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Wednesday, September 23 Dr. Rick Chappell
How Do We Get To SPACE, and How Do Rockets Work?
[REMEMBER: Students should prepare questions to ask Dr. Chappell
during the videoconference.]
Overview: This lesson involves a brief history of rockets and continues with Newton's Laws of Motion. The culminating activity is the building and launching of 2- liter bottle rockets where students use formulas and charts to measure height and velocity.
Students will use scientific process skills to accomplish this project that requires them to plan, design, examine and learn about motion and forces. This is a small group project. Each group of 4 students will design, build, test, launch and refine both a balloon rocket and then a 2-liter bottle rocket. As students prepare for launch, they will predict how much fuel (water) should be used in the 2-liter bottle rocket to provide the maximum performance. After the launch, students will evaluate their rocket's performance. Learning from their first launch, students will adjust the fuel load to improve their rocket's performance.
Students will sign up for launch day by completing a spreadsheet that has listed the amount of water, nose weight, total weight, and description and number of fins. During launch, students will time the flight from lift off until it touches down. Students will then use a formula to calculate the height and velocity and enter the data on the spreadsheet to make a double graph. H=(t/2)² x 16 V= t/2, H/V, x .68 = mph
Why: This lesson is a cross curriculum lesson design to excite students and give a real world example of why all curriculum areas are important in a project. They will be motivated to use their math and science skills. Students will see a practical application for classroom lessons. This lesson promotes social skills as students work in teams.
Concepts Taught: History, Physics, Graphs, Formulas
INTRODUCTION:
The wonder of Newton's Laws is obvious. On board an orbiting spaceship, the absence of gravity has thrilled our imaginations since the age of Jules Verne. In Jules Verne's 1860's work, From the Earth to the Moon, Jules Verne speculates about the weightlessness of passengers in route to the moon. The amazement comes from the apparent absence of gravitational attraction. Though Newton includes the behavior of gravity among his laws of inertia and motion, the absence of that pulling force seems magical to those who first experience it while orbiting the earth.
This lesson can be used to prepare students for any of the videoconferences offered in the“Space: Out of This World” series from Vanderbilt Virtual School. Students will learn about how rockets and space shuttles can escape Earth's gravity and orbit the Earth.
What impact do Newton's Laws have on astronauts, and how might they be demonstrated?
Objectives:
1. The students will be able to construct their own rockets.
2. The students will be able to identify and understand how Newton's 3 laws of motions are the basis of modern rocketry through teacher demonstrations and student experiments.
4. Students will use the internet to embellish their learning experiences.
5. Students will work in teams and as individuals during periods of hands-on activities to enhance
two-tier learning levels on an individual level and in a cooperative learning level.
6. Students will use scientific method to test their ideas about rocketry.
7. Students will find the center of mass and center of pressure on a rocket.
8. Students will create a scale drawing of their rocket.
9. Students will design and launch a stable rocket.
BACKGROUND:
I. History
A. 1200's AD - Used in the Middle East. Called "Chinese Fire Arrows"
1. Made of tubes stuffed with gun powder that when ignited, exploded and produced hot gasses that pushed the rockets into flight.
B. 1687, Sir Isaac Newton published a book of principles which have become known as Newton's Laws of Motion
C. Only since the 1700's, have rocket experimenters actually understood the scientific principles behind the motion of rockets.
D. Rockets were used in the War of 1812, which inspired the Star Spangled Banner.
II. Newton's Laws
A. First Law
1. Objects at rest will stay at rest, or objects in motion will stay in motion, unless acted upon by an unbalanced force.
B. Second Law
1. The acceleration of an object is directly related to the force exerted on that object and oppositely related to the mass of that object.
C. Third Law
1. For every action there is always an opposite and equal reaction.
III. Rocket Launch
A. For a rocket to lift off, force must be exerted. (First law)
B. The rate (speed) will be determined by two things: (Second law)
1. The mass (weight) of the rocket
2. By the force produced by the fuel.
C. The reaction, or motion, of the rocket away from the launch pad is equal to and opposite from the thrust of the engine or nozzle. (Third Law)
IV. What to do at rocket launch time?
- As each group is ready to launch, have one person from the team present the rocket and give a “briefing” on its design.
- The team must select the amount of water to place into the rocket and they are to record this data. Never fill the rocket more than ½ full of water.
- After the launch, each group should record all data about the flight
- After the entire class has launched their rockets, compile data on the rocket launch from the entire class.
V. Here are some ideas that to involve the class in discussion.
- How does the amount of water in the bottle affect the flight of the rocket? This data could be placed in an Excel spreadsheet and then graphed to allow students the chance to view performances based on water used.
- What rocket design worked better? Did the number of fins impact the flight. What about the size of the fins?
- Did you use difference size bottles? If so, how did the size of the bottle impact flight?
- Will a bottle with no nosecone or fins fly or be stable when launched?
VI. Possible Questions students might ask Rick Chappell, former NASA scientist and astronaut, in the videoconference about rockets.
A. Do rockets really fly?
B. If rocket engines burn oxygen, how do they work in space?
C. Why do rocket engines have nozzles?
D. Why are rockets so long?
E. If rockets don't fly, why do they have fins?
F. Why are rockets so stream-lined?
G. If rockets fly in space without interference from air or gravity, why must they still be balanced?
H. What caused the rocket to fly?
I. What caused the rocket to slow down and then return to earth?
J. Why did my rocket flip, tumble, and/or spin?
K. Why did some rockets fly higher than others?
VII. Answers.
A. Rockets move without the need of atmosphere (air).
B. Rockets carry oxygen with them as part of their propellant (solid fuel).
C. The purpose is to increase and direct the acceleration of gases as they leave.
D. To control the rocket and give it a control system.
E. Rockets are stabilized by the effects of air moving over the fins which function as controls.
F. Friction from the Atmosphere (air) will slow the rocket down while it is moving, called drag and turbulence.
G. In order for a rocket to remain stable (balanced), the center of pressure and center of gravity should be no closer than 1/2 the distance equal to the largest diameter of the body.
H. Newton's' third law of motion helps explain why the rocket flew. For every action, there is an equal and opposite reaction. The action that occurred was pressure escaping through the end of the bottle rocket. This cause the rocket to move in the opposite direction.
I. Friction caused by air against the rocket caused it to slow down… gravity caused it to return to the ground.
J. Some possible factors are:
- Unbalanced: When the rocket was built, it should have been top heavy. Adding weight to the nosecone area of the rocket helps it to fly straight when launched. The Center of Mass should have been close to the nosecone above the center of pressure when the stability test was performed prior to launch. If the center of pressure was close to or above the center of mass, it will cause the rocket to spin around its center of mass.
- Poor design: Did the nosecone stay on? Was the nosecone aerodynamic? What about the fins? Were the fins too small?
K. Some possible reasons are:
- Weight and fuel ratio: Weight of the rocket? Amount of water used? Amount of PSI?
- Was the rocket aerodynamic?
- Weather factors such as wind.
Pre-Activity: Balloon Rockets
Description: This activity is a simple science experiment that students can use to understand Newton's complex theory of Action and Reaction.
Background Information: This activity can be used with students at all ability levels. This lesson teaches students the simple laws of action and reaction. Using balloons and string, students will work in groups to create simple rockets. The whole class will then come together as a large group to conduct rocket races.
Materials:
- balloons
- string
- straws
- tape
- markers
- scissors
Procedure: (Be sure that all groups have the same size balloons.)
- Divide students into groups of 3-4. Students will work together to construct their rockets (see Internet websites listed for information on how to construct the balloon rockets).
- The students will experiment with their rockets. Students will blow up their balloons to various sizes and observe how far their rockets travel.
- Students will record their various measurements.
- Students will then be able to determine that the amount of air in the balloon is relevant to the distance that the rocket travels.
- Students will then record all observations regarding their rockets.
- Students will then come together as a large group.
- The class rocket races will take place.
Assessment: Students will be able to relate their observations to those of Newton's Law of Action and Reaction. Students will brainstorm ideas for other ways to demonstrate the concepts of Newton's Laws.
Internet Sites:
* http://www.creative-chemistry.org.uk/activities/balloons.htm
*http://www.amnh.org/mars/balloon.html
* http://unmuseum.mus.pa.us/exjet.htm
POST -ACTIVITIES
“Demonstrating Newton's Laws with a 2-Liter Bottle Rocket”
Materials needed: 2- liter plastic bottles; poster board; cardboard; construction paper; string; straws; Markers; rulers; scissors; pencils; glue and glue guns; duct tape; masking tape; plastic sandwich bags; modeling clay; water; rocket launchers. [Students can even bring in their own materials].
Rocket Launchers can be made or purchased. Several different science supply companies make launcher kits:
http://www.arborsci.com/Products_pages/cool_tools/cooltoolsbuy2.htm
http://sciencekit.com/category.asp_Q_c_E_594395
A. Building a Bottle Rocket
Bottle rockets are very easy to build. Make sure to test your rocket for the Center of Mass and Center of Pressure after you build your rocket.
1. Wrap and glue or tape a tube of poster board around the bottle.
2. Cut out several fins of any shape and glue them to the tube.
3. Form a nosecone and hold it together with tape or glue.
4. Press a ball of modeling clay into the top of the nosecone or try to press and tie it to the top of the bottle
or a little of both.
5. Glue or tape nosecone to upper end of bottle.
6. Decorate the rocket.
B. DISCUSSION about Rocket Stability
Key terms:
- Stable
- Unstable
- Center of pressure
- Center of mass
A rocket that tracks true (flies straight) through the sky is said to be a stable rocket. A rocket that veers off course or tumbles is said to be unstable. The difference between the flights of the stable and unstable depends upon its design. All rockets have two distinct “centers”. The first is the center of mass. This is the point about which the rocket balances. If you could set your rocket on the edge of a ruler, the center of mass is the point that the rocket would balance horizontally like a seesaw. (It is also the place in which half the mass is in front of the rocket and the other half is behind.) If a rocket is unstable, the rocket will spend around this center.
The other center in a rocket is the center of pressure. This is a point where half of the surface area of a rocket is on one side and the half is on the other. The center of pressure differs from center of mass in that its location is not affected by the placement of payloads in the rocket. This is just a point based on the surface of the rocket, not what is inside. During flight, the pressure of air rushing past the rocket will balance half on one side of this point and half on the other. You can determine the center of pressure by cutting out an exact silhouette of the rocket from cardboard and balancing it on a ruler edge.
The positioning of the center of mass and the center of pressure on a rocket is critical to its stability. The center of mass should be towards the rocket's nose and the center of pressure should be towards the rocket's tail for the rocket to fly straight. That is due to the lower end of the rocket (starting with the center of mass and going downward) has more surface area that the upper end. When the rocket flies, more air pressure exists on the lower end of the rocket than on the upper end. Air pressure will keep the lower end down and the upper end up. If the center of mass and the center of pressure are the same place, neither end of the rocket will point upward. The rocket will be unstable and tumble. So, to have a stable rocket, the center of mass must be in front of the center of pressure.
C. How to Determine the Stability of your Rocket
1. Tie a string around the middle of your rocket. Tie a second string to the first string or leave a very long “tail” (3 – 4 feet) on the string you used to tie around the rocket. Slide the string loop to a position where the rocket balances. Note: You might have to tie the nose cone in place to keep to from falling off.
2. Mark on your rocket where the loop is. This represents your Center of Mass.
3. Draw a straight line across the scale diagram of the rocket you made earlier to show where the ruler's position is. Label this line as the Center of Mass.
4. Lay your rocket on a piece of cardboard. Carefully trace the rocket on the cardboard and cut it out.
5. Lay the cardboard silhouette you just cut out on the ruler and balance it.
6. Draw a straight line across the diagram of the rocket. This line represents the Center of Pressure.
If your Center of Mass is in front of the Center of Pressure, your rocket should be stable. Proceed to the swing test. If the two centers are on top of each other or very close, add more clay to the nosecone. This will move the mass forward. Repeat steps 1 and 2. Check the new location of Center of Mass against the Center of Pressure.
D. Swing Test
1. Tape the string loop you tied around your rocket in the previous set of instructions so that it does not slip.
2. While standing in an open place, slowly begin swinging your rocket in a circle. If the rocket points in the direction you are swinging it, the rocket is stable. If not, add more clay to the rocket nose cone or add larger fins. Repeat the test until the rocket flies true in the direction you swing it.
NATIONAL STANDARDS
• Subject : Science
• Strand : Energy
• Standard SC.B.2.3: The student understands the interaction of matter and energy.
• Performance Benchmarks 1: knows that most events in the universe (e.g., weather changes, moving cars, and the transfer of a nervous impulse in the human body) involve some form of energy transfer and that these changes almost always increase the total disorder of the system and its surroundings, reducing the amount of useful energy.
Grade Level Expectation 1: understands that energy moves through systems.
• Strand : Force and Motion
• Standard SC.C.1.3: The student understands that types of motion may be described, measured, and predicted.
• Performance Benchmarks 1: knows that the motion of an object can be described by its position, direction of motion, and speed.
Grade Level Expectation 1: knows that a change in motion and position can be measured.
• Standard SC.C.2.3: The student understands that the types of force that act on an object and the effect of that force can be described, measured, and predicted.
• Performance Benchmarks 3: knows that if more than one force acts on an object, then the forces can reinforce or cancel each other, depending on their direction and magnitude.
Grade Level Expectation 1: recognizes the result of several forces acting on an object.
Grade Level Expectation 2: knows that the net force is dependent on the direction and magnitude of forces acting on a body.
• Performance Benchmarks 5: understands that an object in motion will continue at a constant speed and in a straight line until acted upon by a force and that an object at rest will remain at rest until acted upon by a force.
Grade Level Expectation 1: knows that an object at rest will stay at rest unless acted upon by an outside force.
Grade Level Expectation 2: knows objects in motion will remain in motion unless acted upon by an outside force.
• Performance Benchmarks 7: knows that gravity is a universal force that every mass exerts on every other mass.
Grade Level Expectation 1: knows that gravity is a force that causes an object to fall to the ground.
Grade Level Expectation 2: knows that gravity causes an object to have weight.
• Strand : The Nature of Science
• Standard SC.H.1.3: The student uses the scientific processes and habits of mind to solve problems.
• Performance Benchmarks 2: knows that the study of the events that led scientists to discoveries can provide information about the inquiry process and its effects.
Grade Level Expectation 1: uses systematic, scientific processes to develop and test hypotheses.
Grade Level Expectation 2: knows that the scientific method is a process that involves a logical and empirical but flexible approach to problem solving.
• Standard SC.H.2.3: The student understands that most natural events occur in comprehensible, consistent patterns.
• Performance Benchmarks 1: recognizes that patterns exist within and across systems.
Grade Level Expectation 1: knows that most natural events occur in patterns
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