Capital letter should be used for proper names-- formal-official names of things and people.
At the beginning, the start of a quote, or in a proper noun.
She stopped talking mid-sentence when she realized she had forgotten an important detail.
Yes, the word "world" should not be capitalized in the middle of a sentence unless it is a proper noun or part of a title.
I am so ready for the mid-semester break!
Yes, the word "police" should be capitalized because it is a proper noun when referring to a specific police department or organization (e.g., New York Police Department).
She arrived at the cafe in the mid-afternoon, just as the sun was starting to dip below the horizon.
no
She stopped talking mid-sentence when she realized she had forgotten an important detail.
We hold our mid-week conference on Wednesday afternoons at two. When I walked into the room, Mary stopped what she was saying in mid-sentence.
It should only be capitalized if it's used to substitute a name.
mid Atlantic ridges
ships and buildings
toulouse toulouse toulouse
toulouse toulouse toulouse
The Mid-Ocean Ridge Is From The Mantle.
Yes, the word "police" should be capitalized because it is a proper noun when referring to a specific police department or organization (e.g., New York Police Department).
Canberra is the capital city of Australia. Its population in mid 2013 was about 379 000.
A question, properly written, cannot be asked mid sentence. It is a sentence on its own. Though it could be asked mid paragraph, For instance; "How could I compare thee to a summers day?" Could be asked mid paragraph.