ES 1 Reviewer - Terms

Mechanics

the science that which describes and predicts the conditions of rest or motion of bodies under the act of forces.
it is an implied science

Length

A physical quantity of a geometric measurement between two points.
It is needed to locate the position of a point in space.

Space

Associated with the notion of the position of a point, P, given in terms of three coordinates measured from a reference point or origin.

Time

Definition of an event requires specification of the time and position at which it occurred

Mass

Amount of matter an object contains.
Used to characterize and compare bodies.

Force

Represents the action of one body on another.
Characterized by its point of application magnitude and direction.

Strength of Materials

the study of the internal effect of external forces applied to structural members. Stress, strain deformation, deflection, flexure, shear diagram and moment diagrams are some of the topics covered.

Pa

Conversion for N/m²

MPa

Conversion for N/mm²

PSI

Conversion for lb/in²

External force

Force generated outside a body

Internal Force

Force generated inside a body.

Applied force

External force on the body that tries to change the state of movement of the body.

Reaction force

external force that inhibits change in the state of movement of a body when acted on by an applied force.

Distributed force

A force density

Concurrent

forces whose lines of action pass through a common point.

Parallel

forces whose lines of actions are parallel

Non-concurrent

forces whose lines of actions are neither parallel nor intersect in a common point

Newton’s first law

if the resultant force on a particle is zero, the particle will remain at rest or continue to move in a straight line.

Newton’s second law

A particle will have an acceleration proportional to a non-zero resultant force.

Newton’s third law

The forces of action and reaction between two particles have the same magnitude and line of action with opposite sense.

Principle of Transmissibility

The external effect of a force on a body is the same for all points of application along its line of action.

Fixed or Bound Vectors

Have well defined points of application that cannot be changed without affecting an analysis

Free vectors

may be freely moved in space without changing their effect on an analysis

Sliding Vectors

May be applied anywhere along their line of action without affecting an analysis.

Equal vectors

have the same magnitude and direction

Negative vector

has the same magnitude and the opposite direction of a given vector

Components of a force in terms of x axis

Components of a force in terms of y axis

First Quadrant

X - positive
Y - positive

Second Quadrant

X - negative
Y - positive

Third Quadrant

X - negative
Y - negative

Fourth Quadrant

X - negative
Y - negative

Moments of a Force

Is the measure of the tendency of a force F to make the rigid body rotate about a fixed axis perpendicular to the plane of the force F.

Statics

Deals primarily with the calculation of external forces which act on rigid bodies in equilibrium

Rigid body

is a combination of a large number of particles occupying fixed positions with respect to each other.

1

Number of unknowns in a Slider or Constrained pin

3

Number of unknowns in a Fixed support

1

Number of unknowns in:
Cables
Rollers
Sliders
Rocker
Member pinned to Collar
Weightless links

2

Number of unknowns in:
Pin or Hinge
Member Fixed to collar

Truss

a structure composed of slender members joined together at their endpoints.

Wooden struts and Metal bars

Common construction materials for Trusses

Planar Trusses

lie in a single plane and are often used to support roofs and bridges

Truss members

connected at their extremities only; thus no member is continuous through a joint.

Tension

Member reaction due to pulling forces at both ends and is denoted by (T); lengthening force

Compression

Member reaction due to pushing forces at both ends denoted by (C); shortening force

Method of Sections

Consist of cutting a truss into two sections at a point where the bar force is required.