feat: add free-fall motion calculations

[nickzerjeski]

Summary

• add free-fall helper methods using constant acceleration formulas
• implement both distance from time and time from distance calculations
• add input validation and tests

Testing

• ruby maths/free_fall_distance_test.rb

Fixes #194

[Copilot]

Pull request overview

Adds a new maths helper for free-fall motion calculations (constant acceleration under gravity), addressing Issue #194 by providing both “distance from time” and “time from distance” APIs with basic domain validation.

Changes:

• Added FreeFallDistance.distance(time:, gravity:) implementing d = 0.5 * g * t^2
• Added FreeFallDistance.time(distance:, gravity:) implementing t = sqrt(2d / g)
• Added Minitest coverage for the core formulas and negative time/distance validation

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
maths/free_fall_distance.rb	Introduces free-fall distance/time helpers, gravity constant default, and domain validation.
maths/free_fall_distance_test.rb	Adds unit tests validating the formulas and negative-input error behavior.

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[Copilot]

STANDARD_GRAVITY is defined inside class << self, so it is not accessible as FreeFallDistance::STANDARD_GRAVITY (it ends up on the singleton class). If you want this constant to be part of the public API (or avoid confusion), define it in the FreeFallDistance class body (outside class << self) and reference it from the class methods.

Suggested change

	class << self
	STANDARD_GRAVITY = 9.80665
	STANDARD_GRAVITY = 9.80665
	class << self

[Copilot]

This file defines a top-level DomainError class, which will be redefined (and can produce warnings/override behavior) if users require multiple maths helpers that also define DomainError (e.g., maths/square_root.rb). Prefer using a built-in exception like ArgumentError, or namespace the error under FreeFallDistance (or define DomainError once in a shared file and require it).

Suggested change

	raise DomainError, 'time must be non-negative' if time.negative?
	raise DomainError, 'gravity must be positive' unless gravity.positive?
	0.5 * gravity * time * time
	end
	# t = sqrt(2d / g)
	def time(distance:, gravity: STANDARD_GRAVITY)
	raise DomainError, 'distance must be non-negative' if distance.negative?
	raise DomainError, 'gravity must be positive' unless gravity.positive?
	Math.sqrt((2.0 * distance) / gravity)
	end
	end
	end
	class DomainError < StandardError; end
	raise ArgumentError, 'time must be non-negative' if time.negative?
	raise ArgumentError, 'gravity must be positive' unless gravity.positive?
	0.5 * gravity * time * time
	end
	# t = sqrt(2d / g)
	def time(distance:, gravity: STANDARD_GRAVITY)
	raise ArgumentError, 'distance must be non-negative' if distance.negative?
	raise ArgumentError, 'gravity must be positive' unless gravity.positive?
	Math.sqrt((2.0 * distance) / gravity)
	end
	end
	end

[Copilot]

Gravity validation (gravity must be positive) is new behavior but is not covered by tests. Add test cases asserting a DomainError is raised for zero/negative gravity in both .distance and .time (or at least one shared validation path if you refactor).