Chapter 13

Question 1

balance

Answer 1

a person’s ability to control equilibrium

Question 2

base of support

Answer 2

area bound by the outermost regions of contact between a body and support surface or surfaces.

Question 3

center of mass centroid center of gravity

Answer 3

point around which the mass and weight of a body are balanced, no matter how the body is positioned.

Question 4

couple

Answer 4

pair of equal, oppositely directed forces that act on opposite sides of an axis of rotation to produce torque.

Question 5

dynamic equalibrium (D’Alembert’s principle)

Answer 5

concept indicating a balance between applied forces and inertial forces for a body in motion.

Question 6

first-class lever

Answer 6

lever positioned with the applied force and the resistance on opposite sides of the axis of rotation.

Question 7

fulcrum

Answer 7

the point of support, or axis, about which a lever may be made to rotate.

Question 8

lever

Answer 8

a simple machine consisting of a relatively rigid, barlike body that may be made to rotate about an axis.

Question 9

mechanical advantage

Answer 9

ratio of force arm to resistance arm for a given lever.

Question 10

moment arm

Answer 10

shortest (perpendicular) distance between a force’s line of action and an axis of rotation.

Question 11

reaction board

Answer 11

specially constructed board for determining the center of gravity location of a body positioned on top of it.

Question 12

second-class lever

Answer 12

lever positioned with the resistance between the applied force and the fulcrum.

Question 13

segmental method

Answer 13

procedure for determining total-body center of mass location based on the masses and center of mass locations of the individual body segments.

Question 14

stability

Answer 14

resistance to disruption of equilibrium.

Question 15

static equilibrium

Answer 15

motionless state characterized by sumSF(V)=0, sumSF(h)=0, and sumST=0.

Question 16

third-class lever

Answer 16

lever positioned with the applied force between the fulcrum and the resistance.

Question 17

torque

Answer 17

the rotary effect of a force about an axis of rotation, measured as the product of the force and the perpendicular distance between the force’s line of action and the axis.