Wedge Friction

Wedge Friction

• Wedges are used to either raise large loads or to keep large loads in place by inserting a wedge below the loads.

• Problems involving wedges can be solved by drawing F.B.D. of ach object and using conditions of equilibrium.

• The direction of impending motion is important in such problems which decides the direction of frictional force...

Note:

• To raise the block A shown in Fig. 8.10.1, the direction of impending motion for A will be upward and for B it will be towards right.

• To support the block A, the impending motion will be downward for A and towards left for B.

Solved Examples for Understanding

Example 8.10.1 

A block 'A' weighing 80 kN is to be moved towards left by light wedge B. Find necessary force 'P', if angle of friction at all rubbing surfaces is 15°. Refer Fig. 8.10.2

Solution:

Example 8.10.2 

Determine the minimum force 'P' required to overcome static friction and begin to lift 100 N block 'A' shown in Fig. 8.10.3. The weight of 20° wedge 'B' is 5 N and the coefficient of static friction between all surfaces is 0.4.

Solution: 

The two free body diagrams are shown in Fig. 8.10.3 (a).

Example 8.10.3 

A block of 1000 N is to be raised up by means of force P each acting on wedges as shown in Fig. 8.10.4. If angle of friction at all rubbing surfaces is 15°, determine P. Ignore weight of wedge.

Solution :

Example 8.10.4 

Find the minimum horizontal force 'P' to be applied to block 'A' weighing 500 N so as to keep block 'B' of 1500 N in limiting condition of equilibrium. Refer Fig. 8.10.5.

Solution: 

For minimum force P, block B has tendency to move downward and A has tendency to move towards left. The F.B.D. of blocks A and B are shown in Fig. 8.10.5 (a).

Example 8.10.5 

Block A supports a pipe column and rests, as shown in Fig. 8.10.6, on wedge B. μs = 0.25 at all surfaces of contact. Determine: 

a) The angle 0 for which sliding is impending, and 

b) The corresponding force exerted on the block by the vertical wall.

Solution: 

The impending motion of A is downwards while that of B is towards right. The free body diagrams are shown in Fig. 8.10.6 (a).