Statics Of Rigid Bodies

Question 1

What is Mechanics?

Answer 1

A science that describes and predicts the conditions of rest and motion of bodies under the action of forces.

Question 2

What is a rigid body?

Answer 2

Many particles with fixed positions relative to one another.

Question 3

What are the subcategories of the mechanics of rigid bodies?

Answer 3

Statics and dynamics

Question 4

What does static mean?

Answer 4

The object is at rest.

Question 5

What does dynamic mean?

Answer 5

The object is in motion.

Question 6

Who started mechanics?

Answer 6

Mechanics goes back all the way to Aristotle and Archimedes but Newton was the one who laid the foundations.

Question 7

What acts as the basis of engineering science?

Answer 7

Newtonian mechanics.

Question 8

What are the basic concepts dealt with in mechanics?

Answer 8

Space, time, mass, force

Question 9

What is a particle?

Answer 9

A small amount of matter assumed to be a point.

Question 10

What is the parallelogram law for the addition of forces?

Answer 10

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.

Question 11

What is the principle of transmissibility and what are the conditions for this to hold true?

Answer 11

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.

Question 12

What is Newton’s 1st law?

Answer 12

Law of inertia- an object at rest stays at rest unless acted on by an imbalanced force.

Question 13

What is Newton’s 2nd law?

Answer 13

f=ma

Question 14

What is Newton’s 3rd law?

Answer 14

Forces and reactions between bodies in contact have the same magnitude, opposite sense and the same line of action.

Question 15

What is Newton’s Law of Gravitation?

Answer 15

2 particles are attracted to each other depending on their masses and distance from each other.

Question 16

Define a vector.

Answer 16

Mathematical expressions with both magnitude and direction.

Question 17

What things define a force?

Answer 17

Magnitude, direction, line of action, sense and point of application.

Question 18

What is a fixed vector?

Answer 18

A vector that can’t be moved without changing the problem.

Question 19

What are free vectors?

Answer 19

Vectors that can be moved around.

Question 20

What are equal vectors?

Answer 20

Same magnitude and direction

Question 21

Define moment.

Answer 21

Measure of the tendency of a body to rotate about a point or axis.

Question 22

What is the formula for moment?

Answer 22

Moment= force x distance

Question 23

Considering the properties of a force, when will moment exist?

Answer 23

When equal and opposite forces (same magnitude, opp. Direction) have different lines of action.

Question 24

What is the moment arm?

Answer 24

The perpendicular distance between the line of action of the force and the center of moments.

Question 25

Define center of moments.

Answer 25

The actual point about which the force causes rotation.

Question 26

Define couple.

Answer 26

2 equal and opposite force, parallel lines of action, produce rotation but not translation, separated by a perpendicular distance

Question 27

Define equilibrium.

Answer 27

State of balance between opposing forces.

Question 28

Describe an object in equilibrium with regards to spinning and accelerating.

Answer 28

Not spinning or accelerating.

Question 29

What's the mathematical condition for equilibrium?

Answer 29

0 force and moment in all dimensions

Question 30

A free body diagram shows all the _____ forces acting on a body.

Answer 30

External.

Question 31

Def. applied force.

Answer 31

Force exerted by another person or object.

Question 32

Def. gravity force.

Answer 32

Object's weight.

Question 33

Def. normal force.

Answer 33

Support force exerted on an object in contact with another stable object.

Question 34

Def. frictional force.

Answer 34

Force exerted by a surface as an object moves across it.

Question 35

What is the gravitational pull of a massive body on an object ?

Answer 35

Weight.

Question 36

Where is the force of an object assumed to be concentrated?

Answer 36

Center of gravity?

Question 37

What is the average position of all the particles of an object?

Answer 37

Center of mass.

Question 38

When does the center of gravity equal the center of mass?

Answer 38

When g is constant.

Question 39

What is the geometric center of an object?

Answer 39

Centroid.

Question 40

When does the center of mass equal the centroid?

Answer 40

When the object has constant density.

Question 41

What is a load?

Answer 41

A force applied to a structure

Question 42

What are the ways of describing a load?

Answer 42

Types, distribution, time, location and method of application.

Question 43

What are loads according to the types?

Answer 43

Dead, live, wind, earthquake, snow.

Question 44

What are the types of loads according to time?

Answer 44

Static, sustained, impact, cyclic.

Question 45

What are the types of loads according to distribution?

Answer 45

Concentrated, distributed

Question 46

Motion resisting forces at the supports of an object are called...

Answer 46

Reactions

Question 47

What is a normal reaction?

Answer 47

Reaction perpendicular to the contact support.

Question 48

What is a hinge reaction?

Answer 48

Reaction that resists horizontal and vertical motion but not rotation.

Question 49

What is a cantilever?

Answer 49

Resists both forces and moments. A beam supported on one end.

Question 50

What is friction?

Answer 50

A reaction that develops between sliding bodies.

Question 51

If the bodies only tend to slide, the friction is called...

Answer 51

Static

Question 52

The type of friction that develops between sliding bodies is called..

Answer 52

Dynamic friction.

Question 53

What do you call the state of motion when the object is about to slide?

Answer 53

State of impending motion.

Question 54

Static friction is directly proportional to the...

Answer 54

Normal force and relative roughness.

Question 55

A load that passes through the centroid of the resisting section

Answer 55

Centric/axial

Question 56

Load applied parallel to the cross section

Answer 56

Shearing

Question 57

Load that twists

Answer 57

Torsional

Question 58

Load that bends

Answer 58

Flexural

Question 59

What is stability?

Answer 59

Property of an object that causes it to develop actions that restore the original condition when disturbed from a condition of equilibrium.

Question 60

These are responses to small disturbances which restore equilibrium.

Answer 60

Stable equilibrium.

Question 61

What is overturning moment?

Answer 61

The moment that causes an object to tip over.

Question 62

What is the moment that restores an object to its original condition?

Answer 62

Restoring moment.

Question 63

The type of equilibrium where overturning moments develop.

Answer 63

Unstable equilibrium

Question 64

The type of equilibrium when the body is displaced and it stays in the new position.

Answer 64

Marginally stable equilibrium.

Question 65

Stable objects have...

Answer 65

Wide base, low center of gravity