《理论力学 Theoretical Mechanics——静力学》PPT教学课件（双语）：第四章 摩擦 Friction

Theoretical Mechanics Chapter Friction

1 Theoretical Mechanics

理论力学 四擦

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Chapter 4: Friction 84-1 Introduction §4-2 Sliding friction 84-3 Equilibrium problems with friction §4-4 Rolling friction Class of exercises

3 Chapter 4: Friction §4–1 Introduction §4–2 Sliding friction §4–3 Equilibrium problems with friction §4–4 Rolling friction Class of exercises

第四章摩擦 §4-1引言 §4-2滑动摩擦 §4-3考虑摩擦时的平衡问题 §4-4滚动摩擦 习题课

4 第四章 摩擦 §4–1 引言 §4–2 滑动摩擦 §4–3 考虑摩擦时的平衡问题 §4–4 滚动摩擦 习题课

Statics Chapter 4 friction §4-1 Introduction Until now, in solving problems of statics, we regarded the sur faces of contact as absolutely smooth neglecting friction between bodies In fact surfaces without friction do not exist friction exists. in general Example G a a The system is in equilibrium only if friction is taken into account

5 Until now, in solving problems of statics, we regarded the surfaces of contact as absolutely smooth neglecting friction between bodies. In fact surfaces without friction do not exist, friction exists, in general. [Example] Chapter 4 Friction §4-1 Introduction The system is in equilibrium only if friction is taken into account. 

功学 第四章摩擦 §41引言 前几章我们把接触表面都看成是绝对光滑的,忽略了物体 之间的摩擦,事实上完全光滑的表面是不存在的,一般情况下 都存在有摩擦。 「例 G 平衡必计摩擦

6 前几章我们把接触表面都看成是绝对光滑的，忽略了物体 之间的摩擦，事实上完全光滑的表面是不存在的，一般情况下 都存在有摩擦。 [例] 第四章 摩 擦 §4-1 引言 平衡必计摩擦 

Statics 1. why shall we study friction? 2. The way to study friction, to master its laws to use the advantages of friction and to overcome its shortages 3. According to the motion of the surfaces of contact friction can be classified into Sliding Friction (Rolling Friction

7 1. why shall we study friction? 2. The way to study friction, to master its laws, to use the advantages of friction and to overcome its shortages. 3. According to the motion of the surfaces of contact friction can be classified into Sliding Friction Rolling Friction 

功学 为什么研究摩擦? 二、怎样研究摩擦,掌握规律 利用其利,克服其害。 三、按接触面的运动情况看: 摩擦分为∫滑动摩擦 滚动摩擦

8 一、为什么研究摩擦？ 二、怎样研究摩擦，掌握规律 利用其利，克服其害。 三、按接触面的运动情况看： 摩擦分为 滑动摩擦 滚动摩擦 

Statics §4-2 Sliding friction 1. Static force of friction Concept: When two bodies can slide on each other a force of f friction is developed at the sur face of contact which prevents the motion of the bodies. It is called static force of friction. (it is equal to the tangential constraint reaction force with which the surface of contact acts on the bodies 2)Status: static F=P (F growing with P is an unfixed value) @2critical: (It is going to start to slide) Fmax=f N the coefficient of static friction) P③ sliding: FF=fN (the coefficient of kinetic friction The ways to increase the force of friction (increase of the force N. (increase of the coefficient of friction f. CLook for the animation on the next page)

9 1) Concept: When two bodies can slide on each other a force of friction is developed at the surface of contact which prevents the motion of the bodies. It is called static force of friction. (it is equal to the tangential constraint reaction force with which the surface of contact acts on the bodies) §4-2 Sliding Friction 1. Static force of friction (Look for the animation on the next page) The ways to increase the force of friction: ①increase of the force N, ②increase of the coefficient of friction f. 2) Status: ①static: ②critical: (It is going to start to slide) ③sliding: F = P (F growing with P is an unfixed value ) Fmax = f N F = f N ' ' (f — the coefficient of static friction) (f '—the coefficient of kinetic friction)

功学 §4-2滑动摩擦 、静滑动摩擦力 1、定义:相接触物体,产生相对滑动(趋势)时,其接触面 产生阻止物体运动的力叫滑动摩擦力。 (就是接触面对物体作用的切向约束反力) 2、状态:①静止:F=P(P↑-F个不固定值) ②临界:(将滑未滑) G Fm=f·N(f—静滑动摩擦系数) ③滑动:F=f·N(动摩擦系数) 所以增大摩擦力的途径为:①加大正压力N ②加大摩擦系数f (翻页请看动画) 10

10 1、定义：相接触物体，产生相对滑动（趋势）时，其接触面 产生阻止物体运动的力叫滑动摩擦力。 （ 就是接触面对物体作用的切向约束反力） 2、状态： ①静止： ②临界：（将滑未滑） ③滑动： F = P (P  −F  不固定值) Fmax = f N F = f N ' ' §4-2 滑动摩擦 一、静滑动摩擦力 （翻页请看动画） 所以增大摩擦力的途径为：①加大正压力N, ②加大摩擦系数f （f — 静滑动摩擦系数） （f '—动摩擦系数）