Physics Definitions

moment of inertia

an object's tendency to resist angular acceleration; rotational equivalent to mass

force

any influence that causes an object to undergo a change in velocity

rigid body model

approximation of many real objects of practical interest

displacement

change in position

angular velocity

rate at which a particle's angular position is changing as it moves around a circle

power

rate at which energy is transferred or transformed

explosion

when a short but intense interaction causes two or more particles to move apart

Newton's Third Law

when one object exerts a force on another, the second object exerts a force on the first and the two create an action/reaction pair

work-kinetic energy theorem

when one or more forces act on a particle as it is displaced from an initial position to a final position, the net work done on the particle by these forces causes the particle's kinetic energy to change by ∆K=Wnet

collision

when two objects come together for a short but intense interaction

static equilibrium

zero velocity

centripetal acceleration

acceleration directed toward the center of the circle

impulse approximation

all external forces are negligible compared to the impulsive force

period

amount of time needed for a particle to go around a circle one time

massless string approximation

assumption that a string has zero mass

perfect pulley

assumption that the string is massless and pulley is frictionless

physics

branch of science concerned with matter and energy and the interaction between them

energy

capacity of a system to do work

motion

change in an object's position with respect to time

angular displacement

change in angle used to measure the particle's circular motion

acceleration

change of velocity with respect to time; rate of change of velocity vector

non-uniform circular motion

circular motion where the angular velocity is not constant; change in angular velocity is caused by a tangential acceleration

motion diagram

composite photo showing position of object for several moments in time

kinetic energy

energy associated with movement of objects

thermal energy

energy associated with system's temperature

energy transfer

energy exchange between system and environment

energy transformation

energy exchange within the system

equation of motion

equation that completely describes the motion of a system as a function of time

propulsion

force that a system with an internal source of energy uses to drive itself forward

contact force (spring, tension, normal, friction, drag, thrust)

force that acts on an object through physical contact

long range force

force that exerts no physical contact on an object

linear restoring force

force that is inversely related to the distance of the object from its equilibrium position

restoring force

force that returns a system to its equilibrium position

gravitational torque

found by treating the object as if all its mass were concentrated at the center of mass

impulse momentum theorem

impulse given to a particle changes that particle's momentum

impulsive force

large force exerted during a short time interval

pendulum

mass hanging distance L from pivot point

center of mass (cm)

mass-weighted center of an object

amplitude

maximum displacement from equilibrium

derivative

measure of how a function changes as its input changes

work

mechanical transfer of energy to or from a system by an external force

parallel axis theorem

moment of inertia about a parallel axis is the center of mass moment plus the moment of inertia of the entire object treated as a point mass at the center of mass; follows the principle of superposition

2-D kinematics

motion in two directions

uniform circular motion

motion in which a particle moves around a circle at a constant speed; angular velocity is uniform and constant

projectile motion

motion in which acceleration is only due to gravity

non-uniform motion

motion in which velocity is not constant

uniformly accelerated motion

motion occurring if and only if an object's acceleration is constant

periodic motion

motion that repeats itself after a well-defined time period

interaction

mutual influence of two objects on each other

principle of superposition

net force on an object is given by the vector summation of all individual forces

dynamic equilibrium

nonzero velocity

fictitious force

not a real force; no external force acting on an object, but can be used to describe motion

frequency

number of oscillations completed per second

Newton's Second Law

object of mass subjected to a force will undergo an acceleration (F=ma)

rotational motion

object rotates around a fixed point and every point on the object moves in a circle

rigid body

object whose size and shape don't change as it moves

elastic collision

objects collide then bounce apart

damped oscillation

oscillator that slows down and eventually stops

simple harmonic motion

oscillatory motion that is sinusoidal

trajectory

path followed by a projectile object

equilibrium position

position a system naturally assumes when there is no outside influence

phase

position in cycle of oscillation

vector

quantity described by magnitude and direction

scalar

quantity fully defined or described by single number

conservation

quantity that stays the same throughout an interaction

velocity

rate of change of position vector

oscillatory motion

repetitive back and forth motion of an object about an equilibrium position

angular momentum (L)

rotational analog to linear momentum

torque

rotational equivalent to force

instantaneous velocity

speed and direction of object at one instant in time

equilibrium

state of an object when the net force acting on an object is zero

potential energy

stored energy associated with the interaction and position of objects

uniform motion

straight line motion with equal displacement over successive equal-time intervals

dynamics

study of the cause of motion

integral

summation over infinitesimally small portions of the function

isolated system

system in which there are no net external forces

inertia

tendency of an object to resist a change in velocity

kinematics

the mathematical description of motion without regard to cause

period

time required to complete one cycle of oscillation

Law of Conservation of Mass

total mass in a closed system is constant

Law of Conservation of Momentum

total momentum during an interaction does not change; momentum is conserved for an isolated system

particle model

treats object as particle represented by a mass at a single point in space with no size or shape

perfectly inelastic collision

two objects stick together and move with a common final velocity

Newton's First Law (Law of Inertia)

velocity of an object will remain constant if and only if the net force acting on the object is zero

simple harmonic oscillator

vibrating object