勢い:いきおい: momentum, the power to influence something - like "The car had a lot of 勢い so it was hard to stop the car before we hit the cat" or "Because of the whiskey's 勢い, I could do a table dance in the White House." Also means to gain steam or lose steam - said of political momentum or the momentum of a trend or idiology.

力;ちから: force or strength (of a person but also of a thing - tidal wave, lightnight, mighty rhino, etc.)

権力:けんりょく: power (over other people)(as in boss, parent, governor, pope, etc.)