Statics Quiz 1 | Quizlet

Force Classification

• Concentrated (load)

• Distributed load

• External

• Internal

Particle

◦ mathematical model of an object as a mass point

◦ has mass but no size

◦ A) W = mg for unrestrained/near earth

‣ W = weight of the body

‣ m = Mass, g = acceleration due to gravity

◦ g=9.81 m/s^2

Mass

◦ Scalar quantity

◦ Amount of material in body

◦ Measure of inertia (measure of the resistance to a change in motion

◦ same in any gravitational field

◦ Units: Slugs and kilograms; 1 slug = 14.59 kilograms

Weight

◦ Vector

◦ Effect of gravity on body

◦ Measure of force exerted on a body by gravitational field

◦ Varies with the strength of gravitational pull

◦ pounds and newtons; 1 lb = 4.448 N

Rigid Body

A mathematical model of a material body or system of particles in which the distance between any two particles remains constant

scalar or vector

• Scalar; quantity which can be completely specified WITHOUT mentioning a direction

• Vector; A quantity completely specified by mentioning magnitude and direction and which add according to the parallelogram law

◦ Displacement, velocity, acceleration, momentum, or force

Types of Vectors

Free Sliding Bound Force

Free

has a definite mag. and direction but no specific location in space

Sliding

One which can be moved along a given line collinear with the vector itself

Bound

one with specified point of application

Force

Defined as that quantity which tends to change the state of motion of a body (push or pull)

Concentrated

effect of loading which is assumed to act at a point on a body

Distributed load

A force or force system spread over an area, either uniformly or non uniformly

External

acting on or outside of a structure set in equilibrium

Internal

force effect within the entity or any component part of a structure set in equilibrium

Force Systems

(when several forces act in a given situation ) can be classified according to the arrangement of the lines of action of the forces in the system

Collinear forces

Acting along same line of action

Coplanar forces

Forces that all lie in the same plane

Concurrent forces

Forces that all intersect at a common point

General Space Force System

Non-coplanar, non-parallel, non-concurrent, con-collinear force system (look at picture on page 7)

Identification of forces

First step in dealing with any problem in mechanics (free body diagram)

Free body diagram

Diagram of a body or group of bodies which is isolated from its environment and on which all external forces such as weight applied, forces, reactions, moments, and friction are applied

Moment

• A moment of a force provides a measure of the tendency of a force to cause an object to rotate about a point or axis

• Mathematically: M = Fd (scalar) or M = r x F

• Where M = moment, F = force creating the moment, d = perpendicular distance from line of action of force to moment center, r = position vector from moment center to force

Force

Push or pull. A, has magnitude, B, has direction, C, line of action

Parallelogram rule

Head to tail addition of vectors

Equilibrium

#1 concept, 2 chapters on it, sum of forces is zero

Moment

Tendency of a force to cause a rotation about a point or axis M = r x F; M = FD

Varignon's theorem

Can use the force or the component of a force to calculate the moment

Equivalence

All systems can be reduced to a single force and moment and in special situations can reduce to a single force at a known location

Transmisibility

Does not matter whether you push or pull as long as you maintain the same line of action; the result is the same

Lateral transfer theorem

Allows the movement of a force laterally (different line of action) as long as a moment (couple) is added

Newton's 3rd law

for every action there is an equal and opposite reaction

Super position

As long as there is linearity a complex problem can be broken down into simpler pieces and summed

Friction

coulombs laws of dry friction which are empirical in nature (not derived but observed)

Area moment of inertia

Stiffness parameter based on shape

Questions to ask

• Where did the equation come from?

• Does it have restrictions?

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