First condition of equilibrium
Force – push or pull
Types:
1. Weight (W) – force acting at the center of gravity of a body or system which is
directed vertically downward.
2. Normal force (N) – force that is acting almost always upward perpendicular to
surface contact.
3. Tension (T) – force acting along the line but away from the point of
consideration.
4. Compression (C) – force acting along the line towards the point of consideration.
5. Friction (f) – force that tends to resist the impending motion or the motion of a
body.
Classification of force
1. Concurrent force – acting at a common point within a body.
2. Nonconcurrent force – force acting at different points within a body.
Newton’s first law of motion – in the absence of an unbalanced force a body at rest will
remain at rest and a body moving with constant velocity along a straight path will
continue to move in such motion.
First condition of equilibrium
For a body to remain at rest the resultant or unbalanced force must be equal to zero.
Therefore,
Σx = 0
Σy = 0
R=0
Procedure;
1. Sketch the problem showing all necessary data.
2. Draw the equivalent “free body diagram”
- isolated sketch of the problem showing only the forces acting on
the system.
Sample problems
1. Solve for the tension on the cord and the compression on the wooden bar. (neglect
the weight of the wooden bar)
60O
45O
600N
2. A cylinder weighing 400 N is held against a smooth inclined plane by means of
weightless rod AB as shown in the figure. Determine the force P and N exerted
on the cylinder b the rod an inclined plane respectively.
B
W
A
25O
55O
3. Determine the tension on the cords.
80O
40O
50O
60O
200N
400N