[FEAT] Add Newton's Law of Gravitation algorithm (#6855)

Co-authored-by: Priyanshu1303d <priyanshu130d@gmail.com>

src/main/java/com/thealgorithms/physics/Gravitation.java

@@ -0,0 +1,66 @@
+package com.thealgorithms.physics;
+
+/**
+ * Implements Newton's Law of Universal Gravitation.
+ * Provides simple static methods to calculate gravitational force and circular orbit velocity.
+ *
+ * @author [Priyanshu Kumar Singh](https://github.com/Priyanshu1303d)
+ * @see <a href="https://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation">Wikipedia</a>
+ */
+public final class Gravitation {
+
+    /** Gravitational constant in m^3 kg^-1 s^-2 */
+    public static final double GRAVITATIONAL_CONSTANT = 6.67430e-11;
+
+    /**
+     * Private constructor to prevent instantiation of this utility class.
+     */
+    private Gravitation() {
+    }
+
+    /**
+     * Calculates the gravitational force vector exerted by one body on another.
+     *
+     * @param m1 Mass of the first body (kg).
+     * @param x1 X-position of the first body (m).
+     * @param y1 Y-position of the first body (m).
+     * @param m2 Mass of the second body (kg).
+     * @param x2 X-position of the second body (m).
+     * @param y2 Y-position of the second body (m).
+     * @return A double array `[fx, fy]` representing the force vector on the second body.
+     */
+    public static double[] calculateGravitationalForce(double m1, double x1, double y1, double m2, double x2, double y2) {
+        double dx = x1 - x2;
+        double dy = y1 - y2;
+        double distanceSq = dx * dx + dy * dy;
+
+        // If bodies are at the same position, force is zero to avoid division by zero.
+        if (distanceSq == 0) {
+            return new double[] {0, 0};
+        }
+
+        double distance = Math.sqrt(distanceSq);
+        double forceMagnitude = GRAVITATIONAL_CONSTANT * m1 * m2 / distanceSq;
+
+        // Calculate the components of the force vector
+        double fx = forceMagnitude * (dx / distance);
+        double fy = forceMagnitude * (dy / distance);
+
+        return new double[] {fx, fy};
+    }
+
+    /**
+     * Calculates the speed required for a stable circular orbit.
+     *
+     * @param centralMass The mass of the central body (kg).
+     * @param radius The radius of the orbit (m).
+     * @return The orbital speed (m/s).
+     * @throws IllegalArgumentException if mass or radius are not positive.
+     */
+    public static double calculateCircularOrbitVelocity(double centralMass, double radius) {
+        if (centralMass <= 0 || radius <= 0) {
+            throw new IllegalArgumentException("Mass and radius must be positive.");
+        }
+        return Math.sqrt(GRAVITATIONAL_CONSTANT * centralMass / radius);
+    }
+}