Command-line Ruby application for automating some physics equations based on Newton's Laws. Includes weight, gravity, and acceleration due to gravity.

Newtonian Calculator

class Calculator
  
  attr_accessor :exits
  
  @@constant = 0.0000000000667
  
  def welcome
    puts "\n<< Welcome >>\n\n" 
    puts 'type in "help" to see all available options'
  end
  
  def launch!
    welcome
    input = ""
    until @exits.include?(input)
      print "what would you like to calculate? "
      input = gets.chomp.downcase
      
      case input
      when "help"
        help
      when "h"
        help
      when "gravity"
        calculate_gravity
      when "g"
        calculate_gravity
      when "time"
        calculate_time
      when "t"
        calculate_time
      when "average velocity"
        calculate_a_velocity
      when "a velocity"
        calculate_a_velocity
      when "a v"
        calculate_a_velocity
      when "instantaneous velocity"
        calculate_i_velocity
      when "i velocity"
        calculate_i_velocity
      when "i v"
        calculate_i_velocity
      when "distance"
        calculate_distance
      when "d"
        calculate_distance
      when "acceleration"
        calculate_acceleration
      when "a"
        calculate_acceleration
      when "acceleration due to gravity"
        calculate_acceleration_due_to_gravity
      when "a g"
        calculate_acceleration_due_to_gravity
      when "weight"
        calculate_weight
      when "w"
        calculate_weight
      else
        error(input) unless @exits.include?(input)
      end
    end
    conclude
  end
  
  def help
    puts "\ntype in one of the below"
    puts "  gravity (or 'g')"
    puts "  time (or 't')"
    puts "  average velocity (or 'a velocity', or 'a v')"
    puts "  instantaneous velocity (or 'i velocity', or 'i v'"
    puts "  distance (or 'd')"
    puts "  acceleration (or 'a')"
    puts "  acceleration due to gravity (or 'a g')"
    puts "  weight (or 'w')" + "\n"
    puts "or"
    puts "  nothing"
    puts "  quit (or 'q')"
    puts "  exit (or 'x')"
    puts "to quit\n\n"
  end
  
  def calculate_gravity
    m1                = get_data "mass1", "kg"
    m2                = get_data "mass2", "kg"
    d                 = get_data "distance", "meters"
    # Constant of gravity replaced with calculated value
    result            = (@@constant * m1 * m2) / (d**2)
    puts              get_solution(result, "newtons")
    result_in_pounds  = convert_to_lbs(result)
    puts              get_solution(result_in_pounds, "pounds", false)
  end
  
  def calculate_time
    d       = get_data "distance", "meters"
    a       = get_data "acceleration", "m/s/s"
    result  = Math.sqrt((2 * d) / a)
    puts    get_solution(result, "seconds")
  end
  
  def calculate_a_velocity
    d       = get_data "change in distance", "in meters"
    t       = get_data "time", "seconds"
    result  = d / t
    puts    get_solution(result, "meters/second")
  end
  
  def calculate_i_velocity
    v_initial = get_data "initial velocity", "m/s"
    a         = get_data "acceleration", "m/s/s"
    t         = get_data "time", "seconds"
    result    = v_initial + (a * t)
    puts      get_solution(resultm "meters/second")
  end
  
  def calculate_distance
    v_initial = get_data "initial velocity", "m/s"
    t         = get_data "time", "seconds"
    a         = get_data "acceleration", "m/s/s"
    result    = (v_initial * t) + (0.5 * a * t**2)
    puts      get_solution(result, "meters")
  end
  
  def calculate_acceleration
    v       = get_data "change in velocity", "m/s"
    t       = get_data "time", "seconds"
    result  = v / t
    puts    get_solution(result, "meters/second^2")
  end
  
  def calculate_acceleration_due_to_gravity
    m       = get_data "mass", "kg"
    d       = get_data "distance", "meters"
    result  = (@@constant * m) / (d**2)
    puts    get_solution(result, "meters/second^2")
  end
  
  def calculate_weight
    m                 = get_data "mass", "kg"
    a                 = get_data "acceleration due to gravity", "m/s/s"
    result            = m * a
    puts              get_solution(result, "newtons")
    result_in_pounds  = convert_to_lbs(result)
    puts              get_solution(result_in_pounds, "pounds", false)
  end
  
  def error(invalid_input)
    puts '"' + invalid_input + '" is not a valid action.'
  end
  
  def conclude
    puts "\n<< Goodbye >>"
  end
  
  private
  
  def convert_to_lbs(n)
    n * 0.224808943
  end
  
  def get_data(message, units)
    input  = ""
    until input.to_f != 0.0
      print  "#{message} (in #{units}) = "
      input  = gets.chomp
      if input == "0"
        break
      end
      puts "Please input only digits." unless input.to_f != 0.0
    end
    return input.to_f
  end
  
  def get_solution(result, units, linebreak=true)
    lbreak = "\n" if linebreak == true
    lbreak ||= ""
    "#{lbreak}#{result.to_s.split("e-").join(" * 10^")} #{units}"
  end
  
end

calculator          = Calculator.new
calculator.exits    = %w(nothing quit q exit x)
calculator.launch!