A sample of ruby processing

angle.rb

require 'pp'

class Pendulum

  def initialize(x, y, r)
    @origin = PVector.new(x, y)
    @r = r
    @angle = Math::PI / 4
    @a_velocity = 0.0
    @a_acceleration = 0.0
    @damping = 0.995
  end

  def update
    gravity = 0.4
    @a_acceleration = (-1.0 * gravity / @r) * Math.sin(@angle)
    @a_velocity += @a_acceleration
    @angle += @a_velocity
    @a_velocity *= @damping
  end

  def display
    x = @r * Math.sin(@angle) + @origin.x
    y = @r * Math.cos(@angle) + @origin.y
    stroke(0)
    line(@origin.x, @origin.y, x, y)
    fill(175)
    ellipse(x, y, 16, 16)
  end
end

def setup
  size(640,360)
  @pendulum = Pendulum.new(width/2, 10, 125)
end

def draw
  background(255)

  @pendulum.update
  @pendulum.display
end

# try this 
require 'pp'
load_library :vecmath

class Pendulum

  def initialize(x, y, r)
    @origin = Vec2D.new(x, y)
    @r = r
    @angle = Math::PI / 4
    @a_velocity = 0.0
    @a_acceleration = 0.0
    @damping = 0.995
  end

  def update
    gravity = 0.4
    @a_acceleration = (-1.0 * gravity / @r) * Math.sin(@angle)
    @a_velocity += @a_acceleration
    @angle += @a_velocity
    @a_velocity *= @damping
  end

  def display
    x = @r * Math.sin(@angle) + @origin.x
    y = @r * Math.cos(@angle) + @origin.y
    stroke(0)
    line(@origin.x, @origin.y, x, y)
    fill(175)
    ellipse(x, y, 16, 16)
  end
end

def setup
  size(640,360)
  @pendulum = Pendulum.new(width/2, 10, 125)
end

def draw
  background(255)

  @pendulum.update
  @pendulum.display
end