Key Concepts in Mechanics

Vocabulary flashcards based on key concepts of mechanics, including forces, torque, stability, machines, and levers.

Centric force

A force having a line of action that passes through the center of mass of an object.

Eccentric force

A force having a line of action that does not pass through the center of mass of an object.

Torque

The tendency of an eccentric force to rotate an object around an axis.

Axis of Rotation

The point about which a body rotates.

Force Arm

The perpendicular distance between the axis of rotation and the line of action of the applied force.

Angular Position

The location of a point, defined by its distance r from the origin and the angle θ between the reference axis and the connection line.

Angular Displacement

The change in angular position of a segment or point on the rotating segment.

Radian

The ratio of the length of a circular arc to the length of the circle’s radius; 1 rad = 57.3°.

Radius of Rotation

The distance from the axis of rotation to a given point on the rotating segment.

Angular Velocity

The vector rate of angular motion, or rate of angular motion in a specific direction.

Tangential Linear Velocity

The linear velocity of a point on a rotating segment.

Angular acceleration

A change in magnitude or direction of the angular velocity vector with respect to time.

Average angular acceleration

The change in angular velocity divided by the time interval over which it changed.

Stability

The resistance of an object to having its equilibrium disturbed.

Balance

The ability to control the current state of equilibrium; implies conscious effort and coordination.

Linear stability

The resistance of a body to having its linear equilibrium disrupted.

Base of Support

The area formed by the points of contact with a resistive surface providing counterforce.

Equilibrium

A state where an object is either at rest or rotating with constant angular velocity.

Machine

An apparatus or system that uses the combined action of several parts to apply mechanical force.

Centripetal acceleration

An acceleration caused by a change in direction of the velocity vector; a center-seeking acceleration.

Rotational Inertia

The resistance of an object to having its state of angular motion changed.

Moment of Inertia

The mathematical relationship of mass, mass distribution, and rotational inertia.

Radius of Gyration

The distance that represents how far the mass of a rigid body would be from an axis of rotation if concentrated at one point.

Lever System

A machine consisting of a rigid or semi-rigid object capable of rotating about an axis.

Fulcrum

The axis around which a lever rotates.

Motive Torque

An eccentrically applied force that attempts to rotate a lever in a given direction about a fulcrum.

Resistive Torque

An eccentrically applied force that attempts to rotate a lever in a direction opposite that of the motive torque.

Effort Arm

The moment arm for the motive force.

Resistance Arm

The moment arm for the resistive force.

First class lever system

A lever system in which the fulcrum is between the motive and resistive forces.

Second class lever system

A lever system in which the resistive force is between the fulcrum and the motive force.

Third class lever system

A lever system in which the motive force is between the fulcrum and the resistive force.