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Medieval fantasy has enjoyed a rabid cult following for decades, inspiring and captivating people across all interests — gamers, role players, actors, filmmakers, storytellers, designers and artists. Chalk it up to the popularity of J. R. R. Tolkien’s “Lord of the Rings” series.

But perhaps the era calls up one ideal vision of society, where each villager specializes in a craft or trade — haberdasher, bookbinder, blacksmith — that contributes to daily life. Or maybe we love the magical thinking of King Arthur and his court.

At any rate, we also latch on to tales with a good battle, where bravery meets handcrafted and sometimes ingenious weaponry.

The simple machinery of some of these weapons can teach you a thing or two about physics. For some hands-on learning that’s also fun, go back a few centuries for your next LEGO Bricks project. Build the castle walls, forge your weapons and play with transferred energy!

Catapult: Design and build a machine from LEGO Bricks that can launch marshmallows (or your payload of choice) into your target. How does it work? When the arm of the catapult stops, the marshmallow is released, and there, you see a transfer of energy, from arm to airborne marshmallow.

Trebuchet: Now that you’ve played with the catapult, it’s time to build and test a variation. Compared to the catapult, a trebuchet is a complex machine, relatively speaking, as counterweight and swinging arm move together to launch the payload to its target. These can be even more engaging to design and build, because even a few tweaks can alter the outcome. It’s no wonder there are trebuchet competitions.

A trebuchet incorporates physics concepts such as velocity, arc and gravity. Ideas and models abound online, including here and here. Start building and let the siege begin!

How do the two compare? As this physics blog points out, a trebuchet and catapult use transferred energy a bit differently. For example, the arm of the catapult reaches a high speed when it launches the projectile, which means wasted energy.

Test the two and explore how they make different results. Is one more accurate than the other? Which situations are best suited for a catapult, and when would you want to use a trebuchet?