time exposure with flash!

[Fotografer]

I am using a Nikon D40,</p>
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<p>I'm trying to get the effect that is seen often in Nightclub photography, where the subject is photographed with flash after the shutter has been open for a second. The end result being a solid subject with light trails and motion blur.</p>
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<p>Is this something to do with 'Rear curtain sync?'</p>
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<p>What do I need to do? </p>
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<p>How do I control the shutter speed before the flash?</p>
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