Physics of Motion and Stability

Flashcards for reviewing key concepts in the physics of motion, stability, and lever systems.

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 (moment of force)

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 (moment arm or lever arm)

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

Angular Position

The location of a given point, defined by its distance from the origin and the angle between the chosen reference axis and the line formed by connecting the given point to the origin.

Angular Displacement

The change in angular position of a segment or any 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 entire interval over which it changed.

Stability

Refers to how much resistance a person can handle.

Balance

Ability to control forces that make a person stable.

Linear stability

Concern of a person moving in a particular direction.

Rotary stability

Concerned with a person who is rotating.

Frictional forces

Helps to increase stability.

Base of Support

Area on the ground enclosed with points of contact.

Equilibrium

The result when forces and net torque are equal to zero.

Machine

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

Lever System

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

Fulcrum

The axis around which a lever rotates.

Centripetal acceleration

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

Rotational Inertia (angular 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 its mass were concentrated at one point.

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.