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Help with the physics of a Catapult

  1. Aug 27, 2016 #1
    So currently i am working on a robot, and i have gone to my physics teacher on how to help me achieve what i want out of it but she was not detailed with her explanation. It is only her second year teaching physics so i don't blame her but this seemed like a good place to put it.

    So this is for a competition called VEX robotics, i figured that could matter to any who wants to understand why i am asking but since it is a physics question i cam here. So currently my machine throws about 4 feet high but only 2 feet across. I just want to know is the physics behind designing a catapult so that i can figure out what can be accomplished to get more horizontal distance and a little less vertical distance. My Physics teacher said to look at the angle on the piece where the object sits, is this true and what should i look at? Please include any formulas because i do not understand where the angle comes into play. here is a picture when the machine is in the thrown position for reference, when it is down the outstretched c channel is parallel to the ground.
  2. jcsd
  3. Aug 27, 2016 #2


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    Read up on projectile motion. The launch angle and velocity alter the range. Max range is typically achieved at a 45 degree launch angle if the launch point and target area are at the same height.
  4. Aug 27, 2016 #3
    Ok thank you! But which angle should i be working to achieve 45? should it be the one that the object will be thrown on or the stop angle of the arm?
  5. Aug 28, 2016 #4


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    Change whatsoever you need so that the actual projectile launches at 45 degrees. You may need to change both of the angles you mention but I would start with the angle at which the arm stops.

    Check that centrifugal force can't cause the projectile to slip out early as that will send it up at a steeper angle. Eg use a cup or similar on the arm to hold the projectile.
  6. Aug 28, 2016 #5

    jack action

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    The equations: Projectile motion

    The initial angle is the one when the projectile will leave the cup of your catapult, so usually when the arm will stop. As @CWatters said, this is assuming the projectile doesn't slide on the catapult as it moves up. In that case, you have to add the sliding velocity (as a vector) to the arm velocity to find the net velocity of the projectile and its true angle.
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