Diploma Engineering mechanics-unit 3.pptx

Mech

1. 1 Module-2: Equlibrium of Bodies Learning outcomes: Equilibrium and It’s principles Types of Equilibrium Freebody daigram and it’s procedure Conditions of Equilibrium Lami’s theorm

2. 2 Equilibrium and It’s principles If the resultant of number of forces acting on a body is zero then the body will be in equilibrium. Such a set of forces, whose resultant is zero are called equilibrium forces. The force, which brings the set of forces in equilibrium is called an equilibrant. As a matter of fact, the equilibrant is equal to the resultant force in magnitude, but opposite in direction.

3. 3 Equilibrium and It’s principles PRINCIPLES OF EQUILIBRIUM Though there are many principles of equilibrium, yet the following three are important from the subject point of view : Two force principle. As per this principle, if a body in equilibrium is acted upon by two forces, then they must be equal, opposite and collinear. Three force principle. As per this principle, if a body in equilibrium is acted upon by three forces, then the resultant of any two forces must be equal, opposite and collinear with the third force (The three forces must be concurrent). Four force principle. As per this principle, if a body in equilibrium is acted upon by four forces, then the resultant of any two forces must be equal, opposite and collinear with the resultant of the other two forces.

4. 4 1. Stable equilibrium: A body is said to be in stable equilibrium, if it returns back to its original position, after it is slightly displaced from its position of rest. 2. Unstable equilibrium A body is said to be in an unstable equilibrium, if it does not return back to its original position, and heels farther away, after slightly displaced from its position of rest 3. Neutral equilibrium A body is said to be in a neutral equilibrium, if it occupies a new position (and remains at rest in this position) after slightly displaced from its position of rest. Types of Equilibrium

5. 5 Freebody daigram and it’s procedure A free-body diagram is a representation of an object with all the forces that act on it.  The external environment (other objects, the floor on which the object sits, etc.), as well as the forces that the object exerts on other objects, are omitted in a free-body diagram. Procedure: Draw an outlined shape. Imagine the body to be isolated or cut “free” from its constraints and draw its outlined shape. Show all the external forces and couple moments. These typically include: a) applied loads, b) the weight of the body, and c) support reactions (can be difficult). Label loads and dimensions: All known forces and couple moments should be labeled with their magnitudes and directions.

6. 6 Freebody daigram and it’s procedure Supports and Reactions:

7. 7 Freebody daigram and it’s procedure Examples:

8. 8 Conditions of Equilibrium E When a body is in equilibrium, the resultant of all forces acting on it is zero.Thus, the resultant force R and the resultant moment M are both zero.

9. 9 Lami’s theorm It states, “ If three coplanar forces acting at a point be in equilibrium, then each force is proportional to the sine of the angle between the other two.” Mathematically, P/sin α = Q/sin β = R/sin γ BC = P and AC = Q ∠ AOC = (180° – β ) and ∠ ACO = ∠ BOC = (180° – α) ∠ CAO = 180° – (∠ AOC + ∠ ACO) = 180° – [(180° – β) + (180° – α)] = 180° – 180° + β – 180° + α = α + β – 180° But α + β + γ = 360° Subtracting 180° from both sides of the above equation, (α + β – 180°) + γ = 360° – 180° = 180° or ∠ CAO = 180° – γ

10. 10 Lami’s theorm

11. 11