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Homework Help: Check calculation on pendulum.

  1. Dec 26, 2009 #1
    Can someone check my calculation for pendulum. Its written in C++, but I think it should be understandable.

    //F = mg*sin(theta) = ma;
    //a = F/ m
    //a = mgsin(theta) / m
    //a = g*sin(theta)
    ball.accelVec = Vector3D( g * sin( changeInAngle ) ,g * cos(changeInAngle) , 0.0f );

    //V = v_0 + a*t
    ball.velVec += ball.accelVec * deltaTime;

    // X = v*dt + 1/2 a*dt^2
    ball.posVec += ball.velVec * deltaTime + 1.0f/2.0f * ball.accelVec * deltaTime * deltaTime;

    changeInAngle = atan2( ball.posVec.getY(), ball.posVec.getX() ) - restAngle;

    rope.setEndPoint( ball.posVec );
    Basically, ball.accelVec is the critical one, since everything else depends upon it.
    The Vector3D is Vector3D( x ,y z ). So is the acceleration vector correct for the pendulum.

    I think the Force for the pendulum should be < w*sin(theta), w*cos(theta) >, where w is
    weight and theta is in radians ?

    Sorry for the programming language.
  2. jcsd
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