Text: low self-confidence is a potential cause for failure in both private life with family and friends and in professional life at work.

Correct capitalization: Low self-confidence is a potential cause for failure in both private life with family and friends and in professional life at work.

Text: the old instruments were made of hammered pieces of metal, which gives a more or less rough surface. that makes it easier to play "off-side" the natural tones.

Correct capitalization: The old instruments were made of hammered pieces of metal, which gives a more or less rough surface. That makes it easier to play "off-side" the natural tones.

Text: when cuba was conquered velazquez became the governor of cuba and cortez became a clerk to the treasurer.

Correct capitalization: When Cuba was conquered Velazquez became the governor of Cuba and Cortez became a clerk to the treasurer.

Text: the rotational speed of the blade up to 6800 rpm. / min

Correct capitalization:
The rotational speed of the blade up to 6800 rpm. / min