Class: RubyLabs::SphereLab::Body

Inherits:
Object
  • Object
show all
Defined in:
lib/spherelab.rb

Overview

Body

A Body object represents the state of a celestial body. A body has mass (a scalar), position (a vector), and velocity (a vector). A third vector, named force, is used when calculating forces acting on a body. The size and color attributes are used by the visualization methods.

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(*args) ⇒ Body

Create a new Body object. If the argument list is empty, the attributes (mass, position, etc) are all set to 0. Otherwise the arguments should be mass (a Float), position (a vector), and velocity (another vector). A fourth argument is an optional name for the body.

Example:

>> b = Body.new
=> : 0 kg (0,0,0) (0,0,0)
>> b = Body.new(1e6, Vector.new(0,0,0), Vector.new(0,0,0), "test")
=> test: 1e+06 kg (0,0,0) (0,0,0)



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# File 'lib/spherelab.rb', line 206

def initialize(*args)
  if args.length > 0
    @mass, @position, @velocity, @name = args
  else
    @mass = 0.0
    @position = Vector.new(0.0, 0.0, 0.0)
    @velocity = Vector.new(0.0, 0.0, 0.0)
    @name = nil
  end
  @force = Vector.new(0.0, 0.0, 0.0)
end

Instance Attribute Details

#color ⇒ Object

Returns the value of attribute color.



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# File 'lib/spherelab.rb', line 193

def color
  @color
end

#force ⇒ Object

Returns the value of attribute force.



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# File 'lib/spherelab.rb', line 192

def force
  @force
end

#graphic ⇒ Object

Returns the value of attribute graphic.



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# File 'lib/spherelab.rb', line 193

def graphic
  @graphic
end

#mass ⇒ Object

Returns the value of attribute mass.



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# File 'lib/spherelab.rb', line 192

def mass
  @mass
end

#name ⇒ Object

Returns the value of attribute name.



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# File 'lib/spherelab.rb', line 193

def name
  @name
end

#position ⇒ Object

Returns the value of attribute position.



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# File 'lib/spherelab.rb', line 192

def position
  @position
end

#prevx ⇒ Object

Returns the value of attribute prevx.



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# File 'lib/spherelab.rb', line 193

def prevx
  @prevx
end

#prevy ⇒ Object

Returns the value of attribute prevy.



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# File 'lib/spherelab.rb', line 193

def prevy
  @prevy
end

#size ⇒ Object

Returns the value of attribute size.



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# File 'lib/spherelab.rb', line 193

def size
  @size
end

#velocity ⇒ Object

Returns the value of attribute velocity.



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# File 'lib/spherelab.rb', line 192

def velocity
  @velocity
end

Class Method Details

.interaction(b1, b2) ⇒ Object

This class method will compute the interaction between bodies b1 and b2 and update their force vectors. Since the forces on the bodies are the same, but acting in the opposite direction, the force can be calculated just once and then used to update both bodies.



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# File 'lib/spherelab.rb', line 269

def Body.interaction(b1, b2)
  r = b1.position - b2.position
  a = r.norm ** 3
  b1.force.add(r * (b2.mass / a))
  b2.force.add(r * (-b1.mass / a))
end

Instance Method Details

#add_force(b) ⇒ Object

Compute the force exerted on this body by body b and update this body’s force vector.



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# File 'lib/spherelab.rb', line 249

def add_force(b)
  r = @position - b.position
  nr = r.norm ** 3
  mr = b.mass / nr
  @force.add(r * mr)
end

#clear_force ⇒ Object

Reset the force vector to (0,0,0). Called by SphereLab#step_system at the start of each new round of interaction calculations.



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# File 'lib/spherelab.rb', line 241

def clear_force
  @force.x = 0.0
  @force.y = 0.0
  @force.z = 0.0
end

#clone ⇒ Object

Make a copy of this body.



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# File 'lib/spherelab.rb', line 220

def clone
  copy = super
  if graphic
    copy.position = position.clone
    copy.velocity = velocity.clone
    copy.force = force.clone
    copy.graphic = Canvas::Circle.new(prevx, prevy, size, :fill => color)
  end
  return copy
end

#inspect ⇒ Object

Create a string that summarizes the state of this body.



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# File 'lib/spherelab.rb', line 233

def inspect
  name = @name ? @name : ""
  return sprintf "%s: %.3g kg %s %s", name, @mass, @position.inspect, @velocity.inspect
end

#move(dt) ⇒ Object

Update this body’s position by applying the current force vector for dt seconds.



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# File 'lib/spherelab.rb', line 258

def move(dt)
  acc = @force * G * -1.0
  @velocity.add( acc * dt ) 
  @position.add( @velocity * dt )
end