Turn your sound on, then press play.
A straw rocket has no engine. So what makes it go? You do. Your breath is the engine.
Your paper rocket is a tube with one closed end, called the nose. When you slide it onto a straw and blow, your air rushes up the straw and gets trapped inside the rocket. The air has nowhere to go, so it pushes hard on the closed nose. That push is a force called thrust. Thrust shoves the rocket off the straw. A harder puff makes more thrust.
Thrust only lasts for a tiny moment. As soon as the rocket leaves the straw, the push is over. After that the rocket is coasting, like a ball after it leaves your hand.
Gravity is a force that pulls everything toward the ground. It pulls on your rocket for the whole flight and never takes a break. That is why the path of the rocket curves down, like the shape of a rainbow.
Drag is air pushing back against anything that moves through it. Hold your hand flat in a strong wind and you can feel it. Drag slows your rocket down. A smooth rocket with a neat nose slips through the air with less drag. A crumpled, bumpy rocket has to fight a lot more air.
Here is a secret that many builders miss. If the nose has a hole, or the side of the tube has a gap, your air sneaks out instead of pushing. A leaky rocket barely moves. The tube also has to fit the straw just right. Too tight and it sticks. Too loose and the air escapes around the straw.
A system is a group of parts that work together. Your rocket is a system. The nose, the body, the fins, the weight, and your puff of air all have a job. Change one part and the whole flight changes. Keep an eye out for that as you go.
Fins are the little wings at the tail of a rocket. They do not push the rocket. Their job is to keep it pointing straight ahead.
Think about an arrow. The feathers at the back stop the arrow from tumbling. If the tail swings out to one side, the air pushes on the feathers and nudges the tail back in line. Rocket fins work the same way. Flying steady and straight like this is called stability.
A paper tube with no fins often wobbles, flips, or flies sideways. A sideways rocket hits a lot of air, so drag stops it fast.
Weight changes everything about a flight. The tricky part is that too little weight and too much weight both cause trouble.
Try to throw a cotton ball as hard as you can. It hardly goes anywhere. It is so light that drag stops it almost right away. A rocket that is too light has the same problem.
Your puff of air makes only a small amount of thrust. A heavy rocket is harder to speed up, so it leaves the straw slowly and drops to the floor quickly.
The best rocket is in the middle. It is heavy enough to punch through the air, and light enough for your puff to launch it fast. Engineers call this a trade-off. You give up a little of one thing to get more of another.
Where you put the weight matters just as much as how much you add. Weight belongs in the nose. A heavy nose leads the way, and the light tail with its fins follows behind, like a dart. If the tail is heavier than the nose, the rocket tries to flip so the heavy end goes first.
Easy ways to add nose weight: one small paper clip, a few extra wraps of tape, or a ball of clay the size of a pea. Add a little at a time and test after each change.
Lay your rocket across one finger and slide it until it stays level. That spot is the balance point. For a steady flight, the balance point should be closer to the nose than to the tail.
Add paper clips and watch the finger slide to the new balance point.
Engineers test their ideas before they build. In this lab you fly a pretend rocket. Change the settings, launch it, and see how far it goes.
The fair test rule: change only one thing at a time. If you change two things at once, you cannot tell which one made the difference.
Launch angle is how far up you tilt the straw. An angle of 0 is flat like a table. An angle of 90 points straight up at the ceiling.
No two puffs are exactly alike, so the same rocket can land in a slightly different spot each time. That is why engineers test more than once.
| Flight | Angle | Fins | Nose weight | Distance | How it flew |
|---|
No flights yet. Press the green button to launch.
The building steps open when every mission is finished. Here is what you still need to do:
You earned it. Go slowly and follow each step in order. Check the box when a step is done.
Use the ruler to draw a rectangle that is 2 inches wide and 5 inches long. Cut it out. Take your time, because straight edges make a smoother rocket.
Lay the pencil along one long edge of the strip. Roll the paper around the pencil to make a long, thin tube. Roll it snug, but not super tight. The tube needs to slide.
The seam is the edge where the paper ends. Run tape along the seam from one end of the tube to the other. Any gap is a leak, and leaks steal thrust. Then slide the tube off the pencil.
Slide the tube over your straw. It should slide on and off easily, with only a tiny bit of space around the straw. If it sticks, roll a new tube a little looser. If it is very loose, roll a new one a little tighter.
Pinch one end of the tube flat. Fold the top half inch over, like closing a bag of chips. Tape it down, and wrap the tape all the way around so no air can get out. Keep the tip rounded and soft.
Put the rocket on your straw and hold the rocket so it cannot fly off. Blow gently. If you feel or hear air sneaking out of the nose or the seam, add tape to that spot and test again.
Fold a small piece of paper in half. Cut out a triangle about 1 inch long. Because the paper is folded, you get two matching fins at once. Do it again so you have four. Use three fins or all four. You decide.
The tail is the open end. Tape each fin flat against the tube near the tail. Space the fins evenly. Three fins make a letter Y from the back. Four fins make a plus sign. Keep them flat and straight.
Tape one small paper clip flat against the nose, or wrap two or three more turns of tape around it. Now lay the rocket across one finger. The balance point should be closer to the nose than to the tail. If it is not, add a little more weight to the nose.
Every real rocket has a name. Write yours on the body with a marker. Now you are ready for the launch line.
Remember the fair test rule. Change only one thing between flights, and write down what you changed.
| Flight | What I changed | Feet |
|---|
| What happened | Why | Try this |
|---|---|---|
| It barely leaves the straw | Air is leaking, or the tube is too tight | Add tape to the nose and the seam. Check that the tube slides easily. |
| It flips or tumbles | The tail is too heavy, or the fins are too small | Add a little weight to the nose. Check your fins. |
| It curves to one side | The fins are uneven or bent | Flatten the fins and space them evenly. |
| It flies straight but lands close | It is too heavy, or the angle is off | Take off some weight. Try an angle in the middle. |
| It goes high and lands near your feet | The angle is too steep | Tilt the straw lower. |
Write three or more sentences. What did you change on your rocket? What happened? Why do you think it happened? Use at least two of these words: thrust, drag, gravity, fins, balance.
Big idea question: your rocket is a system. Which part changed the flight the most?
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