当载荷超过某一定范围时,在去除载荷后,变形只能部分恢复而残留下一部分变形不能消失,材料的这种性质称为()
A.弹性
B.弹性变形
C.塑性
D.塑性变形
参考答案:C
运动员用双手握住竖直的滑杆匀速上攀和匀速下滑时,运动员所受到的摩擦力分别是f1和f2,那么 [ ]
A.f1向下,f2向上,且f1=f2
B.f1向下,f2向上,且f1>f2
C.f1向上,f2向上,且f1=f2
D.f1向上,f2向下,且f1=f2
A person referring to the stern sheets of a lifeboat is speaking of().
A.the line attached to the tack of the lugsail
B.the emergency rudder
C.a canvas awning
D.the aftermost seating