In a model rocket, light and sound energy are very small and may be ignored. Part of the mechanical energy is transformed to the kinetic energy of the rocket’s motion. Part of the mechanical energy is transformed into heat energy by friction of the rocket moving through the air. Part of the mechanical energy is transformed into kinetic energy of indi- vidual air molecules as they are deflected by the rocket (drag and lift). Part of the kinet- ic energy is transformed into the potential energy of the rocket as it rises higher and higher. Part of the stored chemical energy is released as waste heat energy during com- bustion. ESTES 6 EDUCATOR™UNIT PLAN Lesson 1 (One Day) AERODYNAMIC FORCES : WHAT THEY ARE AND WHAT THEY DO Objectives of the Lesson: The student will be able to : • Recognize the four basic forces operating on any object moving through air. • Describe and demonstrate the effects of relative wind and lift on objects moving through air. • Describe and demonstrate the effects of drag and gravity on objects on objects moving through air. • Describe and compare friction drag and pressure drag. • Recognize and use vocabulary related to rocket flight. • Record experiences and ideas in student journal. BACKGROUND FOR THE TEACHER The understanding of the basic forces of motion, lift, drag, gravity and thrust, is essential for students who will be constructing and launching rockets. All of the forces are interacting during a rocket flight sequence. The information in the “Student Book” will help teachers and students with their understanding and their application to model rockets. VOCABULARY Lift: the force that occurs when air moving over the top of a moving object travels faster than the air under it and uneven pressures are pro- duced according to Bernoulli’s Law. Thrust: the forward force on a flying body which, in the case of a rock- et, has to be greater than the force of gravity in order for lift-off to occur. Gravity: the force that pulls down on any object near the surface of the earth. Drag: the resistance or friction force experienced by any object moving through air or air moving over a non-moving object. Relative wind: the motion of air in relation to an object. Lift is generat- ed at a right angle to relative wind. Angle of attack: the angle between the relative wind direction and an imaginary line through the center of a flying surface such as an airplane wing or a rocket fin. Generally, as the angle of attack increases (raising the forward edge of the surface), so does lift and drag. Velocity: the rate of motion or speed in a given direction. Measured in terms of distance moved per unit time, in a specific direction. Viscosity: measures the resistance to motion of a fluid moving over a surface. ESTES 7 EDUCATOR™VOCABULARY (Continued) Pressure drag: the force that retards the motion of a moving object caused by an unbalance of pressure. Friction drag: the retarding force produced by an object sliding past the molecules of the fluid it is moving through. The amount of friction depends upon the amount of surface, the roughness of the surface, the den- sity of the fluid, the viscosity of the fluid and the characteristics of the flow (laminar or turbulent). Laminar flow: smooth steady air flow parallel to the surface of a moving body, usually found at the front of a smooth body moving in relation to the air around it. Turbulent flow: air movement that is uneven over the surface of a moving body; the air movement is not smooth, usually around an uneven surface. STRATEGY Materials needed for each student : A copy of the “Student Book”, a strip of paper, 1” x 12”; a copy of Launch Log 1; and a model rocket kit. Students should have a manilla envelope or folder for the materials and journal sheets that will be accumulated during this unit. Motivation: Show the students a model rocket that has already been constructed. Allow the students to discuss what a rocket is used for today and what it was used for in the past. Ask the students what they think has to happen to get a rocket off the ground and into space. Ask the students to discuss the construction of the rocket and guess or predict why it has the shape and parts that it does. Introduce the “Student Book” by asking students to predict some of the scientific principles that might be in this book. A. Distribute Launch Log 1. The students should complete the first two sections before they begin reading the booklet. B. Allow the students to read the section, Lift, with a partner or in a small group. C. Each student can demonstrate lift individually. Give each student a strip of limp paper, such as newspaper, an inch wide by twelve inches long. They should hold the paper with the thumb so the paper is just draping over the index finger with the long part away from them. Hold the index finger near the mouth and blow gently over the index finger. ESTES 8 EDUCATOR™D. Before the students begin reading the section, Drag, ask them to rub their index finger across the surface of the desk. Ask them to increase the speed. Ask them to describe what they begin to notice about their finger as they do this. (They should feel heat.) Ask them to rub hard rather than fast. Ask the students if they know what they are experiencing (friction). Friction and drag are related concepts. Allow the students to read the section on drag. E. Before the students begin reading the section, Gravity, ask them to look at their student book as it rests on the desk. Two forces are acting on the book. Ask if they know which ones. The force of gravity is pulling the book downward and the desk is pushing against it holding it up. Ask the students to pick the book up and let it rest on their hand. What forces are acting on the book now? Let the book drop onto the desk. What forces are acting on the book as it dropped? Closure: Briefly review the concepts, using the vocabulary at the bottom of Launch Log 1. Evaluation: Observe student participation and questions. Review their work on Launch Log 1. NOTES ESTES 9 EDUCATOR™Chapter One AERODYNAMIC FORCES: What They Are and What They Do Aerodynamics Aerodynamics is the study of the motion of the air and the relative motion between air and objects in No angle of attack the air. Model rockets rely on aerodynamics to fly Small lift force properly, just as butterflies, kites and airplanes do. Small drag force The flight performance of any model rocket is the result of the combined effects of aerodynamics and other forces acting upon it. High angle of attack Large lift force The four basic forces on flying objects, such as a Large drag force model rocket, are lift, drag, gravity and thrust. Aerodynamic forces are the forces generated as a result of the motion of an object through the air. Excessive angle of Therefore, lift and drag are aerodynamic forces. attack and stall Thrust can be generated by aerodynamic forces, Very small or zero such as a propeller, but is not inherently aerody- lift force namic in nature. Very large drag force Lift The faster a fluid moves, the lower the lateral pres- Drag sure it exerts. By causing air to move faster over Drag is the force experienced by any object mov- certain surfaces of an object, air pressure is reduced ing through a fluid, such as air or water, that which creates lift. This law is known as opposes the motion of the object. It is the resist- Bernoulli’s Principle. A kite, for example, is pushed ance caused by the motion of water or air as it up when the air moving over the kite moves faster drags past the object or is pushed out of the way. than the air moving beneath the kite. There is less Drag increases the larger or rougher the surface, force against the top of the kite than beneath it. the thicker the fluid or the faster the object is mov- The force which is created pushes the kite up and ing. is called lift. Drag can also be increased by a difference in pres- sure between the front and rear of the object. While lift can be a favorable aerodynamic force, drag can be an unfavorable force. Drag and gravity limit the height a model rocket can reach. Drag can be understood by thinking about what is expe- rienced when you pass your hand through a bathtub of water. As described above, water is a fluid with many of the same drag characteristics as air. Using your hand as a test “model rocket” and the Lift is generated by relative wind. Relative wind is bathtub of water as a “wind tunnel”, you can gain the motion in air in relation to an object, such as a an intuitive idea for how air resists the motion of a kite in a breeze. It can also be created by running model rocket in flight. with a kite, if no wind is blowing. The angle of attack is the angel at which a wing or kite moves in relation to the relative air stream or “relative wind”. The greater the angle of attack of a wing, the further and faster the air must flow over the wing and the greater the lift force produced. However, when a flying object has too great an angle of attack, it will stall because the airflow becomes turbulent and detached from the object, no longer traveling along its surface. When an object stalls, the lift produced decreases drastically, most likely falling to zero. Drag is also increased greatly. ESTES 10 EDUCATOR™As you pass your hand under the surface of the Pressure drag is the retarding force caused by the water, you can vary the speed of your hand and feel imbalance of air pressures on a moving object. the varying resistance to motion (drag effect) of the Pressures on a moving object vary with the objects surrounding water. speed, direction of motion and its size and shape. The effect of the size of the surface can also be Friction drag is the retarding force produced by an experienced by changing the orientation or shape object sliding past the molecules of the fluid of your hand as you pass it through the water. through which it is moving. The amount of friction More drag will be experienced against the back of drag produced by the motion depends on the your hand than against the edge of your hand. amount of surface exposed to the motion of the Drag will also vary as the shape of your hand fluid, the roughness of the surface, the density of ranges from a fist to outstretched fingers. the fluid and the viscosity of the fluid. You can also experiment with different shaped Imagine a very sharp thin plate moving through the objects other than your hand. Place spheres, blocks air. It is moving at zero angle to the air stream and or streamlined shapes on sticks and pass them there is no unbalance of pressure forces. However, through the water. You should be able to feel the there is still drag because the air is rubbing on the difference in resistance to motion the water devel- surface. This friction drag is confined to a thin ops for each shape at a given speed. region close to the body surface. You have experienced drag when you have been riding a bicycle fast. You could feel air rushing past you and you could feel air pushing against you slowing you down. Viscosity measures the resistance to motion of a Two types of drag effect the flight of a model rock- fluid moving over the surface. Low-viscosity flu- et. They are pressure drag and friction drag. ids, such as air and water, flow easily. Substances When a baseball is sitting still on the ground, the which do not pour easily, such a motor oil or pressures all around it are the same. The atmos- molasses, have high viscosity. pheric pressure on all parts of the ball are equal. There is no drag because there is no unbalance of On the surface of the object the velocity is zero. pressure forces. If the ball is thrown or hit by a bat Just off the surface, the air speed increases with the air around the ball starts to move. The pres- height above the object to a maximum speed called sures around it change and a pressure imbalance is the free-stream velocity. This is the speed at which created. This is called pressure drag. the object is moving through the air. The thin region at where the air speed changes is called the bound- Drag is demonstrated as the ball slows down after ary layer. Within the boundary layer, the effects of it is thrown or hit. 95% of the drag on a sphere viscosity are dominant and cause friction drag. comes from pressure drag. Viscosity is a factor in both friction and pressure drag. In friction drag, viscosity acts directly to pro- duce shearing stresses in the boundary layer. For pressure drag, viscosity riggers a flow “separation” from the body. Separation is the behavior of the flow when the air does not follow the body contour of an object, but breaks away into a turbulent wake. This separation of the airflow is a reason for the pressure unbalance which causes pressure drag on aerodynamic shapes, such as model rockets. The two figures show the difference in flow about a circular cylinder with a large wake and the flow about a streamlined shape with a small wake. The figures show that the streamlined shape is designed to reduce the amount of flow separation. The size of the wake is reduced. Drag is reduced because the flow attached to the body allows the pressure to build back up to levels near the pressure of the nose. This reduces the pressure unbalance and cuts drag. ESTES 11 EDUCATOR™Drag increases as velocity or speed increases. The drag experienced by the object directly varies with To prevent flows from separating, it is essential to the square of the velocity of the moving object. use aerodynamic shapes that are rounded gently The basic drag formula for the effect of velocity on and never have any sharp changes in direction. drag is: 2 When there are sharp changes, the viscosity of the D = C x A x 1/2 ρ x V D air makes the flow resist these changes in direc- C is the “coefficient of drag” which depends on D tions and forces the flow to break away. the shape and surface smoothness of the rocket. A is the cross sectional area of the rocket or the There are two patterns of flow, turbulent flow and frontal area of the rocket as seen from directly in laminar flow. Viscosity affects these flow patterns front of it. ρ is density of air through which the rocket is mov- in the air boundary layers moving over aerodynam- ing, symbolized by the Greek letter Rho (pro- ic shapes. nounced “row”). V is the velocity or speed of an object in relation to Laminar flow exists when the boundary layer of a 2 the wind. V means VxV, the velocity squared. fluid or air next to the surface is smooth and “attached” to the surface. The air acts as if it were As you can see, if the velocity of an object dou- in layers. The molecules in each layer slide over bles, the amount of drag is four times as great. If V the other molecules. The molecules in the layer or velocity tripled, the drag increases nine times. next to the surface have zero velocity. Each suc- ceeding layer further from the surface has a higher For a more detailed discussion of model rocket velocity of motion relative to the surface. Friction drag, see Estes publication, drag depends upon the rapidity with which the velocity changes. Aerodynamic Drag of Model Rockets. Gravity Gravity is the fore that pulls down on mass of any Turbulent flow exists when the boundary layer of object near the Earth through its center of gravity. fluid or air next to the surface is not smooth. The Gravity and drag limit the height a model rocket motion of the molecules is much less regular can reach. In general, light weight helps overcome because of the mixing of the different layers and gravity. The force of gravity varies inversely with the large fluctuations of velocity of the molecules the square of the distance between the center of at different distances from the surface. gravity of the object and the center of the Earth. An object, B, which is twice as far from the center of the earth as an object, A, will experience one fourth the gravitational attraction as object A. Because model rockets remain at nearly the same distance from the center of the Earth, gravity remains a near constant. Thrust Thrust is a forward propulsive force that moves an object. On an airplane, thrust is generated by the engines, propellers or exhaust. The flapping wings of a bird provides thrust for the bird. In a model rocket, thrust is produced by the rockets engines. Thrust must be greater than the weight of the rocket in order to overcome gravity and lift off from the earth. ESTES 12 EDUCATOR™Lesson 2 (One Day) NEWTON’S LAWS OF MOTION: HOW THEY GOVERN THE MOVEMENT OF OBJECTS Objectives of the Lesson: The students will be able to: • Recognize Newton’s Laws of Motion which govern the movement of all objects on Earth and in space. • Describe and demonstrate the effects of the three Laws of Motion on moving objects. • Recognize and use vocabulary related to rocket flight. • Record experiences and ideas in the journal. BACKGROUND FOR THE TEACHER Newton’s Laws of Motion help the student understand the scientific basis for how rockets work. The three laws relate the motion of objects on earth and in space. The laws govern what happens during a flight sequence. Chapter 2 in the “Student Book” explains the laws of motion and offers some practical examples of each one. VOCABULARY Rest: the state of an object when it is not changing position in relation to its immediate surroundings. Motion: the state of an object that is changing position in relation to its immediate surroundings. Unbalanced force: a net force in excess of any opposing force. An unbalanced force causes a change in a body’s inertia causing it to acceler- ate, according to Newton’s second law. Inertia: the tendency of a body at rest to remain at rest or a body in motion to remain in motion, unless pushed or pulled by an unbalanced force. Kinetic inertia: the tendency of a body in motion to continue in motion in a straight line at a constant speed. Static inertia: the tendency of a body at rest to remain at rest. Action/reaction: Newton’s Third Law of Motion. Mass: quantity or amount of matter an object has. Weight depends on mass. Acceleration: a change in velocity. Weight: the force that results from the Earth’s gravitational attraction on the mass of an object. An object’s weight is found by multiplying its mass times the acceleration due to gravity. ESTES 13 EDUCATOR™STRATEGY Materials needed for each student: A copy of the “Student Book”; Launch Logs 2 and and 3; and individual folders. Motivation: Show the students an uninflated balloon. Show them a completed model rocket. Ask them to describe any similarities between the two objects. Then inflate the balloon and either tie it closed or hold it so that the air is inside. Ask the students to describe why they think the balloon stays inflated. Ask them again to discuss any similarities between a rocket and a balloon now that the balloon is inflated. When they have had an opportunity to discuss it, draw the following diagram on the board: This diagram shows that air inside the balloon is compressed by the balloon’s rubber walls. The air pushes back so that the inward and outward pressing forces are balanced. Release the nozzle of the balloon. The air will escape and propel the balloon in a rocket flight. Allow the students to discuss what forces and laws are affecting the balloon’s erratic flight. A. Distribute Launch Log 2, “What I Think”. After the students have watched the bal- loon demonstration, allow them to complete Launch Log 2. Their answers are their own ideas and do not need to be correct, but will instead provide an opportunity to think about the concepts involved. B. Allow the students to read the section on Newton’s First Law of Motion in Chapter 2 with a partner or in a small group. ESTES 14 EDUCATOR™C. Each student can demonstrate this law. A book sitting on a desk is at rest. What kind of inertia is presented? (static inertia) What could cause the book to move according to Newton’s First Law? (an unbalanced force) Direct the students to apply an unbalanced force to the book to cause it to move. Allow each student to stack some books up to increase the mass and try to push with the same force. Observe what happens to the acceleration. What needs to happen to create acceleration equal to the acceleration of the first experiment? Ask the students to think about what occurs when a ball is tossed. Has anyone been able to throw a ball with such force that it continued in motion in a straight line? What unbalanced forces acted on the ball to keep it from continuing in motion in a straight line? D. Allow the students to read the section on Newton’s Third Law of Motion and to try the demonstration pushing the index finger against the desk. E. Ask the students to describe how the balloon demonstration was an illustration of Newton’s Third Law in Motion. (The unbalanced force on the inside front end of the balloon pushes the balloon around the room. The action of gas escaping from the bal- loon causes a reaction, the balloon moving forward.) F. Allow the students to complete the reading of Chapter 2 by reading the section on Newton’s Second Law of Motion. Give each small group a tennis ball or other small ball and allow them to observe the ball’s performance in relation to the second law of motion. Closure: Allow the students to complete Launch Log 3. Evaluation: Observe student participation in the demonstrations and discussion. Review their work on the Launch Log pages. NOTES ESTES 15 EDUCATOR™Chapter 2 THE LAWS OF MOTION How They Govern All Objects Newton’s Laws of Motion were described by Sir force of gravity is pulling the ball downward. Your Isaac Newton in 1687 in his book, Philiosphiae hand is pushing against the ball to hold it up. The Naturalis Principia Mathematica. These laws of forces acting on the ball are balanced. The tendency motion or principles govern the motion of all of the ball to remain at rest when no unbalanced objects, whether on Earth or in space. The laws of forces act on it is called static inertia. motion provide a scientific basis for understanding how rockets work. Newton’s First Law Objects at rest will stay at rest, and objects in motion will stay in motion in a straight line unless acted upon by an unbalanced force. This law is also referred to as the law of inertia. Inertia is the tendency of a body at rest to remain at rest unless pushed or pulled by an unbalanced force. A body in motion continues to move in the same direction at the same speed unless acted upon by an unbalanced force. Rest and motion can be thought of as opposite. Rest is the state of an object when it is not chang- ing position in relation to its surroundings. Motion means an object changing its position in relation to its surroundings. These are both relative terms. The important idea with these two words is in rela- tion to its surroundings. The ball changes from a state of rest, being acted upon by balanced forces to a state of motion, being acted upon by unbalanced forces when you let the As you are sitting in your chair, you can think of ball go or you move your hand upward. When an yourself as being at rest. What if your chair is a object is at rest, it takes an unbalanced force to seat on an airplane in flight? make it move. You would still be said to be at rest in relation to your immediate surroundings. The law also states that once an object is in motion, Rest, as a total absence of motion, does not exist in it will continue in motion in a straight line. It takes nature. Even as you are sitting in your chair, you an unbalanced force to stop it or change its direc- are still moving because your chair is sitting on the tion or speed. This is called kinetic inertia. surface of our moving planet that is orbiting the sun, which is moving through the universe. While you are at rest in relation to your immediate sur- roundings, you are traveling through space at hun- dred miles per second. Motion is defined as an object changing position in relation to its surroundings. Think of a ball sitting on the ground. It is at rest. When the ball is rolling, it is in motion, because it is changing position to its Motion in immediate surroundings. When a rocket blasts off the launch pad, it changes from a state of rest to a straight line at state of motion. constant speed Newton’s first law also involves the idea of unbal- If you threw a ball, what unbalanced forces prevent anced force. When you hold a ball in your hand it from staying in motion in a straight line forever? without moving it, the ball is at rest. As the ball is The forces of drag and gravity cause it to fall to held there, it is being acted upon by forces. The earth. ESTES 16 EDUCATOR™Newton’s Third Law Whenever one body exerts a force on another, Newton’s second law can be illustrated by drop- the second body exerts a force equal in magni- ping a small ball. The ball accelerates rapidly gain- tude and opposite in direction on the first body. ing speed as it falls from your hand. The ball falls or because of the unbalanced force of gravity acting For every action there is always an opposite and on it. The ball is accelerating positively as it falls- equal reaction. it is gaining momentum. Momentum is the product of mass times velocity. The mass or weight of the ball stays the same, but the speed or velocity Here is an illustration for the third law. A skate- changes. board and its rider are at a state of rest. They are not moving. The rider steps off the skateboard. Does this mean that a ball dropped from an air- This is called an action. The action causes the plane high in the sky would accelerate indefinitely? skateboard to travel a distance in the opposite It would not because of another force acting upon direction. The skateboard’s motion is called a reac- it. The ball is passing through the air. The air tion. resists the movement of the ball through it. The resistance is a force called drag. You can demonstrate Newton’s third law The ball is subject to acceleration toward the by gently pressing your index finger on your table ground because of gravity. It is prevented from or desk. Keep pushing, harder and harder. Do you accelerating indefinitely because of the drag of air. think the table is pushing back? Push even harder. The ball will eventually reach a speed where the If the table is not pushing back, why doesn’t your drag force is equal to the force of gravity on the finger go through the spot where you are pushing ball. This is called terminal velocity. When the ball with your finger? As you exert a force or action on reaches terminal velocity, there is no longer any the table, the table pushes back on your finger. The unbalanced force on the ball so it no longer accel- force you apply with your finger is the action. The erates and it falls at a constant speed. table’s resistance is the reaction. When you toss a ball up in the air, will it continue up indefinitely? As it leaves your hand, it achieves When the force applied is greater than the force a certain velocity and ceases to accelerate positive- with which the object can resist without motion, ly. This is the maximum velocity of the ball. As the part of the force being applied will produce motion. ball rises, its motion is resisted by drag, an unbal- When you apply more force with your finger than anced force, which slows the upward motion. This the force with which the table can react, the finger is called negative acceleration. The ball is also will dent or punch a hole in the table or the table being attracted toward the center of the earth by will move. Since every action always produces an gravity, an unbalanced force, which is acting on the equal reaction, an equal amount of force is present ball to slow it down. This force is also producing in both the action and reaction. negative acceleration. Newton’s Second Law These two forces acting on the ball slow it down If an unbalanced force acts on a body, the body and cause it to stop. At this moment the ball has will be accelerated; the magnitude of the accel- zero momentum because it has zero velocity. The eration is proportional to the magnitude of the force of gravity which produced the negative unbalanced force, and the direction of the accel- upward acceleration continues to act, producing a eration is in the direction of the unbalanced positive downward acceleration causing the ball to force. fall back to Earth with increasing speed. This is or resisted by the drag the ball encounters as it moves Force is equal to mass times acceleration. through the air. The drag force now acts upward, opposing gravity, because the ball is now falling downward through the air. The second law of motion is a statement of a math- ematical equation. The three parts of the equation are mass (m), acceleration (a) and force (F). The equation is written as follows : F= m x a An unbalanced force is one that is not matched or balanced by an opposing force. An acceleration is a change in velocity. Mass refers to quantity or the amount of matter an object has. ESTES 17 EDUCATOR™Lesson 3 (One Day) INTRODUCING MODEL ROCKETS - HOW THEY ARE CON- STRUCTED The Effects of Aerodynamic Forces Objectives of the Lesson: The student will be able to: • Identify the parts and functions of a model rocket. • Describe the phase of a model rocket flight and relate each phase to the aerodynamic forces at work. • Recognize and use the vocabulary related to rocket flight. • Demonstrate the ability to read and follow directions. BACKGROUND FOR THE TEACHER Before ordering rockets, determine who are the experienced rocket builders. They may need a more difficult kit. As the students begin to construct their rockets, there are some practical hints that will help them be more successful and help the construction go more smoothly. Each student should bring a small shoebox for storage of materials and for a place to keep the rocket when glue is drying. Plan each step of the construction carefully so that there is enough time for glue to dry, preferably over night. It works well to have any gluing steps take place at the end of the period. The rockets can then be stored or left to dry in the shoe box. It is important to circulate among the students as they are building their models so that the proper techniques are being followed and so that their model building is successful. Each student’s name should be written on a body tube light- ly in pencil. Do not use ink or ballpoint pen. Model rockets can be painted and decorated if there is time. VOCABULARY Nose cone: the foremost surface of a model rocket, generally tapered in shape for streamlining, it is usually made of balsa or lightweight plastic. Recovery system: a device incorporated into a model rocket for the purpose of returning it to the ground in a safe manner. Usually achieved by creating drag or lift to oppose the acceleration of gravity. All model rockets must employ a recovery system, such as a parachute. Body tube: a specially wound and treated cardboard or lightweight plastic cylinder used to make the fuselage or airframe of a model rocket. Launch lug: round, hollow tube which slips over the launch rod to guide the model during the first few feet of flight until sufficient airspeed is reached allowing the fins to operate. Fins: the stabilizing and guiding unit of a model rocket; an aerodynamic surface projecting from the rocket body for the purpose of giving the rocket directional stability. ESTES 18 EDUCATOR™VOCABULARY (Continued) Engine: (model rocket) a miniature non-metallic solid fuel rocket motor that contains propellant and may contain a delay element and an ejection charge. Designed to impart force to accelerate the rocket during flight and to activate the recovery system at or near apogee. Weathercock: to turn into the wind, away from a vertical path. Thrust phase: the period of time a during which the propellant is burning and the rocket motor is producing thrust. Coasting phase: the period of time immediately following propellant burnout and preceding the ignition of the ejection charge of the engine during which the rocket coasts upward on its momentum. Recovery phase: the period of time following the deployment of the recovery system which allows the rocket to drift easily back to earth. Apogee: the peak altitude of a model rocket. STRATEGY Materials needed for each student: Copies of the “Student Book”; copies of Launch Logs 4 and 5; a model rocket kit; a bottle of white or yellow construction glue; and a small shoe box with the student’s name on it. Some students who are more experienced rocketeers may be allowed to build a more complex model. Motivation: If possible, show the video tape, “Ignite the Imagination” by Estes Industries or other video showing rocket flight. Use Journal page 4 to accompany the video. The students will be looking for examples of the four aerodynamic forces acting on the rocket. They will also be looking for examples of Newton’s Laws of Motion during the flight sequence. They should make notes on the Journal pages as they watch the video. A. Discuss the video and the students’ responses to it on Launch Log 4. B. Go over pages 8 and 9 in the student book, the parts of a rocket and the flight sequence of a rocket. Allow the students to guess why each part is essential, what it is designed to do and why it has that specific shape or form. Emphasize the concepts of drag, gravity and thrust in particular. C. Distribute a model rocket to each student. Students should carefully examine the package noting the rockets length, diameter, recovery system and recommended engines and record these on Launch Log 5. Students should use the parts list on Launch Log 5 to find and identify each part. They may not be able to determine a purpose for each part at this time, but they should do as many as possible. The students should go over the assembly instructions either in a large group or in small groups to get a general overview of how the rocket will be constructed. Emphasize the importance of following the instructions exactly. This should also point out any problem areas. ESTES 19 EDUCATOR™D. The students should assemble the engine mount precisely as the directions indicate. When they have finished the engine mount, the glue should be allowed to dry overnight. Closure: If time allows, students can work in small groups to complete Launch Logs 4 and 5. Evaluation: Observe student work on the rockets for craftsmanship and following directions. Review their work on Launch Logs 4 and 5. NOTES ESTES 20 EDUCATOR™Chapter 3 MODEL ROCKETS Taking Aerodynamic Forces into Account Model Rocket Components D. Launch Lug The launch lug is attached to the air frame. It is a tube In Chapter 1, you studied the four forces of lift, that slips over the launch rod to guide the model dur- drag, thrust and gravity. In this chapter you will ing the fraction of a second after engine ignition until study the construction of model rockets to learn it reaches the speed necessary for the fins to control how these forces affect the flight sequence of the flight. The launch lug is a small tube shaped like a model rockets. soda straw. It is usually made of paper or plastic. All model rockets have the same basic components. E. Fins The diagram below shows a typical model rocket. Acts like the feathers on an arrow, guiding the rocket in a precise flight pattern and providing stability. Fins may be made of balsa, fiberboard, thin plywood or plastic. A. Nose Cone The front end of a rocket, which is usually shaped to minimize air resistance or drag. F. Engine The shock cord and parachute are often attached to Provides the power that causes the rocket to move. the nose cone. It is a pre-packaged solid propellant engine. B. Recovery System G. Engine Mount Assembly A recovery system slows a rockets descent, bringing Holds the engine in the proper position in the body the rocket safely back to Earth. The recovery system tube. can be a parachute, as in this diagram. A shock cord is attached which is anchored to the body tube of the Model Rocket Flight Sequence rocket. The shock cord absorbs much of the force of The diagram pictured illustrates the flight profile of a the deployment of the recovery system when the ejec- model rocket. As you trace the sequence, you can begin tion charge functions. There are several types of recov- to understand how the combined effects of the forces ery systems. They are stored in the rocket’s body dur- you read about in Chapter 1 act upon the rocket. ing the thrust and coast phases of the flight sequence. As the rocket is launched, thrust is provided by the C. Body Tube engine and overcomes the force of gravity. Thrust The body tube is the basic structure of the rocket to has to be greater than the weight in order for it to lift which other parts are attached. It is usually long off. Drag is another force acting on the rocket. Drag and slender. Most body tubes are made of paper and gravity limit the height a model rocket can reach. that is tightly wound in a spiral pattern. The tube is Drag can be minimized, but it cannot be eliminated. designed to be strong, but light. Other names for the body tube are the fuselage or the air frame. ESTES 21 EDUCATOR™