Explain the first condition for equilibrium.
Difficulty: Medium
The first condition of equilibrium:
A body is said to satisfy the first condition of equilibrium if the resultant of all the forces acting on it is zero.
Explanation:
Let n number of forces F1, F2, F3,…………., Fn is acting on a body such that
F1+F2+F3+……….+Fn = 0
Or
∑ F= 0……………. (1)
The symbol ∑ is a Greek letter called Sigma used for summation. Equation (1)
Is called the first condition of equilibrium.
The first condition of equilibrium can also be stated in terms of the x and y components.
F_{1x}+F_{2x}+F_{3x}.....+F_{nx} =0
And
F_{1y}+F_{2y}+F_{3y}.....+F_{ny} =0
Or
∑ Fx = 0
And
∑ Fy = 0
Examples:
A book lying on the table or a picture hanging on the wall, is at rest and thus satisfies the first condition of equilibrium and is thus in equilibrium.
A paratrooper coming down with terminal velocity (constant velocity) also satisfies the first condition for equilibrium and is thus in equilibrium.
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