Statics Of Rigid Bodies Flashcards
What is Mechanics?
A science that describes and predicts the conditions of rest and motion of bodies under the action of forces.
What is a rigid body?
Many particles with fixed positions relative to one another.
What are the subcategories of the mechanics of rigid bodies?
Statics and dynamics
What does static mean?
The object is at rest.
What does dynamic mean?
The object is in motion.
Who started mechanics?
Mechanics goes back all the way to Aristotle and Archimedes but Newton was the one who laid the foundations.
What acts as the basis of engineering science?
Newtonian mechanics.
What are the basic concepts dealt with in mechanics?
Space, time, mass, force
What is a particle?
A small amount of matter assumed to be a point.
What is the parallelogram law for the addition of forces?
2 forces acting on a particle can be replaced by a single resultant force which is the diagonal of the parallelogram made by the forces.
What is the principle of transmissibility and what are the conditions for this to hold true?
The conditions for equilibrium will not change if the force is applied at a different point on the body provided the force has the same magnitude, direction, line of action, and provided it is acting on a rigid body.
What is Newton’s 1st law?
Law of inertia- an object at rest stays at rest unless acted on by an imbalanced force.
What is Newton’s 2nd law?
f=ma
What is Newton’s 3rd law?
Forces and reactions between bodies in contact have the same magnitude, opposite sense and the same line of action.
What is Newton’s Law of Gravitation?
2 particles are attracted to each other depending on their masses and distance from each other.
Define a vector.
Mathematical expressions with both magnitude and direction.
What things define a force?
Magnitude, direction, line of action, sense and point of application.
What is a fixed vector?
A vector that can’t be moved without changing the problem.
What are free vectors?
Vectors that can be moved around.
What are equal vectors?
Same magnitude and direction
Define moment.
Measure of the tendency of a body to rotate about a point or axis.
What is the formula for moment?
Moment= force x distance
Considering the properties of a force, when will moment exist?
When equal and opposite forces (same magnitude, opp. Direction) have different lines of action.
What is the moment arm?
The perpendicular distance between the line of action of the force and the center of moments.
Define center of moments.
The actual point about which the force causes rotation.
Define couple.
2 equal and opposite force, parallel lines of action, produce rotation but not translation, separated by a perpendicular distance
Define equilibrium.
State of balance between opposing forces.
Describe an object in equilibrium with regards to spinning and accelerating.
Not spinning or accelerating.
What’s the mathematical condition for equilibrium?
0 force and moment in all dimensions
A free body diagram shows all the _____ forces acting on a body.
External.
Def. applied force.
Force exerted by another person or object.
Def. gravity force.
Object’s weight.
Def. normal force.
Support force exerted on an object in contact with another stable object.
Def. frictional force.
Force exerted by a surface as an object moves across it.
What is the gravitational pull of a massive body on an object ?
Weight.
Where is the force of an object assumed to be concentrated?
Center of gravity?
What is the average position of all the particles of an object?
Center of mass.
When does the center of gravity equal the center of mass?
When g is constant.
What is the geometric center of an object?
Centroid.
When does the center of mass equal the centroid?
When the object has constant density.
What is a load?
A force applied to a structure
What are the ways of describing a load?
Types, distribution, time, location and method of application.
What are loads according to the types?
Dead, live, wind, earthquake, snow.
What are the types of loads according to time?
Static, sustained, impact, cyclic.
What are the types of loads according to distribution?
Concentrated, distributed
Motion resisting forces at the supports of an object are called…
Reactions
What is a normal reaction?
Reaction perpendicular to the contact support.
What is a hinge reaction?
Reaction that resists horizontal and vertical motion but not rotation.
What is a cantilever?
Resists both forces and moments. A beam supported on one end.
What is friction?
A reaction that develops between sliding bodies.
If the bodies only tend to slide, the friction is called…
Static
The type of friction that develops between sliding bodies is called..
Dynamic friction.
What do you call the state of motion when the object is about to slide?
State of impending motion.
Static friction is directly proportional to the…
Normal force and relative roughness.
A load that passes through the centroid of the resisting section
Centric/axial
Load applied parallel to the cross section
Shearing
Load that twists
Torsional
Load that bends
Flexural
What is stability?
Property of an object that causes it to develop actions that restore the original condition when disturbed from a condition of equilibrium.
These are responses to small disturbances which restore equilibrium.
Stable equilibrium.
What is overturning moment?
The moment that causes an object to tip over.
What is the moment that restores an object to its original condition?
Restoring moment.
The type of equilibrium where overturning moments develop.
Unstable equilibrium
The type of equilibrium when the body is displaced and it stays in the new position.
Marginally stable equilibrium.
Stable objects have…
Wide base, low center of gravity
