Bottle Rockets (150 points)

 

Problem/Purpose: To create a bottle rocket that will fly straight and will stay in the air for as long as possible.

Background Information:

A squid propels itself by filling its body with water and ejecting it backwards in order to move forwards. This is the principle used by rocket engineers. Space rockets use fuels that are burned in a chamber shaped rather like a bottle, with the neck pointing backwards. The burning fuel produces a large quantity of gas that is further expanded by the heat generated and this is ejected through the neck (or nozzle) of the “bottle” (normally called the combustion chamber) at a very high velocity, propelling the rocket in the opposite direction (one of Newton’s laws).

The bottle rocket, like the squid, uses water as the driving agent and compressed air instead of heat to provide the energy.

For the technically minded, if the pressure in the bottle at launch is about 18 x 104 N/m2 (or about 25 psi). The water is forced through a nozzle with a cross sectional area of about 1cm2 and this produces a theoretical thrust of about 18 Newtons (about 3.9lbs) at launch. As the water is ejected the bottle rocket gets lighter resulting in an increased acceleration or ‘g’ force. This increasing ‘g’ force is one of the more unpleasant aspects of space flight that astronauts have to endure; a rocket leaving the earth’s atmosphere would have to keep up this increasing acceleration for some time. The bottle rocket expels its charge of water in about 1 second so DON’T WORRY, IT’S NOT LIKELY TO GO INTO ORBIT!

State Newton’s three laws of motion (3 points)

            1.

            2.

            3.

State Pascal’s Principle (1 point)

            1.

Materials:

Rules:

Part I: Constructing Your Bottle Rocket

Below is a diagram of how your bottle rocket should be put together:

                                                                                               Stability weight goes here as well..

    

A)   Sleeve

a.     A slit will be made in the two liter bottle for the sleeve.

b.     Using the slit, cut the top off of this bottle. Do not cut both bottles!

c.     You may also leave the bottom on the sleeve, if you want, to keep the rounded end as your nose.

d.     Attach the sleeve to the uncut bottle using duct tape.

B)    Stability

a.     Ideally you want your rocket to fly straight or it will reduce the rocket’s performance. Your rocket’s center of gravity is near the top middle of your rocket and we want to move it more toward the top without adding too much weight.

b.     Tape small objects to the bottom of your intact bottle, or place a chunk of mud or clay to the bottom.

C)    Nose Cone

a.     To construct the nose cone for you rocket use a piece of card stock.

b.     Draw a circle with a radius of 6 inches, and cut it out.

c.     Cut one slit from the outer edge of the circle to the center.

d.     Fold the poster board until it creates a cone that fits on top of you rocket.

e.     You can make a different shaped nose if you would like: such as a curved nose, a pointed nose, or an elongated nose.

f.     Attach the nose cone to the sleeve, use duct tape.

D)    Fins

a.     Create 3, 4, 5 or 6 fins to put on the pressurized bottle.

b.     Fins can be created from old cds, plastic bottle pieces, poster board, manila folders, card stock, or cardboard.

c.     Fins need to be strong, and not flexible.

d.     Fasten the fins to your rocket using tape. The fins need to be spaced equally apart.

E)    Parachute (not necessary, but you can try one if you want)

a.     Take a large garbage bag and lay it out flat.

b.     Cut a large circle out of the bag.

c.     Put 16 pieces of masking tape around the edges of the bag, evenly spaced.

d.     Punch one hole through each piece of tape. Use a reinforcement tab around each hole.

e.     Attach sixteen 32-inch long strings to the bag, evenly spaced.

                                          i.    Put 4 strings on your parachute. Tie these four strings together at the base of the strings.

                                         ii.    Repeat 3 more times. (You should have 4 groups of 4 strings)

                                       iii.    Use duct tape to tape the ends of the strings to your pressurized bottle.

f.     Fold the parachute and strings so that it makes a “z” shape.

                                                   

 

 

 

 

 

 

 

 

 

 

F)    Water                         

a.     Look at the graph that has calculated the optimum amount of water for different size bottles.

b.     To put it into practice, weigh in the optimum amount of water and put a piece of tape along the side of the rocket where the water line comes to.

c.     Screw a top on, invert it and make another mark (in such a way that you will not be confused - possibly using an arrow pointing upwards). This will make life easier when in the field and you haven't got access to the scales and you can just fill the water up to this new line.

d.     Or you can just put in however much water you want. Too little, not enough thrust...too much, too heavy. Anywhere from 450 ml to 750 ml seems to work well.

Part II: Launching the Bottle Rocket

Safety: 

Participation:

 

Procedure:

1)     Get your rocket ready to launch.

2)    Fill your rocket with water. Record how much water you put in your bottle. Put the cap on the end of the bottle

3)    Place your rocket on the launch pad. Insert the nails firmly. Pump up your rocket to 70-90 PSI.

4)    Wear safety goggles. Be very careful when pulling the pin from the launcher. Pull to the side of your body.

5)    Sixteen students will each have a stopwatch.

a.     8 students: Start the stopwatch when the rocket is launched, stop timing when the rocket reaches its maximum height (or when the parachute deploys). Record the time in the appropriate column in your data table.

b.     Other 8 students: Start the stopwatch when the rocket is launched, stop timing when the rocket hits the ground. Record this time in the appropriate column in your data table.

6)    Sixteen students will be altitude trackers.  Members will work in pairs at a distance of 50 meters (166.66 ft) from the launch site.

a.     Each member will sight the rocket in their altitude tracker.  When the rocket gets to it’s highest point, pull the trigger or Point the protractor at the rocket, hold the string, record the angle. No # should be greater than 90˚.

b.     Record the degrees of altitude in the appropriate column in your data table. If you have the blue clinometers, record the altitude in meters. The number on the altitude finder will need to be divided by 3 to find the actual distance or altitude of the rocket. If you have a protractor, you will need to subtract your number from 90˚ to get the actual degrees. A high flying rocket will be closer to 90˚, a low flying rocket will be closer to 0˚.

7)    Repeat steps 1-6.

 

Measuring The Angle Of Elevation
Measuring the height achieved in a flight is not so easy. The instrument we use is called a CLINOMETER and consists of a pair of sights on a rod and a protractor with a pendulum attached to record the angle of elevation of the rocket.

To use the clinometer the operator stands a known distance from the launch site and follows the flight of the rocket with the sights. At the very top of the flight (the APOGEE) the plumb bob is trapped against the protractor with a finger and the angle is read off and recorded. The height of the rocket at apogee is then calculated by the following formula:


HEIGHT = DISTANCE FROM LAUNCH x
TANGENT of ANGLE of ELEVATION

 

 

Calculating The Height
In practice it is best to use four clinometers spaced evenly around the edge of a 25m radius circle centered on the middle of the rocket range. The four readings are taken simultaneously and averaged to give a more accurate result. We will only be using 2 clinometers, and averaging the results.  

Use the degree scale to calculate altitude. Altitude = Angle tangent x Baseline distance. Ex. If the angle is 40°, the tangent is 0.838, you multiply it by 50 m, the altitude is 41.9 meters. Table of tangents 


using a clinometer to find the angle of elevation of a rocket at apogee

 

 

Attach the parachute to the bottle with pieces of strong tape.

 

 

 

Team Members Names

Launch 1   Time (s)

Launch 1   Angle (˚degrees)

Launch 2   Time (s)

Launch 2  Angle (˚degrees)

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15

 

 

 

 

 

16

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Data: (70 points)

Launch Information for     ____________________   &   _________________________ Per.______

 

Mass of Rocket

(g)

Mass of Rocket

Convert g to kg

Amount of water for 1st launch (ml)

Amount of water for 2nd  launch (ml)

# of fins and shape of fins (draw it)

Weight in nose cone (state yes & object or no)

 

 

 

 

 

 

 

 

Anything special you did for your rocket:________________________________________________________

______________________________________________________________________________________

 

Team Members Names

Launch 1   Total Time (s)

Launch 1   Angle (˚degrees)

Launch 2   Total Time (s)

Launch 2  Angle (˚degrees)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Average

 

 

 

 

Average of  the Averages

 

Find the average of the 2 Averaged Launch Times:

 

Time to Peak-(Divide the average time by 2):

Find the average of the angles for 2 launches:

Angle A-Subtract this number by 90.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Launch #

 

Pressure in PSI

Pressure in Pascals

(Multiple PSI : 1 pound per square inch= 6,895 Pa)

1

 

 

2

 

 

Average

 

 

 

Calculations: Complete the following calculations. Be sure to show all of your work, use the correct units and significant digits.

 

1)     Distance using time: (4 points) How far the bottle rocket traveled (from the launch pad to its maximum height.)         S= ˝ a x t2     For time to peak take total time and divide by 2.

Distance = ˝ 9.81 m/s2 × (total time – time to peak) 2

d = _______________

 

2)    Distance using tan θ (4 points) How far the rocket traveled (from the launch pad to its maximum height.) Average of the angles for 2 launches _______ - 90˚ = Angle A_________˚

Find the Angle A number on the tan θ table. Tangent of A = ______

Distance = Tangent of A × 50m

d =_______________

 

3)    Initial Velocity: (4 points) Vi = 9.8 m/s2 × time to peak=     __________________________

 

 

4)    Average velocity (4 points)          Formula: v =  distance  ÷ time to peak

 

  v =_________________

 

5)    Momentum (4 points)       Formula: M = mass of rocket(kg) x velocity

 

                     M =_________________

 

6)    Thrust ( 4 points)  Formula: Thrust = (π/2) = (Pressure in Pascals) x (nozzle diameter) 2

Thrust = (1.57) x (pa) x (0.022m) 2

Thrust = ________________

 

Analysis Questions: (10 points total)

1)     Why didn’t you fill the pressurized body all the way up with H2O? Explain using Newton’s 1st Law of motion.

2)    Did the rocket and the water move in the same direction? Explain what happened using Newton’s 3rd Law of Motion. (What was the action and reaction?)

3)    How does the momentum of the rocket change as it lifts off? How does it change as it falls back to the ground?

4)    What forces act against the rocket’s momentum?

5)    What causes the rocket to fly skyward?

6)    Would a rocket launched in the mountains have a greater momentum or a rocket launched at sea level? Why?

7)    How does the difference in external pressure to internal pressure of the rocket affect its distance?

8)    How does Pascal’s Principle apply to your rocket?

9)    Where should the center of gravity be on your rocket in relation to the center of pressure?

10)  What factors help make your rocket stable?

 

RERUNS Conclusion (30 points):

 

 

 

 

 

 

 

 

Highest Flying Rocket Contest Hall of Fame

Name Year Total Time in Air (seconds)
    12 sec