Its all about statics, Lecture notes of Statics

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MOMENT OF A FORCE

Moment of a Force

 The moment of a force about a point or axis measures

the tendency of the force to cause the body to rotate

about the point or axis.

Magnitude of Moment

Where d is the moment arm or perpendicular distance

from the axis at point O to the line of action of the

force.

Problem

1. Determine the moment of the 800 N force acting on

the frame in the figure below about points A, B, C,

and D.

1. Determine the moment of the 800 N

force acting on the frame in the figure

below about points A, B, C, and D.

Moment at pt. A: M୅ =800 N x 2.5 m M୅ = 2000 N − m Moment at pt. B: M୆ =800 N x 1.5 m M୆ = 1200 N − m Moment at pt. C: Mେ =800 N x 0 m Mେ = 0 N − m Moment at pt. D: Mୈ =800 N x^ 0.5 m Mୈ =400 N − m

2. Two forces acting at A and B. It is

required to determine the location of

its resultant from point 0.

ଶ ଶ ଶ ଶ

୭=^ +

RESULTANT OF COPLANAR PARALLEL FORCE SYSTEM

Resultant of Distributed Loads

Problem

 1. Determine the resultant of the parallel force system acting on the bar AB shown below. The forces and positions are given in the figure.

Problem

 2. Determine the resultant force and specify where it acts on the beam measured from A.

2. Determine the resultant

force and specify where it

acts on the beam measured

from A.

R = ΣFy + 900 lb + 150 lb (^) + 500 lb 𝐑 = 155 𝟎 𝐥𝐛 Rd = ΣFx (1550 lb)d = (^) (900 lb x 3 ft) + (150 lb x 4 ft) 𝐝 = 5.03 𝐟𝐭

୅=^

1 2 ( 50 lb ft ) 6 ft = 150 lb 150 lb ft 6ft = 900 lb R = 3 ft 2 3 6ft = 4 ft

• (500 lb x 9 ft)