Rocket Science: How High Can You Send a Payload?
AbstractRockets are definitively an engineering challenge. These amazing gravity-defying machines have lifted test material, people, and even animals into space. Feel like building one yourself? In this science project, you will transform a water bottle into an aerodynamic bottle rocket with two compartments, one for the fuel and one for a payload. You will then test how well it performs when lifting mass vertically up into the air. Ready, set, soar!
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Create an aerodynamic bottle rocket and use it to study the changes in maximum height reached when your rocket lifts a payload.
Rockets are very interesting pieces of machinery. They require quite a lot of power to beat gravity and lift themselves, and the things they carry, into space. In fact, you can create a model of one yourself, like the ones shown in Figure 1 from an empty plastic bottle that uses the same basic principles as real rockets to hoist itself into the air. Read on to discover these basic principles and to make your own bottle rocket.
Figure 1. Water bottle rockets like these use the same physics principles as real rockets to lift itself into the air.
Rockets use reaction engines to create a forward thrust. Newton's third law of motion explains why these engines work. This law states that for every action, there is an equal and opposite reaction. In the case of a rocket, the action is the engine ejecting mass at high speed backward. As a reaction, the rocket (engine) is pushed forward. This mechanism does not rely on the atmosphere and works very well in space.
Diagram showing action and reaction forces on a rocket. The action on the rocket is the force of fuel and exhaust being ejected from the bottom of the ship, while the reaction is the upward force applied to the body of the rocket.
Figure 2. Rockets use Newton's third law of motion to create a forward thrust; they eject mass backward at high speed (the action) to achieve a forward push (the reaction).
In aerospace (which is the branch of technology and industry concerning aviation and space flight), rocket engines eject exhaust gases produced through the combustion of fuel and accelerated to very high speed. Your bottle rocket will not use combustion; instead, it will eject water and air to create a forward thrust. Before liftoff, the bottle rocket will be partially filled with water and partially filled with air. A special bottle rocket launcher will allow you to add air to your bottle rocket. Air pressure—or how hard the air presses outward from the inside of the bottle—builds up in the bottle. Figure 3 illustrates how air pressure inside the bottle pushes on the walls of the bottle, as well as the liquid inside the bottle.
Figure 3. As you add air to a water bottle, pressure builds up inside. As a result, the plastic walls and the liquid inside the bottle feel a bigger push.
Note that you will measure the pressure in your rocket propulsion chamber in pounds per square inch (psi) because those are the units of measurement on a bicycle pump. However, psi is not a metric unit and in science the metric system is used. To use the metric system, record the pressure in pascals (Pa) also known as newtons per square meter (N/m2). The 30 psi used in this science project corresponds to 206,850 Pa or 207 kPa (because there are 1,000 Pa in 1 kPa). You can use an online calculator to make the conversion from pounds per square inch to pascals.
As you launch the rocket, the pressure created by adding air to the bottle pushes water and air out at high speed, propelling your rocket upward, as illustrated in Figure 4.
Figure 4. Water ejected from a bottle rocket (action) propels the rocket forward (reaction), according to Newton's third law of motion.
In aerospace, exhaust is formed entirely from propellants carried within the rocket before use. Fuel is stored and used in the propulsion chamber of the rocket. The bottle forming the body of your bottle rocket will serve as the propulsion chamber. In addition to fuel, rockets carry other items to space. This is referred to as payload. It is stored in the payload bay of the rocket. A nose is added to make the rocket more aerodynamic, which means decreasing the amount of air resistance experienced by the rocket during flight. In this science project, you will add a nose that can serve as a payload bay. Fins can be used to stabilize the rocket during flight. Figure 5 shows the different sections.
Diagram of a bottle rocket showing the nose and payload bay, propulsion chamber and fins. The bottom of the bottle (at top) is covered by the nose/payload bay, and body of the bottle is the propulsion chamber. Fins are attached to the neck of the bottle to help stabilize it during flight.
Figure 5. Nomenclature of the different sections of a bottle rocket.
In this science project, you will measure how adding payload (quantified by its mass) affects the maximum height your rocket reaches. To do so, you will need to add a payload bay to the most basic bottle rocket, an upside-down water bottle. In addition, you will improve the bottle rocket by making it more aerodynamic. More aerodynamic rockets have a straighter flight path, resulting in more reliable measurements of maximum height reached. The Procedure provides handy tips and hints on how to create your own rocket and provides the procedure to perform a scientific test on how payload affects maximum height reached. Ready to have a blast with your own rocket?
Terms and Concepts
- Reaction engine
- Newton's third law of motion
- Air pressure
- Pound per square inch (psi)
- Pascal (Pa)
- Propulsion chamber
- Payload bay
- What mechanism do rockets use to lift themselves off the ground and create a forward motion?
- If you launch two identical water bottle rockets, one with a filled payload bay and the other with an empty payload bay, in an identical way, which one do you think will go higher? Could you explain why?
- What do you think is the least aerodynamic part of the most basic water bottle rocket, meaning simply a bottle turned upside down?
- Benson, T. (n.d.). Water Rocket. National Aeronautics and Space Administration. Retrieved October 29, 2014.
- Lerardi, B. (18 June, 2007). VideoBrief: Newton's Laws of Motion illustrated with 3D animations. Science Vision. Retrieved November 17, 2014.
- Benson, T. (n.d.) Newtons Third Law. National Aeronautics and Space Administration. Retrieved November 4, 2014.
For more on how to measure the height a rocket reaches, see:
- University of Illinois, Department of Physics. (n.d.). Q&A: Height of a water rocket. The Ask Van. Retrieved October 29, 2014.
For help converting units of pressure, see:
- The Engineering Toolbox. (n.d.). Pressure Units Online Converter. Retrieved November 6, 2014.
Materials and Equipment
- Bottle Rocket Kit available from Amazon.com
- Soda bottle (2 L)
- Choose a bottle of a carbonated beverage or iced tea, as other bottles might not be strong enough.
- An altitude-tracker available from Amazon.com
- Water (4 gallons)
- (Optional) Empty 1 gallon bottles, helpful in case you need to transport water to the open space.
- Measuring cup (1 L)
- A cup or beaker with volume marks in milliliters (mL) like this measuring cup available from Amazon.com is preferred, but not essential.
- Funnel (to fill the 2 L bottle)
- Permanent marker
- Bicycle pump with pressure gauge, like this pump, available from Amazon.com.
- (Optional) Measuring tape
- Petroleum jelly
- Open outdoor space, like a park or athletic field, in which to launch your rocket
- Dimensions: At least 40 m (130 ft) long and 40 m wide
- Ground cover: Soft ground so the U peg to secure the launcher can be pushed into the ground.
- Various materials to create your bottle rocket:
- Plastic soda bottles (1–2 L) (2); choose a carbonated beverage or iced tea bottle, as other bottles might be made of flimsier plastic and not be strong enough to withstand the pressure created in the bottle rocket.
- Duct, craft paper and/or masking tape (at least 1.88 inches wide)
- Sandpaper, to roughen edges and ensure the tape sticks better
- Cardboard for potential fins
- Craft knife
- Stove with a hood and fan, or one that is in a well-ventilated area
- Pan with nonstick coating
- (Optional) Materials to decorate your bottle rocket:
- Permanent markers
- Spray paint (made especially for plastic)
- Newspaper to protect your work surface
- Decorative tape
- Sand (200 g to 1 kg)
- Scale, range 0–500 g; the Fast Weigh MS-500-BLK Digital Pocket Scale available from Amazon.com works well.
- Small bowl or container, to be used as a "measuring boat" in which to collect sand and measure its weight.
- Plastic juice bottle (500 mL); choose a bottle made of hard plastic.
- Adult supervision
- Lab notebook
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Caution: Here are some general safety guidelines you should read before you start this science project.
- This science project suggests melting the edges of a plastic bottle by heating them for a very short time. Melting plastic bottles is easy, but should be approached cautiously. Ask an adult to supervise you for this step, use the stove hood and fan, or a well-ventilated room, and never leave the bottle near the stove unattended.
- Select your observation spot such that you do not look toward the sun as you observe your launch. Looking into the sun can damage your eyes.
- Keep the pressure in the launch bottle below 50 psi at all times.
- Always use the U peg to secure the bottle rocket launcher to the ground before launching.
- Never lean over the bottle rocket while it is under pressure.
- Keep a safety zone of 4.5 m (about 15 ft) around the launcher clear of bystanders before each launch.
- Give the launch string a gentle, quick tug; a powerful yank might cause the launcher to come loose and launch in an unsafe direction.
- Important: In case launching fails, ask an adult to help you remove the bottle by following the launch failure procedure described in the bottle rocket launcher manual.
Creating the Basic Bottle Rocket
You will first select a bottle to serve as a propulsion chamber, the most basic part of your bottle rocket. The next section will help you transform this basic bottle rocket into a more aerodynamic rocket with payload bay.
- Empty a soda bottle (size 1–2 L) and rinse it with water. Remove and dispose of the outside wrapper and the cap.
- Make sure your bottle fits the launcher:
- Put the opening of your empty bottle on the launcher. Push the bottle down so it goes over the thin black ring, as illustrated in Figure 6.
- Pull the bottle back up as far as you can. The launch release latch should hold it in place, as shown in Figure 7. You might have to move the metal clip attaching the launch cord to the release handle out of the way.
Figure 6. The bottle rocket needs to be pushed over the black ring of the launcher, as shown in the figure on the right. In the image on the left, the bottle is not pushed down far enough.
Figure 7. The launch release handle needs to touch the bottle rocket to create a successful launch, as shown in the figure on the right.
- If your bottle fits the launcher, it can serve as the propulsion chamber of your bottle rocket. If it does not fit, repeat steps 1 and 2 with a different bottle.
- Make a mark with a permanent marker to indicate the initial water-air ratio for your rocket launches.
- In this science project, you will keep the initial ratio of water to air in your bottle rocket propulsion chamber constant. One-third of the volume will be filled with water and two-thirds will be filled with air. To facilitate launching, indicate this level on your bottle, as described in the next steps.
- Calculate one-third of the volume of your propulsion chamber.
- Hint: One-third of a volume of 2 L is about 0.7 L (700 mL); one-third of a volume of 1 L is about 0.35 L (350 mL).
- Measure the volume of water calculated in step 4.b. in your measuring cup.
- Note: If your measuring cup does not have metric volumes marked on it, measure 3 C for a 2 L bottle or 1.5 C for a 1 L bottle.
- Remove the bottle from the launcher once you have ensured it fits. Use a funnel to carefully pour the water into your bottle. Note: If you accidentally spill any, empty the bottle and measuring beaker and repeat steps 4.c. and 4.d.
- Place your bottle on a flat surface and wait for the water to stop moving, then trace the water line around the entire bottle with a permanent marker, as shown in Figure 8. Empty out the water once you have traced the line.
Figure 8. After filling the bottle to one-third of its volume, the water line is traced with a permanent marker.
Creating an Aerodynamic Bottle Rocket with Payload Bay
In this section, you use the Engineering Design Process to transform your basic water bottle rocket into an aerodynamic rocket with payload bay.
The requirements for your final product are as follows:
- The propulsion chamber of your rocket consists of the basic bottle rocket created in the previous section.
- The rocket should include a payload bay, which can be filled and emptied with sand. This is needed, as you will test your rocket with different payloads. In this science project, the nose will hold the payload.
- The payload bay should hold at least 200 g of sand.
- The rocket should launch in a nice straight line until it reaches its highest point and tumbles back down. This is referred to as a stable flight track.
You might want to read the hints below as you do your background research and brainstorm solutions, then choose the best one.
- Aerodynamic rockets generally have a more stable flight track.
- Adding fins stabilizes the rocket in flight, helping it to take a straight path up to its highest point.
- The top of a second bottle can serve as nose for your basic water bottle rocket. Adding a nose makes your rocket more aerodynamic. In this science project, this nose should also allow space for a payload.
- Bottle rockets can make a hard landing after a flight. Rockets need to be sturdy so they can absorb a shock. Alternatively, they can include a landing mechanism like a parachute, which opens as the rocket descends and ensures a soft landing.
- As you build your rocket, take into account that the propulsion chamber of your bottle rocket will expand slightly as you load the rocket with air before liftoff.
Figure 9 shows the main steps involved in the Science Buddies team's creation of a water bottle rocket.
Figure 9. As an example, this is a collage illustrating the steps in creating an aerodynamic water bottle rocket with payload bay. A first bottle serves as a propulsion chamber to which a nose (the top of a second bottle) is taped. The nose serves as payload bay and increases the aerodynamic qualities of the rocket.
Now you are ready to build. These tips might help you build a sturdy prototype:
- Heating a cut-open plastic water bottle will round the edges and make the bottle opening slightly smaller. This can be handy for creating a nice-fitting nose on a basic water bottle rocket. Melting plastic is easy, but needs to be approached cautiously. Let an adult supervise you for this step and use the stove hood and fan, or a well-ventilated room. To round the edges, place the cut side of a bottle on a heated, non-stick pan, as shown in Figure 10. Do not leave the bottle and stove unattended! The plastic only needs to be in contact with medium heat for a very short time (about a minute or less).
Figure 10. Heating the edges of a cut-open water bottle will make the plastic shrink, rounding the edges and making the bottle slightly smaller.
- Make sure you securely attach your different parts together. If you have difficulty with this, try wide duct tape and roughen the area where the tape needs to stick slightly with sandpaper before applying the tape.
- If you decide to add fins to your rocket, make sure your rocket will still fit the rocket launcher before attaching the fins to the bottle.
- If you decide to decorate your bottle rocket, remember to keep a "window" clear of any paint or decoration so you can still see the water level line created in step 4 of the Creating the Basic Bottle Rocket section.
Two rockets created by the Science Buddies team are shown in Figure 11. These performed well when tested against the requirements for your final product.
Figure 11.These rockets have been painted with spray paint, colored sand, decorative tape, and stickers. Note in the picture on the right, windows created by protecting the bottle with tape before painting are visible. The vertical window (green and partially covered with a space shuttle sticker) allows you to see the water level in the propulsion chamber. The top window (green and on the top right of the bottle) provides a view of the payload stored in the payload bay.
Checking the Prototype before Testing
Now, you are to evaluate if all four requirements for your final product are met before testing.
- Check if the propulsion chamber of your rocket is still a bottle that can be filled with water and still fits on your launcher.
- Verify if the payload bay of your rocket can be filled and emptied with sand. Weigh the amount of sand that fills up your rocket payload bay completely and verify if this is at least 200 g.
- Fill your rocket's payload bay up with sand. Note: This part can be messy, so be sure you are working in an area that can be cleaned up from any stray sand. Work over a trash can and use newspaper to protect your work surface.
- Zero out your scale so it indicates 0 g when the container you are using to measure (your measuring boat) is on the scale. Tip: If the scale you are using does not have a feature to zero it out, you will need to first weigh the measuring boat so that you can subtract this mass from the total when you weigh the sand.
- Transfer all the sand from the payload bay to the measuring boat. Tip: If not all the sand fits in your measuring boat, measure half of the sand, than measure the second half and add up the results.
- Read the mass from your scale. Tip: If the mass of the sand in your boat exceeds the capacity of your scale, measure half of the sand first, than measure the second half and add up the results.
- Record the mass of the maximum load in your lab notebook.
- You will need a test run to see if your rocket shoots off in a nice straight line until it reaches its highest point and tumbles back down. Proceed to the following section to perform this test and see if you are satisfied with your rocket.
If your rocket does not pass one or several of the four requirements for your final product, or you feel dissatisfied with your current rocket, fix any problems and further polish your design in a redesign phase until you are satisfied with the result.
You are all set to go outside, find a good location, and prepare for launching! Remember to take a gallon of water with you In case your location has no access to water. Note: The figures in this section are made with a basic bottle rocket. You will use your aerodynamic bottle rocket with payload bay for your tests.
- Find a launch area, which should be a clear space of 40 m (130 ft) long and 40 m wide.
- Search for a good launch location:
- The launcher should rest on a flat area.
- The ground should be soft so the U peg to secure the launcher can be pushed into the ground.
- Secure your launcher to the ground with the U peg, as indicated in the manual that came with the launcher. Figure 12 illustrates a well-secured launcher.
Figure 12. The launcher is held in place by a U peg going over the launcher and pushed into the ground.
- Fill the bottle rocket to the indicated water level with clean water.
- Put your rocket on the launcher. You will need to do this in a fast movement in order to spill only a little water. If this is too hard, you can also:
- Loosen the U peg so you can pick up the launcher,
- Place it upside down on the rocket, as shown in Figure 13, and
- Secure the launcher with the bottle to the ground with the U peg.
Figure 13. Placing the bottle rocket on the ground and pushing the launcher upside-down in the bottle spout allows you to attach the rocket without spilling any water.
- With your launcher back on the ground and secured, lay out your launch string.
- Attach the bicycle pump to the launcher.
- Add air to the bottle rocket by pumping until your pressure gauge indicates 30 psi (207 kPa).
- Clear the area of bystanders, and move away from the rocket launcher, out to the end of your launch string.
- Launch the rocket by giving a quick, but gentle, tug to the launch string.
- WOW! Did you see your rocket fly? If not, go to the FAQ section and perform a new test run as soon as you resolve the issue.
- Note that real rocket launches come with launch protocols, including a long list of safety checks. Write down a launch protocol for your launches in your lab notebook:
- Include all of the safety tips listed in the Caution section in your protocol.
- Once you start measuring the maximum height your rocket reaches, you will need a helper. As you create your protocol, include hand signals to inform one another to prepare for a launch, a failed launch, etc.
Learning How to Use the Altitude Finder
In this science project, you need to measure the maximum height your rocket reaches. With the altitude finder, you will measure the angle between a horizontal line and a line to the highest point on your rocket flight track, as shown in Figure 14. Figure 15 illustrates that the bigger this angle is, the higher your rocket went. Note that for this to be valid, it is important that the observer (the person holding the altitude finder) stays at a fixed distance from the launcher.
Figure 14. Person using the altitude finder to measure the height a rocket reaches. (Left) The rocket barely comes off the ground. (Middle) The rocket goes to medium height. (Right) The rocket goes very high. Note how the measured angles get bigger as the rocket goes higher. The angle between the arrows in red shows the measured angle, the angle between the altitude finder and the horizontal.
Figure 15. Higher points result in bigger measured angles. Note the observer is indicated by an orange dot in the figure.
Keeping the observer at a fixed distance from the launcher allows you to convert angles measured with the altitude finder (expressed in degrees) into heights (expressed in m). The math to do this is above the difficulty level of this science project, you can consult the Bibliography if you would like to get a glimpse of it. We have also included Table 1 to help you make the conversions. The table lists the height for an observer placed at 32 m from the object for angles 0 through 70.
|Angle (°)||Height (m)||Angle (°)||Height (m)||Angle (°)||Height (m)||Angle (°)||Height (m)|
Note that as the observer is placed closer to the launcher than what is advised on the altitude finder box, the height corresponding to an angle (e.g. 20° shows a height of 11.6 m) is much smaller than the height indicated on the altitude finder box (20° shows a height of 55 m).
You might wonder why the altitude finder only allows measurements between 0 and 70°. Readings above 70° would result in inaccurate measurements. In case your rocket does go higher, increase the distance between the observer and the bottle rocket launcher for all your measurements. Note that if you do so, you will no longer be able to use Table 1 to convert angles to height. Instead, you can use a graphical method, as explained in the Variations, or use your calculator, as explained in the document listed in the Bibliography, or ask a mathematics-savvy person to create a conversion table for you.
Now that you know the principle behind the altitude finder, let's see if it yields plausible measurements.
- Read the instructions on how to use the altitude finder, found on the box of the altitude finder. You will follow these instructions, except you will place yourself at a distance of 32 m (not at 152 m) from the launcher. This distance provides a good precision for the heights reached in this science project.
- Stand at 32 m or 105 ft (which is seven times the length of your launch string) from a relatively high object (e.g. a multistory house or a tall tree). Hint: Because the launch string of your bottle rocket launcher is 15 feet long, you can measure out a distance of 105 ft or 32 m by laying it out back-to-back seven times.
- Obtain a measure of the height of this object using the altitude finder.
- Point the altitude finder to the highest point of the object.
- Push the trigger of your altitude finder and wait until the swing arm hangs still before you release the trigger, freezing the swing.
- Read the angle indicated by the swing from your altitude finder. This angle is a measure of the height of the object.
- Use Table 1 to translate the angle into a height expressed in meters.
- Write down your measured angle and height in your lab notebook.
- Standing on the same observation spot, measure the height of part of this same object (e.g. the height of the first story or the trunk of the tree). Note that the distance between you, as observer, and the object has not changed.
- Repeat step 3 to obtain a measure of this height using the altitude finder.
- Write down your measured angle and height in your lab notebook.
- Ensure the measured height of your lower object (measured in step 6) is smaller than the measured angle of your higher object (measured in step 3).
- If your measurements seem incorrect:
- Make sure the distance between you as observer and the object you measure, is identical for both measurements. Remember, this distance should be 32 m. If it was not, retry placing yourself at the correct distance from the object.
- Make sure you used Table 1 to convert angles to meters, which is very different from the table listed on the altitude finder box.
- Retry, making sure to wait for the swing arm to hang still before you release the trigger, freezing the swing.
- Read the instructions that come with the altitude finder, especially the explanation on how to use the trigger and how to read the angle, making sure you follow the instructions.
- If all of the above fail, ask an adult to help you learn how to use the altitude finder.
Now that you have a functioning rocket, you can prepare the scientific test with a goal of finding out how adding a payload (quantified by its mass) influences the maximum height your rocket reaches.
- Copy the following table in your lab notebook; you will use it to record your measurements.
|Measured Angle (°)|
|Payload (% of maximum)||Payload
|Trial 1||Trial 2||Trial 3||Average||Average Height |
- Determine the masses of the loads you will use.
- Your goal is to do tests at 25%, 50%, 75%, and 100% of your maximum payload capacity.
- Look up the maximum payload you determined in the Creating an Aerodynamic Bottle Rocket with Payload Bay section. Note: Use 1 kg if your maximum was higher than 1 kg, as your bottle rocket might not be able to lift more mass.
- Fill in the values for "Payload (g)" in the second column based on the maximum payload. For example, if your maximum payload was 650 g, then 25% of your payload capacity is 0.25×650 g = 162.5 g. If your maximum was above 1 kg (1,000 g), you will use 25% (250 g); 50% (500 g); 75% (750 g), and 100% (1,000 g) of 1 kg.
- Create a measuring scoop equal to 25% of your maximum payload to make it easy to measure out 25%, 50%, 75%, and 100% of the maximum payload.
- Take a 500 mL empty transparent juice bottle. Clean out the bottle and let it dry. Remove the wrapper.
- Use your scale to measure the amount of sand making up a mass of 25% of your maximum payload (250 g if your maximum was over 1 kg). Consult the section Creating an Aerodynamic Bottle Rocket with Payload Bay for directions on how to use your scale.
- Use a dry funnel to transfer the sand you just weighed into your empty juice bottle.
- Put the bottle on a flat surface and shake the bottle a little so the sand is leveled.
- Use a permanent marker to draw the sand level on the bottle.
- Remove the sand from your bottle.
- Cut the bottle on the line you just drew and throw away the top. Be careful not to cut yourself.
- Round the edges of your cut-off bottle by heating them for a short time on a non-stick pan over medium heat, as described and shown in Figure 10. This step will help you avoid cutting yourself when you use your measuring scoop. Melting plastic bottles is easy, but should be approached cautiously. Ask an adult to supervise you for this step, and use the hood and fan, or a well-ventilated room, and never leave the bottle and stove unattended.
- You just created a measuring scoop that will help you measure the amount of sand in your payload bay for consecutive measurements. As you can see in Table 2, you will use no sand for your first measurement, 1 scoop for your second measurement, 2 for your third measurement, 3 for the fourth measurement, and 5 for your last measurement.
Ready to see how adding mass (a payload) will affect the height your rocket reaches?
Note: We suggest you do all the measurements in one sitting, so all measurements are taken under the same weather conditions. If you expect you will need to take a break, take measurements for all four payload masses for a trial in one sitting and perform measurements for the other trials at a later time.
Note: In case your location has no access to water, take about 4 gallons of water with you. Check the Materials list for other objects you need to bring.
- Go to the launch location and set up your rocket launcher. Read over the section Test Run to refresh your memory on all the details on how to find a good location and perform a launch.
- To find the spot for the observer, you need to find the direction at a right angle to the wind. You can skip this step if you can barely feel wind.
- Place yourself at the launch location, turning your body so the wind blows in your face.
- Stretch your arms out next to you so they form a straight line, as shown in Figure 16.
- Both arms point in a direction at a right angle to the wind. You will use these directions in step 3.
Figure 16. When the wind blows in your face, your stretched-out arms will point in directions at a right angle to the wind.
- Find the observation spot associated with this launch location:
Measure off 32 m, starting from the launch location in the direction at a right angle to the wind (choose one of the two directions in which the person's arms were pointed when stretched out), found in step 2. If you can barely feel wind, all directions are fine.
- Hint: As the launch string of your bottle rocket launcher is 15 feet long, laying it out back-to-back seven times allows you to measure off a distance of 105 ft or 32 m.
- Mark this spot with a heavy object, like your backpack or a filled bottle of water. This is the spot for the observer who will be using the altitude finder.
- Make sure the observer will not be looking into the sun as he or she follows the rocket. If he or she will be, pick up your heavy object and measure 32 m on the other side of your launch pad (the second direction you found in step 2).
- If, for any reason, you are not pleased with your observation spot, select a different launch location and determine the associated observation spot. Repeat this until you are satisfied with the launch location and observation spot.
- Inform your helper about the launch protocol you created in the Test Run section.
- Your first measurement will be for a zero mass of payload, in other words, an empty payload bay.
- Go through your launch protocol.
- Let the observer use the altitude finder to measure the angle corresponding to the maximum height the rocket reaches. See the section Learning How to Use the Altitude Finder if you need to refresh your memory on how to use the altitude finder.
- Write down the measured angle in your table like Table 2.
- Repeat steps 6–8 two more times for a total of three sets of measurements.
- Rub some petroleum jelly on the black ring of the launcher to keep it in good condition.
- Fill your payload bay with 1 scoop of sand, or 25% of your maximum payload. A second dry funnel will be useful to get the sand into the payload bay without spilling.
- Repeat steps 6–10.
- Add one more scoop of sand to your rocket payload bay for a total of 2 scoops, or 50%, of your maximum payload.
- Repeat steps 6–10.
- Add one more scoop of sand to your rocket payload bay for a total of 3 scoops, or 75% of your maximum payload.
- Repeat steps 6–10.
- Add a last scoop of sand to your rocket payload bay for a total of 4 scoops. Your payload bay is now filled with the maximum amount of payload you will use in your tests.
- Repeat steps 6–10.
Analyzing Your Data
- Calculate the average angle for each payload mass. Note that even though you might have chosen to convert each measurement to meters, you need to calculate the average of the measured angles and convert this average to a height expressed in meters.
- Start with the measurements for an empty payload bay. To calculate the average, first add up the measurements (the angles expressed in °) and divide the result by the number of measurements (3 in this case, as you performed 3 trials).
- Continue with the measurements for the heavier payloads (25%, 50%, 75%, and 100% of the maximum payload, respectively).
- Do not forget to record your calculated values in the table like Table 2.
- Convert your average measured angle to a height expressed in meters:
- Use Table 1 to look up the height corresponding to your average angles if the observer was placed at 32 m from the object.
- Note that if the distance of the observer to the launcher was not 32 m, Table 1 will not list the correct height. Instead, you can use a graphical method, as explained in the Variations to convert angles to height, or ask a mathematics-savvy person to create a conversion table for you.
- Record the height expressed in meters in your data table.
- Make a line graph of your average height data versus payload mass.
- Put the payload mass on the x-axis (the horizontal axis going across) and put the average height (in meters) on the y-axis (the vertical axis going up and down).
- Remember to clearly label the axes, add the units used, and add a clear title to your graph.
- Look at your data table, your graph, and your observations and try to draw conclusions from your results.
- Can you explain your results in terms of what happens as you add more payload in the bottle rocket? Think of what creates the upward motion of your rocket, which is explained in the Introduction. Hint: Watch the video in the Bibliography about Newton's laws. What happens when you increase the mass of an object, but keep the force pushing on it (in this case, the lift (reaction) generated by expelling water and air (action)— Newton's third law) the same?
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- Study how the pressure in the propulsion chamber of your bottle rocket influences the maximum height the rocket reaches as explained in Bottle Rocket Blast Off!.
- Study how the ratio of water to air in the propulsion chamber of your water bottle rocket influences the maximum height the rocket reaches. For example, you can make measurements with your bottle when it is 1/8 water, 1/4 water, 1/2 water, and 3/4 filled with water. Keep the pressure in your propulsion chamber constant for this study.
- As an addition to your science project, you can add a drawing to scale showing how the average measured angle corresponds to the rocket's maximum height. A brief description of what to do:
- Choose a horizontal on the lower end of your drawing.
- Place the observation spot and the launch location on the horizontal with the same number of units as the distance between the observer and the launch spot in your real-life test. For example, if in your test, your observer was at 23 m from the launcher, place 23 units between your observer and your launch location on your drawing. This way, you will have one unit distance on your drawing representing 1 m.
- Draw a vertical line through the launch location. You will measure the obtained maximum height on this line.
- Measure the average angles (the results of your test) with respect to the horizontal with a protractor placed at the observation spot. Figure 17, below, shows how to place the protractor to measure the angles.
- Draw lines at these angles, starting at the observer and through the vertical line from the launch location (the red, blue, and yellow lines in Figure 17). The location where this line crosses the vertical indicates the maximum height the rocket reached.
- You can measure the heights reached by the rockets on the vertical using your scale (one unit distance on your drawing equals 1 m.)
- Make sure to name the axes, and add a legend and a scale indication to your drawing. Not all of these are shown in Figure 17.
Figure 17. A scale drawing showing how the average measured angle relates to the attained height. The angle is measured with a protractor. Note the legend and scale are omitted in this graph.
Note you can find the mathematical formula linking distance, angle, and height in the Bibliography.
- Study the effect of adding wings or making your rocket more aerodynamic on the maximum height reached.
- Several simulators are available online, predicting the flight path of water bottle rockets. These simulators are computer programs calculating the flight path of a water bottle rocket using the laws of physics. Most of them allow you to change a number of parameters, like the volume of your bottle rocket, the pressure in your propulsion chamber, and others. Use a simulator to study the effect of changing one specific parameter, like adding a nose to a bottle rocket or changing the water versus air volume in your rocket. Then use your rocket to study the effect of changing the same parameter. Do you get the same relative improvement on the maximum height reached? Note that some simulators suggest values for the parameters. You can leave the suggested values for all parameters you do not know. NASA provides several Bottle rocket simulators. Others can be found online.
Frequently Asked Questions (FAQ)
- Check if you placed your bottle rocket properly on the launcher. The pictures in the section Creating the Basic Bottle Rocket can help you identify if the bottle is pushed down far enough and ensure the release latch is holding the bottle securely in place.
- Check if your bottle fits snugly on your launch tube. When your rocket is loaded with some water and placed on the launch tube, some water might trickle out. If water continues to stream out, see if rubbing the black ring with some petroleum jelly solves the issue. If the spout of your bottle is too wide, you might have to buy a new bottle.
- Ask an adult to remove the bottle from the launcher, following the instructions from the bottle rocket launcher manual.
- Rub some petroleum jelly on the black ring of your launch tube.
- Check if your bottle rocket fits the launcher. The pictures in the section
Creating the Basic Bottle Rocket can help you identify problems.
- Ensure your bottle fits snugly, but not extremely tightly, around the launch tube. If the spout of your bottle is too tight, you might have to buy a new bottle.
- The release latch should be able to grab the bottle as soon as some pressure is added to the bottle rocket. You can test this by putting an empty bottle rocket on the launch tube, pushing it completely down, and then pulling it back up. The bottle should come up a tiny bit, until the release latch stops it.
- The altitude finder allows measurements between 0 and 70°. Readings above 70° will result in inaccurate measurements. If your rocket does go higher, increase the distance between the observer and the bottle rocket launcher for all your measurements.
- Note that if you do change the distance between the observer and the launcher, you will no longer be able to use Table 1 to convert angles to height. Instead, you can use a graphical method, as explained in the Variations to convert angles to height, or ask a mathematics-savvy person to create a conversion table for you.
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