How often were slaves whipped?

Sadly, Whippings were not uncommon for slaves. Masters saw it as a form of punishment, and thought it would improve their slaves work. Some were whipped more than others but the punishment was more focused on the severity of the beating than the frequency. Slaves were not only whipped but had other punishments, such as being locked in a plantation jail, being mauled by dogs, and being humiliated. From 1840-1841 for a 23 month long period, Bennet H. Barrow kept a diary of how he punished his slaves. Through out this course Barrow had given 160 whippings and 60 of his 77 slaves were whipped at least one time. Barrow also gave reasons for whipping his slaves and eighty percent of the reasoning was for poor work. According to his diary, whippings did not change the behavior of slaves, an yet they endured the pain of whippings. It is unknown whether all slave owners whipped their slaves this often, though Barrow does say that his neighbor was the most cruel man for castrating three of his slaves. Though we do not know exactly how often the majority of slaves were whipped, Barrows diary gives us a look into what it was probably like for most slaves. A troubled, painful life that was not their own.

Question 1:

If whipping did not improve the work of slaves, why do you think slave owners still felt it necessary to whip the slaves?

Question 2: 

Do you think that if slaves did begin to improve their work, that they would be punished less?