# Glossary of Terms

Acceleration
Acceleration is a vector quantity that specifies the time rate of change of velocity.
Amplitude
Amplitude is the maximum value of a sinusoidal quantity (i.e. acceleration, displacement).
Center of Gravity
The point of support at which a body would be in balance.
Damping
Damping is dissipation of energy in an oscillating system. Limits maximum amplitude at isolator natural frequency.
A decade is the interval between two discrete frequencies having a basic frequency ratio of ten. For example, frequencies of 7 Hz and 70 Hz are said to be one decade apart.
Deflection
Deflection is the distance an elastic body or spring moves when subjected to a static or dynamic force. Typical units are inches or mm.
Displacement
Displacement is the change of position of a body, usually measured form the mean position of rest. Common units are inches (double amplitude) or mm (double amplitude). Displacement is related to acceleration by frequency.
Elastomer
A generic term which encompasses all types of rubber, natural or synthetic. There are numerous families of elastomers. The type of elastomer chosen for any application depends on the environment in which the elastomer will be used.
Forced Vibration
Forced vibration is the vibration resulting from the application of an external periodic force.
Foundation (Support)
A foundation is a structure that supports the gravity load of a mechanical system.
Fragility
Fragility is the amount of shock or vibration which a piece of equipment can withstand. Isolation systems are designed or selected to limit the transmission of forces to the stated fragility.
Free Vibration
Free vibration is the periodic motion occurring when an elastic system is displaced from its equilibrium position.
Frequency
Frequency is the number of times the motion repeats itself per unit of time. (The unit cycle per second is called Hertz (Hz.))
Isolation
Isolation is a reduction in the capacity of a system to respond to an excitation. This is attained by the use of a resilient element between the equipment and mounting surface.
Mass
Weight in pounds divided by the gravitational constant, (g=32.2ft/sec2 or 386 in/sec2)
Natural Frequency
Natural frequency is defined as the number of cycles of oscillation that occurs in a time period when moved from its normal position and allowed to vibrate freely.
Octave Band
An octave is the interval between two discrete frequencies having a frequency ratio of two. For instance, frequencies of 25 Hz and 50 Hz are said to be separated by one octave.
Periodic Motion
Periodic motion is a motion that repeats itself at definite intervals of time.
Random Vibration
Random vibration is vibration whose magnitude is not specified for any given instant of time.
Resonance
Resonance occurs when the frequency of excitation is equal to the natural frequency of the system. When this happens, the amplitude of vibration increases and is only limited by the amount of damping present in the isolation system.
Resonant Frequency
Resonant frequency is a frequency at which resonance exists.
Shock
Shock is a transient condition where the equilibrium of a system is disrupted by a sudden applied force or increment of force, or by a sudden change in the direction or magnitude of a velocity vector.
Shock Absorber
A shock absorber is a device which dissipates energy to modify the response of a mechanical system to applied shock.
Shock Isolator (Mount)
A shock isolator is a resilient support that tends to isolate a system from shock motion (excitation).
Shock Pulse
A primary disturbance characterized by a rise and decay of acceleration in a relatively short time. Shock pulse is generally shown as a plot of acceleration vs. time.
Sinusoidal Vibration
Oscillations in which motion is periodic with time in the form of a sine curve. Rotating equipment generate vibrations which are frequently considered as sinusoidal.
Spring Rate/Stiffness
The force required to deflect an isolator a unit distance. Stiffness is the slope of a curve showing force on the Y-axis and deflection on the X-axis. Typical units are pounds/inch.