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7 hours ago, Saltface said:

I don’t understand your trebuchet. Why was your throwing arm being stretched?

Centrifugal force. Mostly from the weight of the arm itself.

Edited by MattR
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On June 1, 2019 at 2:04 AM, Saltface said:


..I don’t understand your trebuchet. Why was your throwing arm being stretched?


23 hours ago, MattR said:

Centrifugal force. Mostly from the weight of the arm itself.

Not working the physics out in full, but if it is the typical design, 100 lbs on the beam 12" from the fulcrum is 100 foot-pounds of torque to begin with. That's a lot of potential energy on an arm that's about to rotate from over minus 100 degrees to 0 (straight up and down). By the time the arm is at minus 45 degrees, it is pulling the mass off its line and it needs far more force than the weight of the mass to do so. Meanwhile on the opposite end of the beam, a sling is being launched -- lighter weight, but longer path -- almost the opposite trajectory. The whole point of the beam is to transfer the kinetic energy of the descending mass to the ascending sling. So in an efficient engine there reaches a critical angle where the fulcrum is largely irrelevant and all of the inertia of the mass is at its maximum and in opposition to the inertia of the sling, and the energy to change the trajectory of each is along the length of the beam. It goes from dropping one object to lift the other to trying to pull these objects together.

The exact amount of force along the beam at that point depends on the total length of the throwing arm, the length of the sling, the mass of the projectile,  the mass of the materials, and the energy lost to friction in all the moving parts (which can be somewhat offset, as ancient tapestries indicate, by mounting the device on rollers). It is quite reasonable to assume that, in @MattR's model, 50,000 pounds of force could be a minimum.

And that is why we trigger a trebuchet from a distance. You would want to do the same for a catapult, but for different reasons.

Edited by qwazse
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  • 3 months later...

Update Oct 2, 2019:

The family of a 13-year-old boy who was injured in the left eye by a catapulted potato during an overnight troop camping outing in Santa Clarita in 2017 agreed to settle a lawsuit brought on the boy's behalf against the Boy Scouts of America for $90,000.

Los Angeles Superior Court Judge Laura Seigle is scheduled to decide Friday whether to approve the settlement, which will leave the Valencia boy with about $59,300 after his medical expenses, attorneys' fees and other costs are paid.

During a Sept. 20 hearing, the judge asked for some additional documentation from the plaintiff. She also said the money the boy will receive must be placed in a blocked account and that all withdrawals will need court approval.

According to the suit filed May 30, Boy Scout Troop 499, operated by the Western Los Angeles County Council and sponsored by the Greater Santa Clarita Optimist Club, had an overnight camping event, dubbed the Troop 499 Zombie Overnighter, at Hart Park in Santa Clarita on Nov. 4. 2017.

Several activities were planned for the scouts and for the Cub Scout Webelos who were invited to attend and all of the events were under the guidance of a scoutmaster, who was in charge of the troop's activities and the safety of the scouts, according to the lawsuit.

One activity planned for the overnighter was the catapulting of potatoes using a makeshift slingshot, according to the suit.

The troop's scoutmaster, who was in charge of coordinating the event and was responsible for making sure it was conducted safely, failed to take reasonable steps to protect the scouts, such as obtaining protective eyewear and the plaintiff was struck by a potato in the left eye as a result, the suit alleged.

The suit alleged "the plaintiff suffered, and continues to suffer from physical and emotional injuries, including disfigurement."


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