Lecture 6 -Vestibular Sense
VESTIBULAR SENSE
What is Vibration?
Originates from the Latin word "vibrare" meaning shaking or brandishing.
Defined as a mechanical phenomenon with oscillations occurring around an equilibrium point.
Describes the repetitive movement of an object: back/forward, right/left, or up/down.
Illustrated through a mass-spring system; when pulled down and released, it moves in a waveform pattern.
Equilibrium and Forced Vibration
Objects undergoing vibrational motion possess a resting position (equilibrium position) when not vibrating.
Applying force to an object disrupts its equilibrium, initiating vibration (forced vibration).
Without continuous forced vibration, energy dissipates, leading to a phenomenon called damping.
Damping refers to the loss of energy in a vibrating object over time.
Why Doesn't the Bobblehead Stop Immediately?
Governed by Newton's First Law of Motion; a restoring force acts to slow the bobblehead as it moves away from equilibrium.
Characteristics of periodic motion:
A vibrating object moves over the same path repeatedly; this regular repetitive motion is termed periodic motion.
Sinusoidal Nature of Vibration
Graphical Representation
The graph of a vibration displays a sine wave shape.
Periodicity
Vibrations exhibit a periodic nature, indicating consistent repetition over time.
Damping Characteristics
Damping indicates some energy loss as the vibration persists.
Key Measurements in Vibrational Motion
Period: Defined as the time taken for one complete cycle of motion (measured in seconds, milliseconds, etc.).
Frequency: The number of complete cycles in a given period, measured in cycles/second or Hertz (Hz).
Higher frequency corresponds to a lower period; frequency and period are reciprocals.
Measurements and Examples
Example: Clyde Harvey recorded 927 claps in one minute.
Calculated Period: 0.0647 seconds/cycle
Calculated Frequency: 15.45 Hz.
Amplitude
Defined as the maximum displacement from an object's resting position.
Types of Vibration
Free or Natural Vibration
Occurs without external forces acting on the body.
Initiated by an initial internal force (e.g., swinging a child on a swing or striking a tuning fork).
Forced Vibration
Results from external forces applied to a mechanical system (e.g., unbalanced washing machines, engine vibrations, or earthquakes).
Earthquake-Proof Vibration Equipment
Accelerometer:
High Frequency Transducer.
Measures the acceleration, velocity, and displacement of vibrating bodies.
Vibrometer/Vibration Meter:
Low Frequency Transducer.
Measures high frequency vibrations.
Proximity Probe:
Sensors measuring the distance variation between a shaft and its support bearing; often used in turbines and compressors.
Occupational Exposure to Vibration
HAV (Hand Arm Vibration): Caused by regular high-level exposure to handheld tools, risking nerve, muscle, and joint damage leading to HAVS (HAV Syndrome).
Raynaud’s Syndrome: A vascular disorder, narrowing blood vessels, resulting in symptoms like numbness and pain.
Carpal Tunnel Syndrome: Compression of median nerve in the wrist leading to pain and tingling.
WBV (Whole Body Vibration): Occurs through contact with vibrating surfaces; affects standing or sitting individuals.
Health Effects of Vibration
Includes inflammation of joints (e.g., tenosynovitis).
Fatigue poses safety risks, especially in transportation sectors.
Ways to Prevent Common Vibration Hazards
Anti-Vibration Tools: Reduce vibration levels (e.g., anti-vibration saws).
Anti-Vibration Gloves: Made of viscoelastic materials to minimize vibration exposure.
Safe Work Practices:
Use minimum grip strength for safety, take rest breaks, avoid faulty tools, and rest tools on workpieces when possible.
Employee Education: Training on proper tool use and maintenance to prevent unnecessary vibrational exposure.
Prevention Strategies
Engineering Controls: Tool redesign, vibration dampening.
Administration Controls: Implementing safer work protocols.
Personal Protective Equipment: Utilizing gloves and dampers.