如图所示，物体静止于水平桌面上，则（） A．桌面对物体的_爱下问搜题

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问题选择题

如图所示，物体静止于水平桌面上，则（　　）

A．桌面对物体的支持力的大小等于物体的重力，这两个力是一对平衡力

B．物体所受的重力和桌面对它的支持力是一对作用力与反作用力

C．物体对桌面的压力就是物体的重力，这两个力是同一种力

D．物体对桌面的压力和桌面对物体的支持力是一对平衡的力

答案

A、物体的重力是作用在物体上的力，支持力也是作用在这个物体上的力，这两个力大小相等、方向相反且作用在同一直线上，所以这两个力是一对平衡力，故A正确；

B、物体所受的重力和桌面对它的支持力是一对平衡力，作用在同一个物体上，不是一对作用力与反作用力，故B错误；

C、压力不是重力，它们的施力物体、受力物体、作用点都不相同，故C错误；

D、桌面受到的压力与桌面提供的支持力为作用力与反作用力，故不是平衡力，故D错误；

故选A．

选择题

下列各式中，积最小的是（　　）

C．0.005×2040

填空题

Motivation is "the driving force within individuals that impels them to action." And goals are the sought-after results (1) motivated behavior.
Motivation can be either positive or negative (2) direction. We may feel a driving force toward some object or condition, (3) a driving force away from some object or condition. For example, a person may be impelled toward a restaurant to fulfill a need, hunger, and away (4) an airplane to fulfill a need of safety. Some psychologists refer to positive drives (5) needs, wants or desires, (6) negative drives as fears or aversions. (7) , though negative and positive motivational forces seem to differ dramatically (8) terms of physical and sometimes emotional activity, they are basically similar in (9) they both serve to initiate and sustain human behavior. (10) this reason, researchers often refer (11) both kinds of drives or motives as needs, wants and desires.
Goals, (12) , can be either positive or negative. A positive goal is one toward (13) behavior is directed and it is often referred to as an approach object. A negative goal is (14) from which behavior is directed away and it is sometimes referred to as an avoidance object. Since both approach and avoidance goals can be considered objectives of motivated behavior, most researchers refer to (15) types simply as goals. Consider this example. A middle-aged woman may wish to remain (16) attractive as possible. Her positive goal is to appear desirable, and (17) she may use a perfume advertised to make her irresistible. A negative goal may be to prevent her skin (18) aging, and therefore she may buy and use face creams. (19) the former case, she uses perfume to help her achieve her positive goal -- attractiveness; in the (20) case, she uses face creams to help avoid a negative goal -- wrinkled skin.