Catapult Lab
The popsicle stick catapult is one of the most built projects in school science. The class measures how far the pom-pom went. Nobody can see why: how much of the push the pom-pom got, how much the air took, or why the angle everyone was told is best never is. Catapult Lab builds the same catapult on a bench, throws in slow motion beside the arc it would fly with no air, shows where the energy went, and prints the build so the class can test a real one against it.
Using this with a class? Make a free class and add your students yourself: each gets a username and password, with no email or Google account needed. Or give them one join code. Using Google Classroom? Post the link there; with a free class, the link also puts each student in your class, so you see their work. mytekDev is also available from the Google Workspace Marketplace, so your school's Google admin can install it for everyone.A first lesson: One period: build the classic catapult, throw a pom-pom and read the two arcs, swap the heavy bottle cap for a paper cupcake liner, add bands until the stick snaps, find the best angle, then print the build, make a real one and type its throws into the app.
Set up a free class Share to Google ClassroomWhat a student actually does
Seven craft sticks, some rubber bands and a bottle cap lie on a table. The student builds the catapult most classes build in five steps, the way it is put together for real: five sticks stacked and banded, two sticks banded at one end, the stack pushed in between them, the cap glued on. A pom-pom goes in the cap. They drag the cap down until it sits on the base and let go. The throw plays in slow motion, high and back over the banded end, and lands at 0.39 m on a tape measure. A dashed arc beside it, the same throw with no air, lands at 0.65 m. The card shows where the energy went: about a tenth of it to the pom-pom, two thirds still swinging the heavy cap and the stick, a quarter turned into heat in the bands.
Then they change one thing at a time. A paper cupcake liner instead of the bottle cap sends the same pom-pom about 0.78 m, and the guide asks why. More sticks in the stack tilt the arm and throw lower and farther: 1.48 m with nine. Four bands at the banded end store more, and a full press snaps the stick at about 21 mm, drawn broken. A spoon catapult on an axle has a cross-bar that sets the launch angle exactly: with one band and the bar at 45 degrees a pom-pom goes 1.19 m, and at 30 degrees about 1.59 m. Every different build is its own version in the throws table, so throws from before a change are never mixed with throws after it.
Find the best angle runs the same throw at every setting and draws the chart. Print the build gives one page with the catapult drawn at real size, a 100 mm ruler to check the printer, the parts, the steps, a cut-out press gauge and a safety box. The class builds it, throws it five times, and types the distances under Your real one: the app works out how much less energy the real one gives the throw, and the next drawings of that build are tuned to it. Six challenges, a sheet with questions per grade, and a Setup for the teacher round it out.
Find the best angle throws the same pom-pom from every stack, each pressed to the base. A stacked catapult throws high, back over its banded end, and cannot throw lower than 66 degrees, so 45 is not even on the menu. The spoon catapult's cross-bar can reach 45, and its best is lower still, about 25 degrees with one band: a stop closer to upright gives the bands a longer pull, so the throw leaves faster.
What they are learning while they work
Nothing here is presented as a lesson. This is what the activity is made of.
| What the student does | What it is |
|---|---|
| Swaps the bottle cap for a paper liner and watches the same pom-pom go twice as far | Energy transfer. The bands give back what was stored, and the arm, the cup and the pom-pom all have to move. A heavy cup on a light pom-pom keeps most of the push for itself. |
| Reads the solid arc against the dashed no-air arc for a pom-pom and a ping pong ball | Air resistance. A fluffy pom-pom is slowed by the air about as hard as gravity pulls it at launch, so its path is lopsided, not a neat arch. A heavier ball loses less. |
| Runs Find the best angle and sees the best is not 45 degrees | Launch angle and range. 45 degrees is only best with no air, a throw from floor level and the same speed at every angle. A real catapult breaks all three. |
| Reads Effort, Fulcrum and Load under the catapult | Levers trade force for speed. The stacked catapult is a first-class lever during the throw, the spoon a third-class one. In both, the cup end moves much farther and faster than the bands. |
| Adds bands until a full press snaps the stick | Stored elastic energy, and limits. A stiffer catapult stores more for the same press, and bends the stick harder. The stick gives out long before the bands do. |
| Changes one thing at a time and compares versions in the throws table | A fair test. When two things change at once, the guide says you cannot tell which one did it. |
| Builds the real one from the printed sheet and types in its throws | A model and the real thing. The drawing lands the same every time; a real one will not. The gap between them is data about the real build: the bands, the glue, the hand. |
How to tell whether it landed
Ask, and let them show you. A student who has understood it can answer these without help.
- Why did the same pom-pom go farther from a paper liner than from a bottle cap?
- What is the dashed arc, and why does a pom-pom fall so far short of it?
- Your best angle was not 45 degrees. Give two reasons.
- Where are the effort, the fulcrum and the load on your catapult?
- Why did adding bands make it throw farther, and then break?
- Your real catapult did not land where the drawing did. What might explain the difference?
Use it in your subject
Not a technology class? Then the app is how students show what they learned in your unit. More projects for every subject.
Middle school engineering
MS-ETS1-4 most of all: "Develop a model to generate data for iterative testing and modification of a proposed object, tool, or process such that an optimal design can be achieved." The app is that model, and the printed build is the object. MS-ETS1-1 to 3 for criteria, comparing designs and combining what worked.
Middle school physical science
MS-PS3-5 for energy moving from the bands to the arm to the pom-pom and the air, shown as shares with no energy calculations, inside its boundary. MS-PS3-1 for a heavier projectile against a lighter one. No NGSS performance expectation at any grade includes the two-dimensional arc itself, so the arc is enrichment, not a standard the app claims.
Grades 3 to 5
3-5-ETS1-1 to 3 for the classic catapult challenge, 4-PS3-4 for a device that uses stored energy to cause motion, and 4-PS3-1 for faster meaning more energy. The grades 4 and 5 level uses centimeters and words, with no numbers on the energy.
High school
HS-PS3-3 for a device that converts energy, judged by its output for a given input: the high school level shows millijoules stored, given back and given to the projectile, and the launch speed. State physics and AP Physics 1 projectile work, and quadratics in Algebra 1, for the arc.
Practical notes
- AgesGrades 6 to 8 are the home ground. A grades 4 and 5 level uses centimeters and words. A high school level adds the launch speed and angle and the energy in millijoules.
- TimeOne period for the classic catapult, the cup swap, the snap and the best angle. A second to build the real one from the printed sheet and compare.
- EquipmentA computer or Chromebook with a modern browser. Nothing to install. For the real one: craft sticks, #33 rubber bands, bottle caps, glue, pom-poms, and eye protection for everyone, building too.
- CostFree. The app has no paid tier.
- PrepAbout ten minutes: throw the default catapult, swap to the paper liner, add four bands and press until it snaps, run Find the best angle, and print the build once to check your printer prints at 100%.
- In a groupOpen Setup in the app's header: which questions are on the sheet, questions of your own, and whether students may tune the drawing to their real catapult.
For co-ops, microschools, and classrooms
Set it up once in Setup and hand the project out as the starter; the setup travels with it. Every throw on the screen is exact, so two students with the same build and the same press get the same distance, and the class can compare builds side by side. Their real catapults will not agree, and that is the second half of the lesson. The sheet asks four questions written for each grade level, and Hand in needs every one answered.
Common questions
Is it free?
Yes. Catapult Lab has no paid tier, and it can be tried right on this page without an account.
Does it replace building a real catapult?
No. Pair them. Print the build, make the real one, and type its throws under Your real one. The app works out how much less of the push the real one gives the throw and tunes its next drawings of that build to it.
How real are the numbers?
The sticks are standard craft sticks (114 by 9.5 by 2 mm, about 1.3 g) with the stiffness and strength of birch. The projectiles are a 1 inch pom-pom, a mini marshmallow and a 2.7 g ping pong ball, with air drag that grows with the square of the speed. The flight checks out against published cases, including a trebuchet field test. Two numbers are estimates still to be measured: how hard the bands at the banded end hold it down, and how much of the stored energy comes back. Real bands and sticks differ from bag to bag, so a real catapult can land well short of the drawing or past it, and the speeds and energies are given as "about".
Why is the best angle not 45 degrees?
45 degrees is only best when there is no air, the throw starts at floor level, and the speed is the same at every angle. A stacked catapult cannot throw lower than about 66 degrees at all. On the spoon catapult a stop closer to upright gives the bands a longer pull, so the throw leaves faster at a lower angle: with one band the best stop is about 25 degrees, with air or without. Find the best angle shows which reason matters for the build in front of it.
Is it safe to build the real one?
With care. The printed sheet says it: eye protection the whole time, light soft things only (pom-poms, marshmallows, ping pong balls, never coins, marbles, pencils or stones), aim at a target on the floor and never at a person, check the bands for nicks, and press slowly because a stick can snap and splinter.
What does it simplify?
The throw is side on, so nothing drifts left or right. The stick does not whip past its rest shape, the base does not slide on the table, the projectile does not spin, and there is no wind. The stacked catapult's stack sits 40 mm from the banded end and the cup 10 mm from the free end. Grades 4 and 5 do not see the lever labels.
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Where to go next
Start with Catapult Lab
Trying it costs nothing and takes about five minutes. An account is what makes the work last.
Catapult Lab is one of the making apps on the platform. The swing and the flight run at a fixed step of a fraction of a millisecond, so a throw lands in the same place on a fast laptop and a slow Chromebook, and the app's test suite checks that.
Page last reviewed November 2026.
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