Statics Force system: a group of forces acting on a body Balanced force system: if a body subjected to a A force system is in equilibrium state, /F we call the system to be a balanced 2. Rigid body a body which does not change its shape and dimension under applied forces is called a rigid body 3. Equilibrium state a body is called to be in the state of equilibrium if it does not move or if it moves with an uniform velocity
11 Force system: a group of forces acting on a body. Balanced force system: if a body subjected to a force system is in equilibrium state, we call the system to be a balanced. A body is called to be in the state of equilibrium if it does not move or if it moves with an uniform velocity. 2.Rigid body A body which does not change its shape and dimension under applied forces is called a rigid body 3.Equilibrium state A F
学 力系:是指作用在物体上的一群力 平衡力系:物体在力系作用下处于平衡, 我们称这个力系为平衡力系 刚体 就是在力的作用下,大小和形状都不变的物体。 三.平衡 是指物体相对于惯性参考系保持静止或作匀速直线运 动的状态
12 力系：是指作用在物体上的一群力。 平衡力系：物体在力系作用下处于平衡， 我们称这个力系为平衡力系。 是指物体相对于惯性参考系保持静止或作匀速直线运 动的状态。 二.刚体 就是在力的作用下，大小和形状都不变的物体。 三.平衡 A F
Statics 81-2 Principles of statics Principles: conclusions obtained from longtime practice and from many experiments. They are repeatedly proved by practice and now are recognized without prove Ist Principle: two force equilibrium a rigid body subjected to the action of two forces can be in equilibrium the necessary and sufficient conditions are fi the two forces are equal in magnitude,|F1l=|F2l the two forces are opposite in direction, F1=-F2 刚体) the two forces are collinear, the two forces act on the same body 13
13 §1-2 Principles of statics Principles: conclusions obtained from longtime practice and from many experiments. They are repeatedly proved by practice and now are recognized without prove. 1st Principle: two force equilibrium A rigid body subjected to the action of two forces can be in equilibrium, the necessary and sufficient conditions are: the two forces are equal in magnitude, | F1 | = | F2 | the two forces are opposite in direction, F1 = –F2 the two forces are collinear, the two forces act on the same body
学 §1-2静力学基本公理 公理:是人类经过长期实践和经验而得到的结论,它被反复的 实践所验证,是无须证明而为人们所公认的结论。 公理1二力平衡公理 作用于刚体上的两个力,使刚体平衡的必要与充分条件是: 这两个力大小相等|F1=|F2 所方向相反F1=-2 刚体 作用线共线, 作用于同一个物体上
14 §1-2 静力学基本公理 公理：是人类经过长期实践和经验而得到的结论，它被反复的 实践所验证，是无须证明而为人们所公认的结论。 公理1 二力平衡公理 作用于刚体上的两个力，使刚体平衡的必要与充分条件是： 这两个力大小相等 | F1 | = | F2 | 方向相反 F1 = –F2 作用线共线， 作用于同一个物体上
Statics Explanation: CAs far as rigid bodies are concerned, the conditions above are necessary and sufficient 2As far as deformable bodies are concerned, the conditions above are only necessary F F (deformable body) string bodies double force equivalent body: is a rigid body subjected to two forces must be in equilibrium F2 Double force Fi F equivalent rod Double force equivalent body 15
15 Explanation: ①As far as rigid bodies are concerned, the conditions above are necessary and sufficient. ②As far as deformable bodies are concerned, the conditions above are only necessary. bodies (deformable body) string 二力杆 Double force equivalent body Double force equivalent rod ③double force equivalent body: is a rigid body subjected to two forces must be in equilibrium