Unit 2: Lesson 2. Balloon Racers. This lab is broken up into two parts, first let's begin with a single stage balloon rocket:

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1 Balloon Racers Introduction: We re going to experiment with Newton s Third law by blowing up balloons and letting them rocket, race, and zoom all over the place. When you first blow up a balloon, you re pressurizing the inside of the balloon by adding more air (from your lungs) into the balloon. Because the balloon is made of stretchy rubber (like a rubber band), the balloon wants to snap back into the smallest shape possible as soon as it gets the chance (which usually happens when the air escapes through the nozzle area). And you know what happens next the air inside the balloon flows in one direction while the balloon zips off in the other. Question: why does the balloon race all over the room? The answer is because of something called thrust vectoring, which means you can change the course of the balloon by angling the nozzle around. Think of the kick you d feel if you tried to angle around a fire hose operating at full blast. That kick is what propels balloons and fighter aircraft into their aerobatic tricks. Materials: Balloons String Two straws Timer Ruler Procedure: This lab is broken up into two parts, first let's begin with a single stage balloon rocket: 1. Blow up the balloon (don t tie it) 2. Let it go. 3. Wheeeee! 4. Tie one end of the string to a chair. 5. Blow up the balloon (don t tie it). 6. Tape a straw to it so that one open end of the straw is facing the front of the balloon and the other is facing the nozzle of the balloon Supercharged Science Page 1

2 7. Thread the string through the straw and pull the string tight across your room, making sure to hold it as horizontal as possible. 8. Let go. With a little bit of work (unless you got it the first time) you should be able to get the balloon to shoot about ten feet along the string. You've now made what's called a single stage rocket. A single stage rocket has, well, a single stage where all the fuel (or air pressure) is released constantly until there's none left. Let's take some measurements and find out about how fast the single stage rocket travels. Grab your stopwatch, and set up your rocket. Start the timer exactly when you release the balloon. Stop the timer when it stops moving along the string. Finally, measure how far along the string the rocket traveled. Do three trials, and fill out the table below: Trial # Time (seconds) Distance Traveled (meters) Average Speed (m/s) Once you've filled out the table for your measured time and distance, calculate the average speed of the single stage rocket using the following kinematic equation: velocity = distance / time Fill out the last column in the table with your corresponding calculated values. Single stage rockets are fun and all, but multi-stage rockets are even cooler. A multi-stage rocket will use all the fuel in one tank, ditch it, then use all the fuel in the next tank. Rocket design can get very complicated (it is, after all, rocket science), but the purpose behind multi-stage rockets is higher efficiency. There's something called the thrust-to-weight ratio that describes how much thrust (or air pressure in our case) a rocket has compared to how heavy the rocket is. Imagine a very heavy rocket with very little thrust, it has a small thrustto-weight ratio. Now imagine a beach chair strapped to a huge rocket engine. It will have a very high thrust-toweight ratio. The rocket fuel itself adds to the weight of the rocket because the fuel goes along for the ride too. A multistage rocket will have multiple engines all firing at once, but using different fuel tanks. Once the fuel in a tank is empty, the engine wont produce any more thrust, so it's just useless weight (and these things are heavy), so they get ditched. For example, NASA's space shuttle, has a multi-stage launch system. Once the smaller tanks on the outside are depleted, they are detached and fall back to Earth Supercharged Science Page 2

3 We're not going to build a space shuttle, but we can still built a multi-stage balloon rocket. Watch the video on how to create a multi-stage balloon rocket. An extra set of hands can be useful in this next part. Measure the same parameters as before (time and distance traveled) for the multi-stage rocket, and fill out the table below: Trial # Time (seconds) Distance Traveled (meters) Average Speed (m/s) Once you've filled out the table for three trials, calculate the average speed for the multi-stage rocket using the same kinematic equation as before. Remember this is the total average speed. The rocket will travel slower during the first stage, because of its thrust-to-weight ratio. It has one balloon's thrust pushing the whole system. In the second stage, there will be the same amount of thrust, but only pushing one balloon. Compare your results and see which balloon moved faster and farther Supercharged Science Page 3

4 Problems: 1. How fast would a rocket accelerate if it reached mph from rest in only 5 seconds? 2. How high above the ground would the rocket be after the 5 seconds of acceleration? 3. Imagine the rocket was a single stage rocket, and after 5 seconds, it ran out of fuel. What would be the maximum height that the rocket would reach? 2014 Supercharged Science Page 4

5 Answers: m/s m m 2014 Supercharged Science Page 5