characteristics [,k æ rəktə'ristiks] n. 特性，特征；特色（ characteristic 的复数）；特质
Friction: Layout coulomb ['ku:lɒm] n. 库仑 wedge [wedʒ] n. 楔子；楔形物；
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Types of Friction
Characteristics of Dry Friction
Coulomb ’ s Friction Model
Friction Angle
Simple Application: Wedge

lubricate ['lubrikeit] vi. 润滑； adjacent [ə'dʒeisənt] adj. 邻近的，毗连的 cyclical ['saiklikəl] adj. 周期的，循环的
Types of Friction
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Dry Friction
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When the unlubricated surfaces of two solids are in contact under a condition of sliding or tendency to slide
• Fluid Friction
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When adjacent layers in a fluid are moving at different velocities
• Internal Friction
- When solid materials are subjected to cyclical loading

Characteristics of Dry Friction
F t
: Friction Force
N: Normal Force

critical ['krɪtɪk(ə)l] adj. 临界的； impend 英 [ɪm'pend] vi. 即将发生 kinetic [kɪ'netɪk] adj. [ 力 ] 运动的；动力的 coefficient [,kəui'fiʃənt] n. [ 数 ] 系数

incline [in'klain] vi. 倾斜； value ['v æ lju:] n. 值；
Friction: Example I
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A block of mass m is resting on an inclined plane. The coefficient of friction between the block and the plane is µ
=0.25. Determine the maximum value of the inclining angle θ.
Note: Inclining the plane may be used to estimate the coefficient of friction

Friction Force
- Direction
- Magnitude
Coordinate System
- Standard
- Rotated

Friction: Example II
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Determine the range of values of force P applied so that the block of mass m will neither slide down or move up the inclined plane. Assume that the coefficient of friction between the block and the plane is µ =0.25 and the inclining angle of the plane is θ=45 º .

Friction: Example II
Friction Force: Direction ?

Friction: Example II

square [skwεə] adj. 平方的；正方形的； subject ['sʌbdʒikt] adj. 受制于 … 的 tilt [tilt] vi. 倾斜；
Friction: Example III
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A square block of mass m resting on the horizontal surface is subjected to a horizontal force P. The coefficient of friction between the block and the plane is µ . Prove that equilibrium is broken by sliding if µ <0.5, and by the block tilting if µ >0.5.

Friction: Example IV
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The three flat blocks are positioned on the 30 º incline and a force P parallel to the incline is applied to the middle block. The coefficient of friction for each of the three pairs of mating surfaces is shown. Determine the maximum value of P may have before any slipping takes place.

Friction: Example IV

The Angle of Friction

respectively [ri'spektivli] adv. 分别地；各自地，独自地
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Wedge: Example V
The position of the 500kg block is adjusted by the 5 º wedge under the action of the force P. If the coefficients of friction for both pairs of wedge surfaces and between the block and the horizontal plane are 0.3 and 0.6 respectively, determine the least force P required to move the block.