Question: in the universal law of gravitation what does the symbol r stand for
[{'answer': 'distance', 'provenance': [{'wikipedia_id': '38454', 'title': 'Gravitational constant', 'start_paragraph_id': 2, 'start_character': 171, 'end_paragraph_id': 2, 'end_character': 179, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '38454', 'title': 'Gravitational constant', 'start_paragraph_id': 7, 'start_character': 0, 'end_paragraph_id': 7, 'end_character': 264, 'bleu_score': 0.7395891035716361, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 15809136404849957488}, 'section': 'Section::::Definition.\n'}]}]