Valentine’s Day LEGO Hearts Catapult

Valentine’s Day is almost here, and we love this STEM challenge that not only has us playing with physics, but also engineering with LEGO. This Valentine’s Day LEGO Hearts Catapult is a STEM challenge perfect for elementary aged kids, and makes a great classroom party game!


Lego Hearts and Candy Hearts Catapult Challenge

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We LOVE a good catapult build. Once the kids have mastered the basic popsicle stick catapult build, it opens the doors to all sorts of new challenges and games. With Valentine’s Day coming up, plus it being Heart Month, it only made sense for us to create a hearts themed catapult STEM game.

The best part is the giggles and laughs and pure joy on the kids faces when they play with a game they created from scratch. Nothing is better than that feeling of accomplishment and fun!


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For this challenge you will need to gather up a few simple supplies.

Hearts Catapult LEGO Supplies

For the Heart

LEGO – we used all red bricks, but you can use whatever you have available. Don’t have LEGO? Make your heart out of other materials like wood blocks, pipe cleaners, tinker toys, or even other popsicle sticks. You could even make one out of paper and hang it. Let the kids get creative!

For the Catapult

Jumbo Popsicle Sticks (aka craft sticks)
Bottle cap
Candies or little plastic hearts for launching


Building the Popsicle Stick Catapult

To save on time, start by engineering the catapult. This will allow time for the glue to dry while you are building the heart.

To build your catapult, grab 10 jumbo popsicle sticks. You can do this with regular sized, but we prefer our jumbo ones.

Take 8 of the popsicle sticks and stack them up. We used red plus plain wood because we didn’t have enough red to do the entire catapult in red.

Secure each end of the stack with an elastic.

Now take the remaining two popsicle sticks and stack them. Secure one end with an elastic.

Glue the bottle cap on the opposite end from the elastic. Leave a little gap from the end of the popsicle stick so you have a small handle for launching.

While the glue is drying, build your LEGO Heart.

Building the LEGO Heart

In this project the heart is our target and the goal is to shoot candies or mini hearts through the centre of the heart.

This was such a fun part of this project. The kids loved digging through their LEGO bins and find all the red bricks. Then came the puzzling out of how they wanted to build their heart. I let the kids take the lead on this and build it the way they wanted.

One discovery they made was that it worked the best if they started in the middle at the top, then built up and out, creating a mirror image. If they didn’t copy each side, brick by brick, things got a little wonky and the heart structure became unstable.

I let them learn by trial and error, their hearts breaking a few times, until they came up with a structure that they were happy with, and was stable.

LEGO Heart

PRO TIP! – The catapult launches quite high, so depending on your space, you might want to raise the heart up a bit by adding a platform.

If you don’t have LEGO, build a heart out of pipe cleaners, tinker toys, wood blocks, or even cut one out of paper and hang it. All you need is a heart shaped target, get creative and build it with what you have available.

Finishing the Catapult

By the time your heart is built, the glue should be dry. If it isn’t, give it a bit more time. It needs to be dry or it will come apart when you try to launch.

To finish assembling your catapult, take your stack and between the bottom two popsicle sticks. wiggle the bottom popsicle stick from your 2 stack between them. This will open up your two sticks so they form a V. Now secure it with an elastic.

You are now ready to play!

LEGO Hearts Catapult Challenge

Playing Hearts Catapult

Set up the LEGO heart, then position your catapult. Load it with a candy, then aim and LAUNCH!

Challenge your students to play with the physics by adjusting the way they use the catapult to change the force.

Study the arc to see if they can calculate exactly where the catapult needs to be to get the candy right through the middle of the heart.

Measure the distances of the catapult launches to see if variations in the projectiles, designs or builds makes a difference.

The Science Behind a Catapult

Catapults are a timeless and popular activity for a reason. They are fun, but they also teach some wonderful STEM lessons.

In this activity we are hitting three pillars of STEM: Science (Physics), Engineering and Math.

And like most STEM activities, this project can be easily adapted to a variety of ages.


Students are challenged to build their engineering knowledge in two ways with this project. First, by figuring out how to build a LEGO Heart target that is able to stand up and stable.

Second, by building their catapult to ensure maximum launch to shoot those candies far!


Simple math measurements can be used for younger kids, but with older students have them work out the percent gain based on design differences. Maybe moving the perpendicular sticks 1 cm on the stack (fulcrum) gives a 10% gain on the distance of the shots. Have students work out these calculations.

They can also measure the angle and see if they can find the best angle for their catapult design. Hint: there is a perfect angle, it’s 45 degrees.

Science (Physics)

All the science here is focused on our friend Newton and his laws. Newton’s Third Law of Motion states:

An object at rest stays at rest until a force is applied, and an object will stay in motion until something creates an imbalance in the motion. Every action causes a reaction.

Isaac Newton

When we pull down on the catapult we are building up potential energy. You can feel it wanting to GO! Students will discover that they need to use a hand or finger to hold the bottom stick of the catapult stable while launching. This is due to all of that potential energy that is built up when you press down on the catapult before launching.

Release the catapult and all of that potential energy changes to kinetic energy and your candy hearts go flying towards your LEGO Heart target! But there is one more thing at work here, and that’s gravity which causes the projectile to move in an arc, eventually falling to the ground.

Older kids can dig deeper with more advanced physics lessons. Discuss concepts such as fulcrum, force, stored (potential) energy, kinetic energy, payload and even the angle of the launch platform to see which angle provides the best flight of the heart candies. Students can study the work of Galileo on parabola, the relationship between the horizontal and vertical trajectory when a projectile is launched.

Most of all, make the month of Hearts and Valentine’s a month to build a love of Science, STEM and Learning!

LEGO and Candy Hearts Catapult Challenge


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