The second sentence is correct because there is an adverb /slowly/ modifying the verb. 'Slow' is an adjective which modifies nouns. So the first sentence is not correct. According to Etymology Online Dictionary, since the 15th century 'slow' has been both an adjective and adverb. These homonyms are marked in all English Dictionaries. But 'slowly' is used as well. So in many cases there is no difference between 'slow' and 'slowly', for example: to work/drive slow/slowly. To my mind, according to a current tendency, 'slow' seems more informal than 'slowly'.

The second sentence is grammatically more correct because there is an adverb /slowly/ modifying the verb. 'Slow' is an adjective which modifies nouns. So the first sentence is not grammatically correct. But according to Etymology Online Dictionary, since the 15th century 'slow' has been both an adjective and adverb. These homonyms are marked in all English Dictionaries. But 'slowly' is used as well. So in many cases there is no difference between 'slow' and 'slowly', for example: to work/drive slow/slowly. To my mind, according to a current tendency, 'slow' seems more informal than 'slowly'.

The second sentence is correct because there is an adverb /slowly/ modifying the verb. 'Slow' is an adjective which modifies nouns. So the first sentence is not correct.

The second sentence is correct because there is an adverb /slowly/ modifying the verb. 'Slow' is an adjective which modifies nouns. So the first sentence is not correct. According to Etymology Online Dictionary, since the 15th century 'slow' has been both an adjective and adverb. These homonyms are marked in all English Dictionaries. But 'slowly' is used as well. So in many cases there is no difference between 'slow' and 'slowly', for example: to work/drive slow/slowly. To my mind, according to a current tendency, 'slow' seems more informal than 'slowly'.