From a7bc930133c6cb7908cbc310d9b391bde39c78b3 Mon Sep 17 00:00:00 2001
From: nickzerjeski <nick@zerjeski.de>
Date: Mon, 13 Apr 2026 10:51:59 +0200
Subject: [PATCH 1/2] feat: add free fall distance and time helpers

Fixes: #194
---
 maths/free_fall_distance.rb      | 26 ++++++++++++++++++++++++++
 maths/free_fall_distance_test.rb | 26 ++++++++++++++++++++++++++
 2 files changed, 52 insertions(+)
 create mode 100644 maths/free_fall_distance.rb
 create mode 100644 maths/free_fall_distance_test.rb

diff --git a/maths/free_fall_distance.rb b/maths/free_fall_distance.rb
new file mode 100644
index 0000000..bae680b
--- /dev/null
+++ b/maths/free_fall_distance.rb
@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+# Free-fall helpers based on constant acceleration motion.
+class FreeFallDistance
+  class << self
+    STANDARD_GRAVITY = 9.80665
+
+    # d = 0.5 * g * t^2
+    def distance(time:, gravity: STANDARD_GRAVITY)
+      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
diff --git a/maths/free_fall_distance_test.rb b/maths/free_fall_distance_test.rb
new file mode 100644
index 0000000..ae25015
--- /dev/null
+++ b/maths/free_fall_distance_test.rb
@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+require 'minitest/autorun'
+require_relative './free_fall_distance'
+
+class FreeFallDistanceTest < Minitest::Test
+  def test_distance_from_time
+    assert_in_delta 19.6133, FreeFallDistance.distance(time: 2.0), 1E-4
+  end
+
+  def test_time_from_distance
+    assert_in_delta 2.0, FreeFallDistance.time(distance: 19.6133), 1E-4
+  end
+
+  def test_negative_time_raises
+    assert_raises DomainError do
+      FreeFallDistance.distance(time: -1.0)
+    end
+  end
+
+  def test_negative_distance_raises
+    assert_raises DomainError do
+      FreeFallDistance.time(distance: -1.0)
+    end
+  end
+end

From 4138f9fdb4bbf4bff8db8fd379c69ac8b0d61d91 Mon Sep 17 00:00:00 2001
From: Nick Zerjeski <57059725+nickzerjeski@users.noreply.github.com>
Date: Tue, 14 Apr 2026 09:59:10 +0200
Subject: [PATCH 2/2] Apply suggestions from code review

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
---
 maths/free_fall_distance.rb | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/maths/free_fall_distance.rb b/maths/free_fall_distance.rb
index bae680b..2aee86a 100644
--- a/maths/free_fall_distance.rb
+++ b/maths/free_fall_distance.rb
@@ -2,25 +2,23 @@
 
 # Free-fall helpers based on constant acceleration motion.
 class FreeFallDistance
-  class << self
-    STANDARD_GRAVITY = 9.80665
+  STANDARD_GRAVITY = 9.80665
 
+  class << self
     # d = 0.5 * g * t^2
     def distance(time:, gravity: STANDARD_GRAVITY)
-      raise DomainError, 'time must be non-negative' if time.negative?
-      raise DomainError, 'gravity must be positive' unless gravity.positive?
+      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 DomainError, 'distance must be non-negative' if distance.negative?
-      raise DomainError, 'gravity must be positive' unless gravity.positive?
+      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
-
-class DomainError < StandardError; end