Why do all the planets have different hours in a day?

Question: Why do all the planets have different hours in a day?
- Keywords:
  day,
  hour,
  planet,
  time
Asked by melissamartin123 to Kimberley, Drew on 17 Jun 2011.
- Drew Rae answered on 17 Jun 2011:
  
  Hi Melissa,
  A day is just how long it takes a spot on a planet to go from facing the sun to facing the sun again. There’s no particular reason all planets should spin at the same speed, so they don’t. Venus even spins slowly backwards.

Question: Why do all the planets have different hours in a day?