Problem 506 | Friction

Problem 506
A 400 lb block is resting on a rough horizontal surface for which the coefficient of friction is 0.40. Determine the force P required to cause motion to impend if applied to the block (a) horizontally or (b) downward at 30° with the horizontal. (c) What minimum force is required to start motion?


Friction is the contact resistance exerted by one body when the second body moves or tends to move past the first body. Friction is a retarding force that always acts opposite to the motion or to the tendency to move.

Problem 002-mm | Method of Members

Problem 002-mm
Members AB and BC shown in Fig. F-002(MM) are pinned together at point B, and are pinned to the floor at points A and C. The structure supports a pulley at point B with which, a person is hoisting a 2.0 kN load. Member BC has a weight of 1.6 kN, which may be considered to act at its center, while AB is made of strong-light material and has negligible weight. Determine the value of the external support reactions at A and C.



Method of Members | Frames Containing Three-Force Members

A three-force member is in general a non-axial member that is not simply in tension or compression. A member of this kind has shear forces perpendicular to the member and subjected to bending loads. If forces are applied to more than two positions on the member, it is three-force member. Any beam is a three-force member according to the above definition.

Frames are pin-connected structures with some or all members are three-force members. To analyze a frame, we can disconnect the three-force member from the structure and draw the free-body diagram of the member. This approach is called the method of members.