Engineering III: Trebuchets Design & Force Analysis

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Discussion Overview

The discussion revolves around the design and force analysis of trebuchets, specifically comparing two methods of arm motion: allowing the arm to swing freely versus stopping it at a certain point to release the projectile. Participants explore the implications of these methods on the force exerted during the launch and the resulting projectile velocity.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant questions whether a freely swinging arm or a stopping point would produce more force when launching a projectile.
  • Another participant suggests graphing the velocity of the projectile for both options and notes that the shape of the projectile holder could influence the results.
  • A participant, who has not yet taken physics, speculates that a stopping block could provide equal or greater force, depending on its placement and the arm's exertion of force at that point.
  • One participant explains that the force from the arm accelerates the projectile and varies throughout the arm's motion, depending on the driving mechanism.
  • There is mention of the basic kinematic equations and the relationship between mass and acceleration (F=ma) in the context of the trebuchet's operation.
  • A participant clarifies that the driving mechanism involves a weight and a sling, raising questions about how the force produced by the sling relates to the throwing arm's output.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness of the two methods of arm motion, with no consensus reached on which method would yield better results in terms of force and projectile velocity.

Contextual Notes

Some participants note the need for further understanding of physics concepts and equations, indicating that the discussion may involve assumptions about the participants' knowledge levels and the complexity of the physics involved.

chrisjj
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For my Engineering III class we're designing trebuchets.

But, specifically, my question is:

If I have the arm swing forward and let it go as it does normally, where it swings through and then relaxes back to a 90 degree position, will there be more force present in throwing the object there; or option B: would there be more throwing force if I had an immediate stopping point along the axle where the throwing arm would hit into stopping the swing at the right point for the sling to release the object I'm throwing?
 
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What are your thoughts on this? Graph the velocity of the projectile for the two different options and see what you get. And keep in mind that the shape of the projectile holder will have an effect on your answer.

My guess is that there is a tradeoff in launch velocity and accuracy for the trebuchet design tradeoff that you are exploring...

BTW, homework and coursework questions should normally be posted in the Homework Help forums here on the PF, but more complex project work can sometimes be posted in the general forums. I'll leave your thread here for now.

Welcome to the PF, BTW.
 
berkeman said:
What are your thoughts on this? Graph the velocity of the projectile for the two different options and see what you get. And keep in mind that the shape of the projectile holder will have an effect on your answer.

My guess is that there is a tradeoff in launch velocity and accuracy for the trebuchet design tradeoff that you are exploring...

BTW, homework and coursework questions should normally be posted in the Homework Help forums here on the PF, but more complex project work can sometimes be posted in the general forums. I'll leave your thread here for now.

Welcome to the PF, BTW.


I haven't taken any kind of physics class yet, being I'm only in eleventh grade and physics is next year. So, I'm not sure where to begin on any of that. If you wouldn't mind, could you get me started, if not just the equations needed.

But just from a guess, I would think that there would be either the same if not more force with having a stopping block, as long as it's located at a point that the throwing arm isn't exerting any more force and that the stopping block will add excess force to that amount.

Sorry about wrong section, didn't notice the Homework/Coursework area before hand. And thank you.


Thanks for response!
 
chrisjj said:
But just from a guess, I would think that there would be either the same if not more force with having a stopping block, as long as it's located at a point that the throwing arm isn't exerting any more force and that the stopping block will add excess force to that amount.

I'd say that's a good guess. The force from the arm is what accelerates the projectile, according to the classic equation F=ma (m is the mass of the object). The force will vary through the arm motion, and depend on what your driving mechanism is (elastic band, or whatever).

If there is no more force from the arm to the projectile, then it is not accelerating anymore, so stopping the arm there does no harm.

The basic equations of motion are the "kinematic" equations:

http://en.wikipedia.org/wiki/Kinematic

You can understand the basics without calculus, but they will make more sense after you take some calculus and physics next year.
 
berkeman said:
I'd say that's a good guess. The force from the arm is what accelerates the projectile, according to the classic equation F=ma (m is the mass of the object). The force will vary through the arm motion, and depend on what your driving mechanism is (elastic band, or whatever).

If there is no more force from the arm to the projectile, then it is not accelerating anymore, so stopping the arm there does no harm.

The basic equations of motion are the "kinematic" equations:

http://en.wikipedia.org/wiki/Kinematic

You can understand the basics without calculus, but they will make more sense after you take some calculus and physics next year.


The driving mechanism is just a 6 lbs. weight. So, the throwing arm is driven by the weight. But then there is a sling included as well -- attached to the end of the throwing arm. The sling is then driven by the throwing arm, which is driven by the weight, correct? So the force produced by the sling and put onto the projectile is relative to the throwing arms output of force... or is it just dealing with the sling?
 

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