UNIVERSITY OF RIZAL SYSTEM
MORONG CAMPUS
COLLEGE OF ENGINEERING
CIVIL ENGINEERING PROGRAM
Statics of Rigid Bodies
ES 2
Activity #1
Picones, Ian B.
2 CE B
August 5, 2025
Engr. Jasmin M. Panganiban
Instructor
1. Discuss two examples where the concept of statics is applied in real life situation.
1.1. Bridge Construction
The components of a bridge, such as beams, trusses, and pillars, are considered rigid
bodies because they maintain their shape under load and do not deform significantly during
use. The bridge experiences external forces like the weight of vehicles, pedestrians, wind
loads, and its own weight (gravity). These forces act on the bridge structure and cause stress.
Internal forces develop inside the bridge components such as tension, compression, shear,
and bending moments. These internal forces resist the external loads to prevent failure or
collapse.
1.2. A Person Sitting on a Chair
The chair (legs, seat, backrest) and the person’s body are treated as rigid bodies. The
person exerts a downward force (weight due to gravity) on the chair. The chair exerts an
upward normal force on the person. These forces are external to each body but interact at
the contact points. Within the chair, internal forces develop to resist bending and
compressive stresses, especially in the legs and joints due to the person’s weight. Same as
the muscles and bones in the person’s body experience internal forces to maintain posture.
2. Differentiate statics, dynamics and mechanics of deformable bodies using
examples.
Statics deals with rigid bodies that are at rest or moving with constant velocity,
focusing on the balance of forces to maintain equilibrium for example, a person sitting on a
chair where the downward weight is balanced by the upward support force of the chair. In
this case, internal forces develop within the chair legs and joints to resist bending and
compression caused by the person’s weight. Dynamics studies bodies in motion caused by
unbalanced forces, such as a car accelerating across a bridge, where forces like engine
thrust and friction result in changes in velocity. Here, motion and acceleration are analyzed
using Newton’s laws to understand how forces affect the moving object. Mechanics of
deformable bodies, however, examines how materials change shape and size under load,
like bridge beams bending slightly under the weight of heavy vehicles. Unlike rigid bodies,
deformable bodies experience internal stresses and strains, which must be carefully
calculated to prevent failure. While statics assumes no deformation and focuses on
equilibrium of forces, dynamics includes motion and acceleration but still often treats
bodies as rigid.
