63) When a load W is suddenly applied to a bar of weight W₁, the stress induced in the bar will increase with the increase in weight W₁.

64) The endurance limit for a mirror polished material will be __________ as compared to unpolished material.

65) A sliding bearing which operates without any lubricant present, is called

66) The material used for brake lining should have __________ coefficient of friction.

67) Screws jacks have multiple threads.