Pop Rockets
Rockets shoot skyward with massive amounts of thrust, produced by chemical reaction or air pressure. Scientists create the thrust force by shoving a lot of gas (either air itself, or the gas left over from the combustion of a propellant) out small exit nozzles.
According to the universal laws of motion, for every action, there is equal and opposite reaction. If flames shoot out of the rocket downwards, the rocket itself will soar upwards. It’s the same thing if you blow up a balloon and let it go—the air inside the balloon goes to the left, and the balloon zips off to the right (at least, initially, until the balloon neck turns into a thrust-vectored nozzle, but don’t be concerned about that just now).
A rocket has a few parts different from an airplane. One of the main differences is the absence of wings. Rockets utilize fins, which help steer the rocket, while airplanes use wings to generate lift. Rocket fins are more like the rudder of an airplane than the wings.
Another difference is the how rockets get their speed. Airplanes generate thrust from a rotating blade, whereas rockets get their movement by squeezing down a high-energy gaseous flow and squeezing it out a tiny exit hole.
If you’ve ever used a garden hose, you already know how to make the water stream out faster by placing your thumb over the end of the hose. You’re decreasing the amount of area the water has to exit the hose, but there’s still the same amount of water flowing out, so the water compensates by increasing its velocity. This is the secret to converging rocket nozzles—squeeze the flow down and out a small exit hole to increase velocity.
There comes a point, however, when you can’t get any more speed out of the gas, no matter how much you squeeze it down. This is called “choking” the flow. When you get to this point, the gas is traveling at the speed of sound (around 700 mph, or Mach 1). Scientists found that if they gradually un-squeeze the flow in this choked state, the flow speed actually continues to increase. This is how we get rockets to move at supersonic speeds or above Mach 1.
The image shown here is a real picture of an aircraft as it breaks the sound barrier. This aircraft is passing the speed at which sounds travel. The white cloud you see in the photo is related to the shock waves that are forming around the craft as it moves into supersonic speeds. Because the aircraft is moving through air, which is a gas, the gas can compress and results in a shock wave.
You can think of a shock wave as big pressure front. In this photo, the pressure is condensing water vapor in the air, hence the cloud. There are lots of things on earth that break the sound barrier – bullets and bullwhips, for example. The loud crack from a whip is the tip zipping faster than the speed of sound.
The rockets we’re about to build get their thrust by generating enough pressure and releasing that pressure very quickly. You will generate pressure both by pumping and by chemical reaction, which generates gaseous products. Let’s get started!
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We tried this with baking soda/vinegar & used a canister from Mini M&Ms. It made a nice loud pop and shot about 3 ft in the air. Going to try it with Alka-Seltzer tomorrow.
Thank you for saying you used M&M mini’s container. I would rather buy those than film. Especially now in the days of Digital Cameras.
Kelli Davis wrote: “just stopped in @ walmarts photo center…lots of fuji containers for the asking.”
Sounds great! See if you can land one on the roof
Anyone want to post their record heights?
This Sounds so Cool Me and My mom are going out side right now to try it!!!
Thanks!!
It was So Fun!! We loved it
we got one on the roof!! Also I went to Walgreen’s and there store brand film comes in the same canister as does Fugi, and I asked for help and was given all the old canisters that they had.
I don’t know our record heights as they went higher than the house. We lost one on the roof
. That was either the baking soda and lemon juice one or the alka-selter and lemon juice. Both went high into the air. We are waiting for dad to get home now so we can show him 
Thanks for making science so much fun
The sound for that video isn’t working on my computer. D:
How awesome!!! We just did the water so far, but a couple went higher than the roof! Kids and I were both so excited! Tried to video tape it, but it went so high, so fast I don’t think I ever got the top heights on tape. lol. Thanks so much! Can’t wait to do more tomorrow!! (How can you measure record heights??)
boys are ahving a great time. 16 yr old had-had to do it of his hand. now they are strapping it to a hot wheels car- our walmart doesn’t do inhouse film processing! wish i had known about the alternative mini m&m container!!!
boy will they get chores and summer school out of the way for this!!!
thanks aurora
what a beautiful name!!!
Try a different computer?
We just tried the rockets with alcohol (91%) and water, yet our “rocket” didn’t take off. We’re wondering why ?
We didn’t get any results using chalk/chalkdust and vinegar. Should we expect a different result ?
Eileen Wilkens wrote: “We didn’t get any results using chalk/chalkdust and vinegar. Should we expect a different result ?”
Great question! The chalk contains calcium, and the vinegar ‘eat’ its way slowly through it, producing tiny bubbles of carbon dioxide. (The calcium and acetic acid react to form CO2 and other stuff). I believe one student reported waiting two weeks before it generated enough gas pressure to blow the top off. This is an example of a SLOW chemical reaction, whereas the baking soda and vinegar is a FAST reaction. Did anyone try washing soda? (Just curious…)
Aurora
What a great day my 7 year old son has loved the rockets.
Is there a way to print out what you have wrote before each of the viedo’s with out the back area of the viedo?
Thanks
Eileen Wilkens wrote: “We just tried the rockets with alcohol (91%) and water, yet our “rocket” didn’t take off. We’re wondering why ?”
It sounds like you found out that alcohol and water does not produce a gas. Sounds good! Remember, you need a chemical reaction that generates enough gas pressure to pop the top off. Chalk and vinegar might, but the rate of reaction (the speed that the reaction moves along at) is so slow that it may not be a worthwhile way to propel rockets. Did you try hydrogen peroxide and potatoes? Or citric acid (in the pickling section) and vinegar? Baking soda? Baking POWDER?
Our FAST reaction
was about 20 feet high (alkaseltzer & vinegar). We used a wine bottle and tried putting a cork on, but the we couldn’t get the cork on fast enough and it exploded all over the helpers 
We tried the potatoes and peroxide today. Took about 5 minutes for it to build up enough gas to go up! (It was a very small lift off too. lol) Added the nose and fins – it didn’t go up as high, but came down much more gracefully.
Does surface area matter? Does it go higher if you shred, dice, or slice the potato? Crumble the effervescent tables, break into small pieces, or leave whole? How many tablets do you really need?
TAKING THE ROCKETRY PROJECT FURTHER…
You can also change the vehicle from just a rocket to a rocket car (glue two short straws parallel to each other cross-wise and insert a skewer into the straw with a film top at each end to make a wheel-axle assembly), or make a rocket glider (glue a straw lengthwise and thread onto fishing line, add wings), or strap three canisters together (can you get them to go off at the same time?) or a multi-stage rocket (stack three canisters, one on top of the other – you’ll need to glue the lid of one to the bottom of the next).
The record for a multi-stage is 46 feet.
CoWefa Lyda wrote: “What a great day my 7 year old son has loved the rockets. Is there a way to print out what you have wrote before each of the viedo’s with out the back area of the viedo? Thanks”
You can copy the text and paste it into a word document that you build for this class – that’s probably the easiest way of doing it for the summer. In fall, we’ll be having download-able workbooks so you can print them out and stick it in a binder.
I got the video working on my computer. This was really very fun to do!! I had a blast! =D
My son tried out a rocket airplane. It worked fairly well but sometimes there was a delayed reaction.
He tied the canister below a balsa flyer, at the center of gravity, and then threw the plane. The chemical reaction provided a nice boost, as long as the flyer didn’t land first!
We put in 2 tsp white vinegar in the 1st container and 2 tsp water in the other, and set them off at the same time. The one with the vinegar exploded first but the one with the water went higher. We also tried 2 kinds of milk: skim vs. 1 % : the skim was faster but the 1% went higher.
Jennifer Bosket wrote: “We put in 2 tsp white vinegar in the 1st container and 2 tsp water in the other, and set them off at the same time. The one with the vinegar exploded first but the one with the water went higher. We also tried 2 kinds of milk: skim vs. 1 % : the skim was faster but the 1% went higher.”
Wow – cool! Does temperature of your liquids matter?
Isaac Close wrote: “worked well, we managed to get three launches from one tablet!!
It was awesome. One of my rockets shot up higher than our roof, however, it fell into our back pond!
Darrien Davis wrote: “I just wanted to share that me and best friend beat the record of 100 ft. with the slingshot. We mesured and the final results were 127 feet, 9 inches!!! We are now going to experiment with 8 1/2 in by 14 in. Maybe we can make it more aero-dynamic.”
I think the Pop Rocket was a great experiment. I tried it with water, alcohol, and some kind of solution that was really hard to spell. Water worked the best.
Has any one tried it with a kodak film canister instead of a fuji? Did you compare the results?
We tried the rocket with alcohol and the vinegar/baking soda tablet. It just sat there and didn’t do anything. Does anyone know why?
Veronica Cable wrote: “We tried the rocket with alcohol and the vinegar/baking soda tablet. It just sat there and didn’t do anything. Does anyone know why?”
It sounds like you found out that the tablet dissolves (is soluble) in water, but not alcohol. In chemistry, we make solutions (dissolving solid bits in liquids) so that the surface area of the molecules are fully exposed to each other to chemically react. When you put the tablet in the water, it exposes more of the molecules on the surface of the tablet to each other, which is why the bubbles appear on the surface. It sounds like the tablet is not soluble in alcohol. A lot of solids are soluble in either alcohol or water, but not both. Does that help?
We drilled a small hole in the lid, used modeling clay as a plug, and secured the lid to the canister with duct tape after filling it with 1 tbsp water and 1 effervesent tablet. We thought that restricting the exit area would increase velocity and height but it just pushed out the plug and streamed out in an arch under the lid and lifted off about 2 inches. We all had a good laugh and it was subsequently dubbed (by 3 boys) as the whizzing rocket! Shouldn’t this have worked as anticipated?
We loved the pop rockets. My soon to be ten year old is having a birthday party and we are going to do them. We found foamy rockets at the craft store and are going to hot glue them to the bottom of the canister. Can’t wait to see how they fly tomorrow!
Will let you know.
BTW, have you seen the you-tube video about diet coke and mentos? Now there is a propellant! We tried it but the mentos came out of the package and we couldn’t get the lid on fast enough, so we had a towering fountain of coke.
Clavonne Holter wrote: …have you seen the you-tube video about diet coke and mentos? Now there is a propellant! We tried it but the mentos came out of the package and we couldn’t get the lid on fast enough, so we had a towering fountain of coke.”
Yes, that’s a great one! The mint-flavored coating on the candy reacts with the stuff in soda to release all the CO2 bubbles at once, and your bottle shape resembles a rocket (big to small diameter increases the speed of the soda as it exits). You can get the same result by placing soda in an ultrasonic jewelry cleaner – the vibrations will knock the CO2 bubbles out all at the same time as well, producing a soda geyser! This is a FAST chemical reaction, so you’ll need to get creative about how to get the top on (which is why the jewelry cleaner may work better, because you can start and stop the reaction when you want to). Happy Experimenting!!
Eilkeen Wilkens wrote: Our FAST reaction was about 20 feet high (alkaseltzer & vinegar). We used a wine bottle and tried putting a cork on, but the we couldn’t get the cork on fast enough and it exploded all over the helpers.
Sounds really fun.
Rate this experiment: I rate it 10/10 because it is really fun and has a lot of different solutions. By the way, Aurora thank you very much for answering the question about the alcohol and tablet. Sound like you took a lot of time with it.
Just tried it with baking soda/vinegar. The baking soda just covered the alkaseltzer tablet, and then there was a lot of vinegar. The pop rocket exploded so high that I couldn’t find it again afterwards! Amazing experiment!
My friend and I tried this experiment with alcohol, hydrogen peroxide, vinegar, baking soda, and an alkaseltzer tablet. It went so high. (my friend wanted me to say it blew up our neighbor’s tree; however, it didn’t.)