Foam Rocket. Rocket Activity. Objective Students will learn about rocket stability and trajectory with rubber band-powered foam rockets.

Transcription

1 Rcket Activity Fam Rcket Objective Students will learn abut rcket stability and trajectry with rubber band-pwered fam rckets. Descriptin Students will cnstruct rckets made frm pipe insulating fam and use them t investigate the trajectry relatinship between launch angle and range in a cntrlled investigatin. Natinal Science Cntent Standards Unifying Cncepts and Prcesses Evidence, mdels, and explanatin Change, cnstancy, and measurement Science as Inquiry Abilities necessary t d scientific inquiry Physical Science Psitin and mtin f bjects Mtins and frces Science and Technlgy Abilities f technlgical design Natinal Mathematics Cntent Standards Number and Operatins Algebra Gemetry Measurement Data Analysis and Prbability Natinal Mathematics Prcess Standards Reasning and Prf Cmmunicatin Cnnectins Materials 30 cm-lng piece f plyethylene fam pipe insulatin (fr 1/2 size pipe ) Rubber band (size 64) Styrfam fd tray 3 8 plastic cable wraps 75 cm f rdinary string Scissrs Meter stick Press tack Washer r nut Quadrant plans printed n card stck Rcket cnstructin instructins Experiment data sheet Masking tape Launch recrd sheet Fr class - tape measure Management Select a large rm with a high ceiling fr the launch range, such as a cafeteria r gymnasium. Place markers n the flr at 1 meter intervals starting at 5 meters and ging t 20 meters. If it is a calm day, the investigatin can be cnducted utside. Althugh the rckets can be launched utside n windy days, the wind becmes an uncntrllable variable that will invalidate the results. Prepare sme sample rcket fins t shw hw they are cnstructed. Refer t the cnstructin 72

2 page fr details. Befre cnducting the investigatin, review the cncept f cntrl. In this investigatin, cntrl will be hw much the rubber band is stretched when launching the rckets. The experimental variable will be the angle f launch. Students will cmpare the launch angle with the distance the rcket travels. Organize students int teams f three. One student is the launcher. The secnd student cnfirms the launch angle and gives the launch cmmand. The third student measures the launch distance, recrds it, and returns the rcket t the launch site fr the next flight. The experiment is repeated twice mre with students switching rles. The distances flwn will be averaged, and students will predict what the best launch angle shuld be t btain the greatest distance frm the launch site. Backgrund The fam rcket flies ballistically. It receives its entire thrust frm the frce prduced by the elastic rubber band. The rubber band is stretched. When the rcket is released, the rubber band quickly returns t its riginal length, launching the fam rcket in the prcess. Technically, the fam rcket is a rcket in appearance nly. The thrust f real rckets typically cntinues fr several secnds r minutes, causing cntinuus acceleratin, until prpellants are exhausted. The fam rcket gets a quick pull and thrusting is ver. Once in flight, it casts. Furthermre, the mass f the fam rcket desn t change in flight. Real rckets cnsume prpellants and their ttal mass diminishes. Nevertheless, the flight Tip Be sure the range-measuring student measures where the rcket tuches dwn and nt where the rcket ends up after sliding r buncing alng the flr. In flight, fam rckets are stabilized by their fins. The fins, like feathers n an arrw, keep the rcket pinted in the desired directin. If launched straight up, the fam rcket will pint upward until it reaches the tp f its flight. Bth gravity and air drag put act as brakes. At the very tp f the flight, the rcket mmentarily becmes unstable. It flps ver as air catches the fins and becmes stable again when it falls back nse frward. When the fam rcket is launched at an angle f less than 90 degrees, it generally remains stable thrugh the entire flight. Its path is an arc whse shape is determined by the launch angle. Fr high launch angles, the arc is steep, and fr lw angles, it is brad. When launching a ballistic rcket straight up (neglecting air currents) the rcket will fall straight back t its launch site when its upward mtin stps. If the rcket is launched at an angle f less than 90 degrees, it will land at sme distance frm the launch site. Hw far away frm the launch site is dependent n fur things. These are: gravity launch angle initial velcity atmspheric drag f a fam rcket is similar t that f real rckets. Gravity causes the fam rcket t decelerate Its mtin and curse is affected by gravity and as it climbs upward and then causes it t by drag r frictin with the atmsphere. The accelerate as it falls back t the grund. The ability t fly fam rckets repeatedly (withut launch angle wrks with gravity t shape the refueling) makes them ideal fr classrm flight path. Initial velcity and drag affects the investigatins n rcket mtin. flight time. The launch f a fam rcket is a gd In the investigatin, students will demnstratin f Newtn s third law f mtin. cmpare the launch angle t the range r The cntractin f the rubber band prduces distance the fam rcket lands frm the an actin frce that prpels the rcket frward launch site. Launch angle is the independent while exerting an ppsite and equal frce n variable. Gravity can be ignred because the the launcher. In this activity, the launcher is a acceleratin f gravity will remain the same fr meter stick held by the student. all flight tests. 73

3 Atmspheric drag can be ignred because the same rcket will be flwn repeatedly. Althugh students will nt knw the initial velcity, they will cntrl fr it by stretching the rubber band the same amunt fr each flight. The dependent variable in the experiment is the distance the rcket travels. Assuming student teams are careful in their cntrl f launch angles and in the stretching f the launch band, they will bserve that their farthest flights will cme frm launches with 75 an angle f 45 degrees. They will als bserve that launches f 30 degrees, fr example, will prduce the same range as launches f 60 degrees. Twenty degrees will prduce the same result as 70 degrees, etc. (Nte: Range distances will nt be exact because f slight differences in launching even when teams are very careful t be cnsistent. Hwever, repeated launches can be averaged s that the ranges mre clsely agree with the illustratin. Prcedures Cnstructing a Fam Rcket 1. Using scissrs, cut ne 30-cm length f pipe fam fr each team. 2. Cut fur equally spaced slits at ne end f the tube. The slits shuld be abut 8 t 10 cm lng. The fins will be munted thrugh these slits. 3. Tie a string lp that is abut 30 cm lng. 4. Slip ne end f a cable wrap thrugh the string lp and thrugh the rubber launch band Launch angle vs. range fr rckets with the same initial launch velcity Jin the cable wrap t frm a lp and tighten it dwn t a circle apprximately 1 t 2 cm in diameter. The end f the wrap can be trimmed ff with scissrs r left. 5. Thread the cable wrap with string and rubber launch band thrugh the hle in the fam tube. The string shuld stick ut the rear end f the rcket and the rubber band ut the nse. Psitin the plastic lp abut 3 cm back frm the nse. 6. Tighten the secnd cable wrap securely arund the nse f the rcket. It shuld be psitined s that the cable wrap lp inside the rcket is unable t be pulled ut the nse when the rubber band is stretched. Cautin students nt t pull n the string. The string shuld nly be pulled during launches when the rubber band is held frm the ther end. Trim ff the excess cable wrap end. 7. Cut fin pairs frm the fam fd tray r stiff cardbard. Refer t the fin diagram. Launch string lp Plastic cable wrap Plastic cable wrap Internal plastic cable wrap Launch rubber band 74

4 Cut slts the same width as the thickness f the fin stck. Nest fins tgether. Bth fin pairs shuld be ntched s that they can be slid tgether as shwn in the diagram. Different fin shapes can be used, but they shuld still nest tgether. 8. Slide the nested fins int the slits cut in the rear end f the rcket. Make sure the string lp hangs ut the engine end. 9. Tighten the third cable wrap arund the rear f the rcket. This will hld the fins in place. Trim ff the excess cable wrap end. Prcedure Making the Launcher 1. Print the quadrant pattern (page 78) n card stck paper. 2. Cut ut the pattern and fld it n the dashed line. 3. Tape the quadrant t the meter stick s that the black dt lies directly ver the 60 cm mark n the stick. 4. Press a push tack int the black dt. Different fin shapes can be used Launcher ready fr a 45-degree angle launch

5 5. Tie a string t the push tack and hang a small weight, such as a nut r a washer, n the string. The weight shuld swing freely. 6. Refer t the diagram t see hw the launcher is used. Discussin Why didn t the experiment prtcl call fr launching at 0 and 90 degrees? Assuming a perfect launch, a rcket launched straight upwards shuld return t the launch pad. Any variatin in the impact site will be due t air currents and nt t the launch angle. A rcket launched hrizntally will travel nly as lng as the time it takes t drp t the flr. Shuldn t the rcket be launched frm the flr fr the experiment? Yes. Hwever, it is awkward t d s. Furthermre, student teams will be measuring the ttal distance the rcket travels, and cnsistently launching frm abve the flr will nt significantly affect the utcme. Students will have t determine initial velcity. If available, an electrnic phtgate (science lab prbeware) with timer can be used fr determining the initial velcity. Otherwise, challenge students t devise a methd fr estimating initial velcity. One apprach might be t launch the rcket hrizntally frm a tabletp and measure the hrizntal distance the rcket travels as it falls t the flr. Using a stpwatch, measure the time the rcket takes t reach the flr. If the rcket takes 0.25 secnds t reach the flr and traveled 3 meters hrizntally while ding s, multiply 3 meters by 4. The initial velcity will be 12 meters per secnd. Students shuld repeat the measurement several times and average the data t imprve their accuracy. (This methd assumes n slwing f the rcket in flight due t air drag.) Different kinds f fins can be cnstructed fr the fam rcket. Try creating a space shuttle rbiter r a future rcket plane fr explring the atmsphere f ther planets. Assessment Have student teams submit their cmpleted data sheets with cnclusins. Have students write abut ptential practical uses fr the fam rcket (e.g., delivering messages). Extensins Fr advanced students, the fllwing equatin can be used fr estimating ranges. (g is the acceleratin f gravity n Earth) Range = V g sin 2A V = Initial Velcity g = 9.8 meters/secnd 2 A = Launch Angle 76

6 Cut fur slits 8 cm lng. 1 Build a Fam Rcket 30 cm 2 Jin 30 cm string lp and rubber band with cable wrap. String Rubber band Cable wrap lp Cut ut fins with ntches. 5 Slide fins tgether. Slip string, cable wrap lp, and rubber band inside. 3 6 Clse ff end with cable wrap (tight!). 4 Slide fins int slits. 7 Clse ff end with cable wrap (tight!) Ready fr flight! 8 77

7 Launcher Quadrant Pattern (Actual Size) 60 cm (r 24 inches) 0 10 Fld n dashed line. Lay fld n upper edge f meter stick and wrap paper arund t the ther side. The black dt f the prtractr shuld be placed n the 60 cm mark f the stick. Tape ends t hld the prtractr in place

8 Rcket Range Experiment Team Member Names: 1. Assign duties fr yur team. Yu will need the fllwing psitins: Launch Directr, Launcher, and Range Officer. (Team members will switch jbs later.) 2. First Launch: Launcher - Attach the rcket t the launcher and pull back n string until its tail reaches the 60-cm mark. Tilt the launcher until it is pinting upwards at a angle f between 10 and 80 degrees. Release the rcket when the launch cmmand is given. Launch Directr - Recrd the angle n the data table. Give the launch cmmand. Recrd the distance the rcket travels. Range Officer - Measure the distance frm the launcher t where the rcket hits the flr (nt where it slides r bunces t). Reprt the distance t the launch directr and return the rcket t the launcher fr the next launch. 3. Repeat the launch prcedures fur mre times but fr different angles f frm 10 and 80 degrees. 4. Run the entire experiment twice mre but switch jbs each time. Use different launch angles. 5. Cmpare yur data fr the three experiments. Data Table 1 Data Table 2 Data Table 3 Launch Angle Distance Launch Angle Distance Launch Angle Distance Frm yur data, what launch angle shuld yu use t achieve the greatest distance frm the launch site? Test yur cnclusin. Why didn t the instructins ask yu t test fr 0 and 90 degrees? 79