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 1 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. 2 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 3 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 4 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. 7 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 8 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. 9 Did your improvements work? Explain why or why not.
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