To put it my way, catapults throw, trebuchets fling. A catapult launches its projectile somewhat like throwing something that is cupped in your hand with a straight arm. A trebuchet is more like holding a string attached to an object, and swinging your arm up and letting go of the string. Also a trebuchet uses a large weight to move the arm, the catapult is more like having a spring. This was probably kind of confusing, but I hope I was able to help :)
-Catapults are any DEVICE that launches projectiles, or throws an object.
-Trebuchet are A TYPE of catapult, using gravity or (with counterweight) or traction (men pulling down on a rubber band) to launch projectiles or objects.
A catapult uses tension to launch projectiles, while a trebuchet utilizes gravitational potential energy from a counterweight. Catapults are typically smaller and less accurate for long distances, whereas trebuchets are larger and designed for greater distance and accuracy. Historically, both were used in warfare, with catapults being used earlier and trebuchets becoming prominent in the Middle Ages.
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