Rockets Describe space explorations and the understandings gained from them including: Technologies used to explore space.

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1 Rockets Overview In this exercise, students learn how to build a simple rocket fueled by an effervescent antacid tablet in water. They will explore adjusting variables (e.g., tube size, amount of water, amount of fuel). They will then undertake a challenge to build a commercial rocket that must reach a certain height, carrying a payload, while trying to make a profit. North Carolina Standard Course of Study 5.04 Describe space explorations and the understandings gained from them including: Technologies used to explore space. Textbook References McDougal Littell The concepts are addressed in Unit E, Space Science, in Chapter 1.3, Spacecraft help us explore beyond Earth, pp Prentice Hall The concepts are addressed in Chapter 8, Exploring Space, Section 8.1, The Science of Rockets, pp This activity replaces activities on p 260 and on pp Background Rockets are launched when a gas is emitted rapidly in one direction, causing the rocket itself to move in the opposite direction. For every action (the force of the escaping gas), there is an equal and opposite reaction (the thrust causing the rocket flight). The main factors that influence this action-reaction are the mass of the rocket (including its payload), the amount of gas produced, and the time it takes for that gas to be released. In addition, the aerodynamics of the rocket itself can influence its flight a nosecone for streamlining, fins for stability, etc. In the first part of this exercise, students can get a feel for the influence of these factors. They may learn the underlying physics in a later course. When the National Aeronautics and Space Administration (NASA) sends up a rocket, the scientists not only have to obey the laws of physics, they also have to work within a budget. Private companies also send rockets into space, placing satellites for telecommunications, for example. In the second part of this exercise, students must meet a challenge while trying to keep costs down and make a profit. Their rockets must carry a payload and reach a height of 3 meters. They must keep track of expenses (fuel, the rocket itself, the number of launch attempts) and income (generated by the payload the rocket carries). During Part 1, students may explore their rockets freely at no cost. However, in Part 2, they must pay for each launch attempt. The more attempts, the greater the cost. On the other hand, the greater the payload, the greater the profit. Thus,

2 students must choose between a lighter payload that is more likely to succeed versus a heavier payload that may not reach its destination. Materials Materials for the whole class Launching platforms. (The round platforms provided with the kit are sized so that if a rocket tips over before taking off, it will hit the rim of the platform rather than shooting at a person.) Flat surface outdoors, at least 10 meters from obstructions (for example, a parking lot or athletic field). Assorted plastic tubes 2 diameters (1 and 1 1/4 ) and 2 lengths (5, 7 ). Assorted protective plastic caps (matched to tube diameters). Assorted rubber stoppers (matched to tube diameters). Pieces of vinyl tubing (for payload). Effervescent antacid tablets. Water. A scale for weighing materials, fuel, payloads, etc. Materials for small groups 1 graduated cylinder (10 ml). Materials for individual students 1 pair of safety goggles. Science notebook. Preparation Find an open area outdoors that may be used for launch sites. It should have a flat surface and be clear of obstructions for at least 10 meters. Observers should stand 3-4 meters from the launch. Parking lots or athletic fields are good examples. Several launching platforms can be set up, if they are far enough apart so that students won t be in each others way and safety won t be compromised. For Part 2, mark a line 3 meters from the ground on a wall or post that students can refer to for meeting the challenge. A standard basketball hoop could work as well since, at 10 feet, it is only about 3 inches higher than 3 meters. Procedure for Part 1 Demonstrate one rocket launch. o Put a plastic cap over the closed end of a tube. o Add 5 ml of water. o Holding the tube at an angle as shown in the left side of Figure 1 (not drawn to scale), insert one half of an effervescent antacid tablet just inside the mouth of the tube so that it doesn t come in contact with the water.

3 o Insert a rubber stopper tightly. o Quickly turn the tube rocket stopper-side down and stand it up on the launch pad as in the right side of Figure 1. o Stand back and watch the fun! Explain safety procedures: o Students must wear safety goggles. o Rockets must have their protective caps in place. o Launches may only be made one at a time from the designated launching platforms. o Observers must stand 3-4 meters from the launching platforms. Advise students that they have the rest of the class period to launch rockets. Tell them that they may explore freely, trying different diameters and lengths of tubes, different amounts of water, and different amounts of fuel. Also tell them that during the next class period they will be given a challenge to carry a payload up to a minimum of 3 meters. They should keep notebook records of their trials during this class period to help them make their design decisions for the challenge. Distribute materials to student groups. You might want to limit the number of tablets. A half tablet is actually more than enough. Tubes, caps and stoppers can be available ad lib, so that groups can choose which ones they want to try. Suggestions for teaching with inquiry: o Do not give detailed specific instructions at first. Simply do the demonstration launch slowly enough for observant students to get a feel for the process. For example, it is important that the stopper be firmly seated in the tube. Otherwise, the gas will leak out. Let the students discover this for themselves. o Also, the narrower tubes work better than the wider ones. This is a surprise to students, but worth discovering on their own. Many students will choose the largest tubes, fill them with lots of water, and add a whole fuel tablet. The result is a rocket that wastes a lot of energy (see Reflection/Discussion section below). Sometimes, less is better.

4 o If students are having difficulty getting a successful launch, feed them small hints, a bit at a time. Do not touch their rockets; the students should do all the manipulations themselves. Allow time at the end of class for clean-up and to present the following challenge for the next class period. You will provide more details of the challenge during the next class period. By presenting the challenge now, you will give students more time to think about what they may want to try. Design a rocket that will carry a payload to a minimum of 3 meters. Since this is a commercial enterprise, you will want to make a profit. You will have to pay for materials, fuel, and launch fees. You will earn money from your clients for your payload if you are successful. Procedure for Part 2 Present the following challenge (there is a student handout at the end of this lesson): Design a rocket that will carry a payload to a minimum of 3 meters. Since this is a commercial enterprise, you will want to make a profit. You will have to pay for materials, fuel, and launch fees. You will earn money from your clients for your payload if you are successful. Here is a list of materials costs: Rocket body (one-time fee unless changes are made for later launches; includes fins, nosecone, etc.) Protective cap (one-time fee unless changes are made for later launches) Stopper (one-time fee unless changes are made for later launches) 3,500, , , Water (per milliliter) 1, Effervescent tablets (per gram) 20, Launch fee (per launch) 250, And here s how much your customers are willing to pay for your services: Service charge (one-time fee for first launch only) 3,000, Payload (per gram) 400, The price structure has been set so that most students will make a small profit if they take a conservative approach modest use of fuel, modest payload, etc. Here is a sample balance sheet for one launch:

5 Item Unit Price # of Units for 1 Launch Cost Rocket body (one-time fee) 3,500, ,500, Protective cap (one-time fee) 50, , Stopper (one-time fee) 100, , Water (per milliliter) 1, , Effervescent tablets (per gram) 20, , Launch fee (per launch) 250, , Total cost 3,935, Service charge (one-time fee) 3,000, ,000, Payload (per gram) 400, ,400, Total income 4,400, Profit (or loss) 465, If students are not successful on their first attempt, they can still make a small profit after a second identical launch. In this case, they only have to pay for the additional fuel and a second launch fee. All other costs and incomes are the same. Item Unit Price # of Units for 2 Identical Launches Cost Rocket body (one-time fee) 3,500, ,500, Protective cap (one-time fee) 50, , Stopper (one-time fee) 100, , Water (per milliliter) 1, , Effervescent tablets (per gram) 20, , Launch fee (per launch) 250, , Total cost 4,220, Service charge (one-time fee) 3,000, ,000, Payload (per gram) 400, ,400, Total income 4,400, Profit (or loss) 180, Students can make a bigger profit if they are willing to risk taking on a larger payload. This might require several launch attempts (greater expense), but eventual success could reap larger profits. Before launch, students should design and present a balance sheet similar to the ones above. They will need to weigh their tablets and payloads and measure the amount of water they will use with a graduated cylinder. These balance sheets could be kept in their science notebooks along with any records of observations

6 they make during the trials. Reflection/Discussion When the tablet mixes with the water, the gas produced is carbon dioxide (CO 2 ). As the CO 2 expands rapidly, pressure builds up inside the tube. This force pushes against the stopper (and the water sitting on top of the stopper) and eventually the stopper pops out. According to Newton s third law of motion, for every action there is an equal and opposite reaction. The action of the popping stopper has to be balanced by the reaction of the rocket tube moving in the opposite direction. So the rocket shoots up into the air. There are many factors that influence the flight of the rocket. For example, the energy of the expanding CO 2 does not all get used just to push the stopper out. Unfortunately, some of that energy gets lost in the form of heat. The water heats up, the stopper hits up, the tube heats up, and there is the friction of all these materials rubbing against each other. Thus, the amount of water used plays a role in the final result. If there is not enough water, not much CO 2 is generated, and the rocket doesn t go very far. If too much water is used, a lot of the energy produced by the expanding gas goes into heating up all that water instead of just pushing on the stopper. Again, the rocket doesn t go very far. But if the right amount of water is used, a lot of gas is produced and not much energy is wasted as heat. The rocket flies high! Another factor is the volume of air at the beginning of the reaction. As the CO 2 is produced, the pressure builds up until the stopper pops. Then the volume of air plus CO 2 increases rapidly and the pressure decreases just as rapidly. If the air space doubles, the pressure decreases by half. Therefore, if the rocket starts with a small air space, this doubling of volume occurs almost immediately, and the pressure decreases so rapidly that there is little force left to push the rocket upwards. On the other hand, if the rocket starts with a large air space, the decrease in pressure takes longer and the force available to push the rocket is greater for a longer period of time. The rocket flies high! Assessment After the challenge attempts have been completed, students should turn in a final report that will include a sketch of their rocket, their balance sheet(s), the amount of profit (or loss), and an explanation of their success or failure.

7 Rocket Challenge Design a rocket that will carry a payload to a minimum of 3 meters. Since this is a commercial enterprise, you will want to make a profit. You will have to pay for materials, fuel, and launch fees. You will earn money from your clients for your payload if you are successful. Here is a list of materials costs: Rocket body (one-time fee unless changes are made for later launches; includes fins, nosecone, etc.) Protective cap (one-time fee unless changes are made for later launches) Stopper (one-time fee unless changes are made for later launches) 3,500, , , Water (per milliliter) 1, Effervescent tablets (per gram) 20, Launch fee (per launch) 250, And here s how much your customers are willing to pay for your services: Service charge (one-time fee for first launch only) 3,000, Payload (per gram) 400,000.00