Rocket_Racer_s by yantingting

VIEWS: 9 PAGES: 9

									                                              Rockets Activity

                                              Rocket Races
                                              Objectives:
                                              Students investigate Newton’s Third Law of
                                              motion by designing and constructing rocket-
                                              powered racing cars.

                                              Description:
                                              Individual students construct racing cars from
                                              Styrofom food trays and power them with the
                                              thrust of an inflated balloon. In three racing
                                              trials, the racers shoot along a straight course
                                              and the distance the racers travel is measured.
                                              Between trials, students redesign their racers
                                              to improve their performance and solve any
National Science Content Standards:           “mechanical” problems that crop up. At the
  Unifying Concepts and Processes             conclusion of the activity, students submit a
      • Change, constancy and measurement.    detailed report on their racer design and how it
  Science as Inquiry                          performed in the trials.
      • Abilities to do scientific inquiry.
  Physical Science                             Materials:
      • Positions and motion of objects.       Styrofoam food trays (ask for donations
      • Motion and forces.                        from local supermarkets)
  Science and Technology                       Small plastic stirer straws (round cross
       • Abilities of technologic design.         section) - 2 per racer
                                               Flexi-straws - 3 per racer
National Mathematics Content Standards:        4 or 5 inch round balloon
       • Number and Operations                 Masking tape
       • Geometry                              Sharp pencil
       • Measurement                           Scissors (optional)
       • Data Analysis and Probability         Ruler
                                               Meter stick or metric measuring tape for
National Mathematics Process Standards:           laying out race course
       • Problem Solving                       Sandpaper (optional)
       • Reasoning and Proof
       • Communication
       • Connections
                                              Management:
                                              Each student will need a Styrofoam food tray.
       • Representations
                                              Request donations from your local supermarket.
                                              Ask for thicker trays (about 3/16th inch thick).
                                              Yellow trays used for poultry work well. Waffle-
                                              bottom trays are acceptable. Although the
                                              trays can be cut using scissors, save the
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scissors for trimming. It is much easier to                           Second Law
score the Styrofoam with a sharp pencil and               Force equals mass times acceleration
then break the pieces away. Score lines can                            (or f = ma).
be continuous or the tip of the pencil can be
punched into the Styrofoam to make a dotted                             Third Law
line. Demonstrate the scoring process to your             For every action there is an equal and
students. After the pieces are broken out, the                      opposite reaction.
edges are smoothed. Wheels can be smoothed
by rolling them on a hard surface while applying             Rest and Motion, as they are used in
pressure. Sandpaper also can be used for             the first law, are relative terms. They mean rest
smoothing.                                           or motion in relation to surroundings. You are
         Lay out a race course in a large            at rest when sitting in a chair. It doesn’t matter
open space or hallway. The space can be              if the chair is in the cabin of a jet plane on a
carpeted but textured carpets interfere with         cross-country flight. You still are considered to
the movements of the racers. Stretch out a           be at rest because the airplane cabin is moving
10 meter-long line of masking tape and mark          along with you. If you get up from your seat on
10-centimeter intervals. If you have a 10 meter      the airplane and walk down the aisle, you are in
tape measure, just tape it to the floor.             relative motion because you are changing your
         Double check the taping of the balloon      position inside the cabin. Inertia is the related
to the straw. The balloon should be completely       principle first described by Galileo that states
sealed or it will be difficult to inflate and some   that all matter, because of its mass, resists
of its thrust will be lost through the leaks. Pre    changes in motion. An object at rest will stay
inflating the balloon will loosen it and make it     at rest and an object in motion will continue in
easier to inflate through the straw.                 motion until acted upon by an outside force.
         Guide students through the redesign                 Force is a push or a pull exerted on
process to improve their racers. If their racers     an object. For example, you have to pull a
are not running well, ask them what they think       refrigerator to clean behind it and push it to
the problem might be. Then, ask them what            return it to its place. In the case of rockets,
they can do to address the problem. Typical          force usually is exerted by burning rocket
problems include having wheels fastened              propellants that expand explosively as they
too tightly against sides of the cars (friction),    rush out the rocket engine. Have students slide
crooked mounting of wheels or axles (racer           textbooks across their desktops. It takes a push
curves off course), axles not mounted in center      or a pull force to move (motion) the books.
of wheel or wheels not round (like “clown car”       When the force stops, friction (another force)
wheels).                                             stops the books from moving.
                                                             Balanced and Unbalanced Force
Background:                                          refers to the sum total or net force exerted on
The rocket racer is an excellent demonstration       an object. The forces on a coffee cup sitting
of Newton’s Laws of motion. Before we                on a desk, for example, are in balance. Gravity
describe how to to conduct the activity, let us      exerts a downward force on the cup while the
review the laws themselves.                          desk exerts an upward force, preventing the
                                                     cup from falling. The two forces are in balance.
                    First Law                        Reach over and pick up the cup. In doing so,
  Objects at rest remain at rest and objects in      you unbalance the forces on the cup (you exert
     motion remain in motion in a straight           an upward force greater than the downward
         line unless acted upon by an                force of gravity.) If you hold the cup steady, the
               unbalanced force.                     force of gravity and your muscle force are in
                                                     balance again.
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        How can you tell if forces are balanced
or unbalanced? Let’s use a soccer ball as an
example. If the soccer ball is at rest on the
playing field, the forces are balanced. Kick the
ball and the forces are unbalanced—the ball
is moving in an arcing flight in which its speed
and direction are changing constantly. However,
if you were in space far from any gravitational
field and kicked the ball, it would travel forever
in a straight line at a constant speed. In that
case, the forces on the ball are balanced again.
Unbalanced forces result in a change in an
object’s motion. Motion does not change when
forces are balanced.
        Mass is a measure of the amount of           Demonstrate the action-reaction principle
matter contained in an object. The mass of           (Newton’s Third Law) by inserting a pin through
an object does not change if the object is           a straw and into a pencil eraser. Inflate the
not altered in any way. Weight, however, can         balloon and it will pnwheel around the pencil
change depending upon the location of the            as air rushes out. Compare this to the straight
object. A 120 pound object on Earth weighs           thrust produced by the balloon in the rocket
only 20 pounds on the Moon. Weight is                cars, when students build their cars.
dependent on the strength of the gravitational
field acting on it. The mass of that object                 The same idea applies to the way the
(about 55 kilograms) is the same on Earth or on      rocket racer is propelled. The car will sit at
the Moon.                                            rest on the floor until an unbalanced force is
                                                     exerted on it (First Law). Air is compressed
        Acceleration relates to motion. It           inside the balloon by the balloon’s elasticity.
means a change in motion. Usually, change
                                                     When the balloon is released, it returns to its
refers to increasing speed, like what occurs
                                                     original uninflated size by propelling the air out
when you step on the accelerator pedal of a car.
                                                     its nozzle. The amount of force produced is
Acceleration also means changing direction.
                                                     determined by how much air (mass) is expelled
This is what happens on a carousel. Even
                                                     by the ballloon and how fast the air rushes out
though the carousel is turning at a constant
                                                     (Second Law) The action force of the expelling
rate, the continual change in direction of
                                                     air produces a reaction force that pushes the
the horses and riders (circular motion) is an
                                                     racer in the opposite direction. The racer’s
acceleration.
                                                     wheels reduce friction with the floor and the
        Action is the result of a force. A cannon    racer takes off down the race course. (Third
fires, and the cannon ball flies through the air.    Law)
The movement of the cannon ball is an action.               Although the rocket racer seems simple,
Release air from an inflated balloon. The air        there are many challenging complexities in
shoots out the nozzle. That is also an action.       its operation. In principle (Newton’s Second
        Reaction is related to action. When the      Law of Motion), the less mass the car has, the
cannon fires, and the cannon ball flies through      greater its acceleration will be. Generally, large
the air, the cannon itself recoils backward.         rocket racers do not perform as well as less
That is a reaction. When the air rushes out of       massive racers. However, very small racers
the balloon, the balloon shoots the other way,       are limited by other factors. Vehicles with short
another reaction.                                    wheel bases tend to circle or partially lift off the
                                                     floor. Balance becomes a problem. The mass

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of the balloon may cause the car to tilt nose           graphs and what data they should collect.
down to the floor, causing a poor start.                Using a smart board or overhead projector,
                                                        show how to fill in the graphs.
       The engineering design of the racer is        5. Distribute materials and instruct students
very important. Many designs are possible               to begin designing their cars. Once their
including wide, narrow, and I-beam shaped               designs are completed, have them begin
bodies and three, four, or even six wheels.             construction. While students are building
Students will have to review the trade-offs of          their cars, lay out the racer course (or prepare
their designs. For example, an extra-long body          prior to day two).
may provide a straighter path, but it might travel
a shorter distance as a result.                      Day Two
                                                     6. When students’ racers are ready, have one or
Procedure:                                              two students at a time inflate their balloons
Day One                                                 and pinch off the end of the straw to keep
1. Begin this activity by showing your students         the air in. Have them place their racers
   the balloon-powered pinwheel described               just behind the starting line and release the
   on page 3. Begin with the ballon uninflated.         straws. Regardless of how much curving a
   Ask...Is anything happening? (Newton’s First         racer does, the measured distance is how far
   Law and the principle of inertia) Inflate the        along the straight line of the race course the
   balloon and release the straw. Ask, what             race reached. It’s OK if they aim their cars
   happened? (Newton’s Third Law of Motion.)            the wrong direction. They will get it right the
   Share Newton’s Third Law of Motion with              next time!
   your students.                                    7. Ask students to identify which movements
2. Provide students with the How To Build               represent the action component (air rushing
   A Rocket Racer Sheet. Go over the                    out of the balloon) and reaction component
                                                        (car moving) of their racers. Challenge
  Tip: Students can make their wheels                   students to think about what might happen to
  rounder by pressing the edge of each                  a moving racer if there were no forces, such
  wheel on a hard surface and rolling it.               as friction, acting against its movement (the
                                                        racer would continue traveling).
                                                     8. Post distance records after each trial to
   construction steps and demonstrate how to            motivate students to improve their racers.
   snap out parts, mount the wheels, and how            Allow groups time to brainstorm and modify
   to attach the straw to the balloon. Refer to         their racers after each trial.
   the management section for more details.          9. After each racer has been modified (if
3. Stress that the racer shown in the                   necessary) and run three times, have
   instructions is a basic racer. Many designs          students complete their data sheets and
   are possible. Have them think up their own           sketch their final designs on the design
   designs and draw them on the design sheet.           sheets.
   Students’ racers do not have to have four         10. Wrap up the activity by having students
   wheels! You may want to review Newton’s              report on their designs and what worked
   Second Law with students to help them think          and didn’t work. How did you improve your
   about which variables might influence the            racer? What other things might you do to
   performance of their racers.                         make it travel farther? Explain how your
                                                        racers used Newton’s Laws of Motion.
4. Review the Rocket Racer Data Sheet and
   make sure students know how to fill out the


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11. To conclude, review the relationships               cars that are balanced with the extra load?
  between force, mass and acceleration                • Have students control the thrust of their
  for students, in light of how their designs           balloons by inflating them to the same
  affected the performance of their racers. Ask,        diameter each time. How can students
  do you think rocket designers have to think           ensure that the balloon is always the same?
  about similar design features?                      • Using the same materials, what other devices
                                                        can be created that demonstrate the action-
Further Discussion:                                     reaction principle of Newton’s Third Law of
• Would it be a good idea for automobiles to be         Motion?
  powered by rocket engines?
  If one rocket powered automobile were the
  only vehicle on the road, it would work fine.
  However, imagine rush hour traffic loaded
  with rocket cars. Each would blow exhaust
  gas at the vehicles to the rear.
• How are the wheels on a rocket racer similar
  to and different from wheels on a regular
  automobile?
  Rocket racer wheels simply reduce friction
  of the racer with the ground. They turn
  when the air coming from the balloon exerts
  a thrust. Wheels for an automobile also
  permit the car to roll across the ground, but
  the thrust of an automobile depends upon
  friction. The engine turns the wheels and
  friction with the rubber and the pavement
  transmits the action force so that the car roll
  forward.

Assessment:
• Review student Rocket Racer Data Sheets
  and Design Sheets.
• Have students write an explanation of all three
  of Newton’s Laws of Motion using their rocket
  racers as examples.



Extensions:
• Hold Rocket Racer drag races. Lay out a 3-
  meter-long course. The fastest car is the one
  that crosses the finish line the first. Calculate
  racer average speed by timing start to finish
  with a stopwatch (e.g. Four seconds to go
  three meters = 0.75 m/second or 2.7 km/h).
• Have students try multiple balloons for
  additional thrust. How will students design


                                                                                                5
How To Build A Rocket Racer
1. Lay out your pattern on the Styrofoam tray.
  You will need a racer body and wheels. Use
  a pencil point to score the Styrofoam. Snap
  out your pieces and smooth them. Make
  sure your wheels are round! Use sandpaper
  to round the wheels OR press them on a hard
  surface and roll them.
                                                   4. Mount the wheels to the bottom of the racer
                                                     body with masking tape. Only tape the larger
                                                     straw. The axle straws must be free to rotate.
2. Punch a small hole in
  the center of each wheel
  with the pencil. Push
  the axle (stirrer) straw
  through the hole of one
  wheel so that it extends
  1 cm on the other side.
  Pinch a piece of masking
  tape around the end of
  the straw and smooth
  it on to the wheel. Do
  the same for the second
  axle. Do not add wheels                          5. Blow up the balloon and then let the air
  to the other ends yet!                             out. Next, slip the straw into the balloon as
                                                     shown. Use masking tape to seal the balloon
                                                     nozzle to the straw. Squeeze the tape tightly
                                                     to seal all holes. Test the seal by blowing up
                                                     the balloon again through the straw.
3. Cut two large straws to the size you want
  and slide them over the two axles you just
  made. Mount the remaining wheels on the
  other ends of the axles.




6. Mount the balloon and straw to the racer with masking tape as shown. Be sure the end of the
  straw (rocket nozzle) extends off the end of the racer body.
                                                                                                 6
Wheel Patterns
Cut out the desired wheel size. Trace the wheel outline on the
styrofoam. Punch the pencil point through the cross to mark
the center.




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    Name: __________________                  TOP VIEW



          Rocket Racer
          Design Sheet

    Draw a diagram showing your best design
    for a rocket racer.

    Show your racer as seen from the
    front, top, and side.

    Each square on the graphs = 1cm.




    FRONT VIEW                                SIDE VIEW




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    Rocket Racer Data Sheet                                                               Name:     __________________
                                                 Shade in the graph showing how far your rocket racer traveled in centimeters.
    Rocket Racer
    Trial #1
                     0        100        200        300         400          500          600          700          800          900   1,000 cm
     Describe how your rocket racer ran (straight, curved, circles, stuck, etc.).

     Did your racer perform as well as you hoped? Explain why or why not.


    Rocket Racer
    Trial #2
                     0        100        200        300         400          500          600          700          800          900   1,000 cm
     How did you improve your rocket racer?

     Predict how far your racer will run. ____________ cm
     Describe how your rocket racer ran.

     Did your improvements work? Explain why or why not.



    Rocket Racer
    Trial #3
                     0        100        200        300         400          500          600          700          800          900   1,000 cm
     How did you improve your rocket racer?

     Predict how far your racer will run. ____________ cm

     Describe how your rocket racer ran.




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     Did your improvements work? Explain why or why not.

								
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