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simulation/gravity.py

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+
+def get_gravity_force(a, b, g):
+    """Gravity is a force of attraction between objects. 
+    The attraction between two objects is equal to their masses
+    multipled together, divided by the square of the distance between them, 
+    times a constant g. This is the real-life definition of gravity. 
+    """
+    a_to_b = b.position - a.position
+    distance = a_to_b.mag()
+    force = a_to_b.scale(g * a.mass * b.mass / (distance * distance))
+    return force
+    a.acceleration += force
+    b.acceleration -= force