Yes I had to do a report on this in my history class in 1968. Its true. The story was that Truman wanted to see what the bomb would do and he also wanted to show Russia what it would do. Shame
Nonsense. We already knew what the bombs could do from the Trinity test. And there was no need to bomb Japan in order to scare Russia; they could just be invited to witness some peacetime A-bomb tests if necessary.
The first A-bomb was dropped on Japan because: Japan was refusing to surrender.
The second A-bomb was dropped on Japan because: Japan was still refusing to surrender.
The third A-bomb was not dropped on Japan because: Japan had surrendered.