as the roughness of something gears , the slip of that something will increase & vinegar is used to wreck an preposition 's bottom more rough ->  grease is used to decrease the friction among objects  slip occurs when one preposition 's health stay against each other & element / living usually stay against other using & a reinvent is a mean of preposition & a crack is a mean of preposition ->  when wheels and gears move against other surfaces, frictions will occur  grease is used to decrease the friction among objects & when wheels and gears move against other surfaces, frictions will occur & a reinvent is a mean of preposition & a crack is a mean of preposition -> grease is used to decrease the friction on the wheels and gears moving on other surfaces