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!
For this experiment, you will need:
I didn’t have any Alka-Seltzer, so I thought what the heck I will try backing soda and vinegar. First time trying it, it worked like a charm, it scared me because I wasn’t expecting it to work so well. It made me giggle like it made you giggle. So much fun!
We tried the pop rockets and some of the canister lids didn’t close too well. The stuff leaked out. With the ones that closed well, they went really high–about 10-15 feet high. One of them landed on the roof and another landed in a neighbor’s yard. We also used M&M mini containers and those only went about 1-2 inches high. If you don’t know where to find the film canisters, ask Walgreens. It was FUN! We’re planning to show our Dad tonight.
I’ve sent you a private message… look for it! 🙂
We couldn’t find the film canisters, so we bought the mini M&M containers. That didn’t give them much lift, about 5 inches. Next we tried baking soda and vinegar. It didn’t do much better, only about 4-6 inches. 🙁
I’m Denise’s son Ethan and my friend and I took a water bottle, put baking soda and vinigar in, and put a cork on it and we shot the cork REALLY far! We also tried varying baking soda, vinigar, and different bottles to get different results.
hi my name iis hannah deborah’s daughter. i love this experiment!
My favorite part of this experiement is watching Aurora laugh when the rocket goes off. 🙂
Very good! It’s kind of the opposite of what you might think, isn’t it? Science is sooo much fun that way…
with experience I figured out that the more water you don’t put in the higher it goes.
We tried it with Alka Seltzer and water and it worked great. We got 2-3 pops out of each tablet. The kids liked it so much we had to try it with vinegar and baking soda because we ran out of Alka Seltzer (buy the BIG box if you do this…the kids will want to do it over and over again!). The vinegar was great, too. By the end, we had three girls covered in exploded vinegar and baking soda!! They did this for an hour! Very fun. Thank you!
From Sophie: why does vinegar and baking soda work?
Lisa Fox- Try attaching the lid to something, a piece of cardboard, a shoebox, whatever. Then the lid will stay still and the car will go forward. Good Luck! 🙂
We made a rocket with 1/2 of a paper towel tube. Use 4 film canisters w/water & effervescent tab in each film canister. It did not go up in the air. but the lids did blow off of each film canister. The first time we used the whole length of the paper towel tub. We thought it did not lift off because it was too heavy. But after we cut it in half it still did not lift off. We did put a fin on each side of the base of paper towel tube.
We did lay to paper towel on the side and mounted it to Lego wheels, but it do not move on the floor. All four film canister blew the lids off.
We will try the bathtub to see if it will move with film canister on the water.
I was gonna say that theres room for it to build up but i forgot to write it in. This is jonathan
Yes – you’ve got it! Not only ‘time’ but also space – that gas has got to go somewhere, and if you have a pocket of space for it to cram together and build up pressure, off it goes with a BANG!
It goes higher with less water. Cause theres more time for the pressure to build up.
Hi my name is Lucas and I’m 9. I tried 2 tablets,less water,and turned it upside down. It was awesome!
Interesting… you still have your eyebrows I assume? CO2 is invisible to the eye, so I am assuming you saw bubbles?
You probably want to check out the generating O2 experiment in Unit 15 if you want to test gases with a match – I show you how to detect hydrogen and oxygen with this method.
Our film canister had a bad seal on it so it didn’t work very well, but after we opened the can I thought I saw carbon dioxide. So my brother lit a match and we barely stuck it in the container where we thought the Co2 was and the match went poof! no more (lit) match!
Euell Beard
hi im Caeden and im 11 years old
i have not tried it yet but SUPER exited to i will let know how it goes=)!!!!!!!!
You need something that generates a lot of gas quickly… and tuns doesn’t do that. Baking soda and vinegar do, though.
can I use tums?
how about three tablets!!! :3
We LOVED this Experiment! My kids Beg me to buy more Alka-Seltzer so they can watch the canister shoot way up in the sky. Out of all the Experiments, this is their favorite so far. Thanks Aurora!
You’ll be able to do this soon – we did it with 200 kids in Alaska in January… I am sure you can find a way. 🙂
I forgot to add my name to my email. I am 9 and my name is Kade.
If it were not winter, then I would be able to do this.
BLASTED WINTER!!!!!!!!
Of course I want to do this in January/2012…….sigh
Hi! I’m Abby! (10 years old) I did not have ANY items needed for this easy experiment! It was AGONY watching you have all the fun so I got thinking. You said in the video that those alka seltzer pills were made from baking soda and vinegar. Well, that got me thinking even more. I asked mom for some baking soda and vinegar. She showed me where they were. I told her what you had said about the pills. Well, she was PRETTY enthusiastic about me wanting to do an experiment so, apparently she said, “yes”. Well JACKPOT! It subsituted very nicely! Thank you so much Aurora, for teaching me that science is SO much more than long boring hours of writing,reading,and staring at a textbook!
Thanks Again!
I will have a whole new perspective of science from now on!
Abby
Oh P.S. We almost landed it on the roof once we got the alka seltzers pills!
Cailey, I just thought of something. Since the lids go farther than the lego car, why not try to shoot the lids out as a cannon! Maybe you can make a game out of it! Try it! In fact, I will try it too.
Andrew
We had a lot of fun with this today and we were able to get three uses per tablet!
We couldn’t find a canister for our pop rocket, so we are going to try a Wallgreens medicene canister. Since our family gets their medicene from Wallgreens, all we have to do is wait until another canister is empty. We will also ask Wallgreens if they have any empty canisters that they don’t need.
Subject: A great project
such a cool idea just popped into my head! I have not tested it yet.
items needed: 2 chairs with back rests, 1 straw, 1 balloon, strong string/rope etc., tape, and materials used for the pop rocket above.
step 1 set the two chairs backrests facing each other about 7 feet apart.
step 2 put the straw on the string.
step 3 tie the string from one chair to the other.
step 4 blow your balloon up, tie it off, and tape it to the straw.
step 5 put a long enough strip of tape to go around the pop rocket capsule and stay attached to the balloon.
step 6 before you tape on the pop rocket activate it (put water into the film capsule put in the Alka-Seltzer) as quick as possible tape the pop rocket to the balloon and step back.
let me know how it works out!
— Liam 7th grader
You need to make your vehicle as low-friction as possible – which means it needs to roll easily and be lightweight (like the film lid). Legos tend to be heavy and have a lot of friction in the wheels, so what about strapping this rocket to a piece of foam and floating it in the bathtub tonight? Water makes a good low-friction environment.
Make sure to send me a picture to post!
If you really want to strap this to your vehicle, then increase the size of your container (or number of containers) and the amount of effervescents used.
Aurora: Can you help with modification for a pop rocket mobile? Daughter Tori, 6, built a lego vehicle, attached the film canister and of course the lid travels a great distance but the vehicle barely moves. Max distance achieved has been about 6 inches. She made it as light as possible, larger wheels are better, used a slight incline, smooth concrete. Dad tried to modify further but, alas he found Tori’s modifications to be the best of all. :):) Go Girl!!
He even tried to place it on the hood of our car.
We suspect a pin hole in the lid will not solve our physic’s problem.
Suggestions?
Hi! It’s Cailey!
We didn’t have any film or M&M canisters so I used a LOT of different things.
Here are a few of them: A small Wyler’s Light container, a balloon, and a little ziplock bag.
The container blasted about 6′, the balloon just kept on expanding but the baggie was an awesome surprise!
Tomorrow we are buying M&M’s (Yum!) to try that canister to see how high we can get it!
Anyway, it was fun!
what if that hit a light in the video it sound like is made a hole in the roof :-/
Try it and let me know how it goes!
Could you uses soda and mentos for the rocket instead?
Hi I am Abigael Melanie’s daughter, and I’m eleven. This experiment was AWSOME! At first we tried it in the house, bad idea I know. When we tried it ourselves I put the water and the tablet into the canister too slowly. So when I finally put the lid on the canister it exploded from under my hand! Of couse it left a big mess on my desk in our school room. After doing this same thing twice I realized I needed to do everything faster and do it outside. When I did just that it worked better than I expected, my brother sister and I were ocuppied for about two hours until we nearly ran out of alka-seltzters. So my family really enjoyed this experiment just as I did. THANKS!
it was soooooooooooo much fun!! we tried it a and if you put less water it will shoot up farthere.
You’ll need to find a place that still develops film and ask for their recycling bin. You can also use the ideas suggested here int he comment section including the M&M containers or plastic bottle with a cork.
where can i get a film canester in stores?
Your web browser has a bookmark option – create a section for e-Science and organize them under that index for quick access. Or simply write down the name on a post-it so you can enter it in the search box and find it super-quick. I have several post-its on my computer monitor frame.
so cool but i wish there was a way to book mark the experaments you like.
Hi Aurora,
I’m Jill’s daughter. My name is Greta and I’m 6.
I thought it was really cool! it went about 15 feet up.
This is my big sister’s science program but I like it too.
This is my first experiment.
-Greta
If you go to any costco or Sams film area..Just ask if they have any film canisters for a science project..Costco gave us a huge bag of film canisters for my boys.
We tried to find film canisters, and could not, since most people have gone to digital. I tried the clear plastic viles that came with our Diamond package, and they leaked a little when turned upside down. After a couple tries, they did launch, but two of the three plastic viles cracked when they hit the kitchen floor (tile). I recommend others try it outside if they want to preserve the viles!
Yes, this was from the Aeronautics DVD that had dozens of projects on it – most of which are located now in the Flight Lab of e-Camp. 🙂
that seems like its a cut from a longer video, is it? but not from one as long as the Science Fair Rocketry Project video,
thanks again, Brannon, 12
\
What kind of info are you looking for? Is there a specific question I can answer for you? I did post information on how to turn this experiment into a full-blown Science Fair Rocketry Project, complete with a very long step-by-step instructional video, written report, and guidebook.
is there a video with more info?
thanks, Brannon
Cool
I said his not Jan Secord (above)
Hmmm… since alka-seltzer is pretty concentrated stuff and you’re only supposed to drink the solution (not the tablet) when you use it as medicine, I would recommend trying the mentos-coke combination in your mouth instead (only don’t swallow it or you’ll get serious digestive problems).
Aurora, you need to try the experiment in your mouth!(with out the film cannister) And see how long you can ceep the stuff in there with your mouth closed! It is SO fun!
Try using only a SMALL amount of water (like about a quarter-full) and then the tablet… does that help? And yes, baking soda and vinegar is a great variation.
It wouldn’t work for us using the water and Alka Seltzer tablet. Going to try baking soda and vinegar.
This is such a good laugh!! After a little kitchen search the eldest came with the magnificant idear to use those tablets for tired feet ;)) We decorated each our own little container with some colour and some mousetraps etc.(yep, girls will be girls ;))) Mum taped a little lego-man on top and of he went.
A quarter of a tablet is good for 4 of 5 blasts. The less water, the better and higher he will go.
Okay, we are going to use baking powder now…..see if lego-man will go even higher this time.
A fantastic time had by both boys (9 and 10)! They started experimenting right away to discover whether more or less water worked best–then when they found the answer, proceeded to come up with a theory why. Next they put a Lego man on top of the rocket to zip him into space–they got him quite a bit higher than the house!
Then they tried gluing foam wings on the sides; one got blasted off, but then they liked it better since the canister spun round as it came back to earth. They stopped only because we ran out of AlkaSelzter!
Hello Aurora and everybody! This is a great blog to read. Great to hear the ideas, experiments, and way to get film containers. Thinking, I couldn’t get film containers I was on the lookout for something to do for our big family. At Sam’s club recently they were selling this zipfizz drink powder. So,after using the powder, that is the container my husband tried with about a quarter of the alka seltzer tablet and water. It was fantastic ! One of my sons helped him and said it went higher with less water and more air, if I understood him correctly. Storming this morning, so hopefully this afternoon all the children get to do theirs. (forgot about the m&m containers) thanks so much! Love your enthusiasim! Hope every mom finds their enthusiastic thing to share in life!
I have tried this experiment this is aosome
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.)
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!
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.
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.
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!!
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.
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?
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 tried the rocket with alcohol and the vinegar/baking soda tablet. It just sat there and didn’t do anything. Does anyone know why?
Has any one tried it with a kodak film canister instead of a fuji? Did you compare the results?
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.
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.”
It was awesome. One of my rockets shot up higher than our roof, however, it fell into our back pond!
Isaac Close wrote: “worked well, we managed to get three launches from one tablet!!
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?
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.
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!
I got the video working on my computer. This was really very fun to do!! I had a blast! =D
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.
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.
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?
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.
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 🙂
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?
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 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…)
We didn’t get any results using chalk/chalkdust and vinegar. Should we expect a different result ?
We just tried the rockets with alcohol (91%) and water, yet our “rocket” didn’t take off. We’re wondering why ?
Try a different computer?
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!!!
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??)
The sound for that video isn’t working on my computer. D:
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
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.
It was So Fun!! We loved it
This Sounds so Cool Me and My mom are going out side right now to try it!!!
Thanks!!
Sounds great! See if you can land one on the roof 🙂 Anyone want to post their record heights?
Kelli Davis wrote: “just stopped in @ walmarts photo center…lots of fuji containers for the asking.”
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.
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.