Which of the following is an example of increasing friction intentionally?

a. waxing skis
b. adding grease to gears on a bike
c. throwing sand on an icy driveway
d. oiling a squeaky door

When friction is concerned, it represents the surface resistance when moving the body along that surface. The more smooth the surface is, the smaller the friction, the less the surface resistance to the movement of the body.

A. Waxing skis is applied when you want to fill in scratches and cracks in ski boots and thus reduce friction so that riding on the skis is faster.

B. Adding grease to gears on a bicycle and in general gears in mechanical engineering, contributes to reducing friction, better operation without the lag of individual gears.

C. Throwing sand on an ice driveway increases friction because the sand grains have a high friction coefficient, thus reducing the possibility of falling and injuring people, or slipping of car wheels in place.

D. Oiling a squeaky doors reduces friction, which is caused by the corrosion of the door elements, and thus opening and closing the door is easier and without creaking.

The answer is: C.

d. i assume the underlined word is "role." reformat if it isn't.

explanation:

role is closest to part because when replacing words, "playing a vital decision," "playing a vital activity," and "playing a vital dollar" don't make logical sense. the only meaningful choice is "playing a vital part."

this fits one of merriam-webster's definitions of role: "a function or part performed especially in a particular operation or process."

the answer is solomon northrup. he was a free-born african american, abolitionist and professional violinist that was drugged, kidnapped and sold as slave in 1841 and remained in captivity until 1853 where he regained his freedom with the of the then-governor of new york, washington hunt. he wrote and published his memoirs "twelve years a slave" in 1853, and in this text, he tells the story of his escape thru one of louisiana's swamps (the great pacoudrie swamp) in which he ended up covered in green slime from crossing the surface of the dead water.