AcousAcoustics (1)

Page 1: Collisions

Definition of Collisions
- Interaction between two or more particles over a short period where they exert strong forces on each other.
- Physical contact is not essential.
Types of Collisions
1. Elastic Collision
  - Both momentum and kinetic energy are conserved.
  - Involves only conservative forces.
  - Total energy remains conserved.
2. Inelastic Collision
  - Momentum is conserved, but kinetic energy is not.
  - Involves non-conservative forces.
  - Total energy of the system is conserved.
  - If the bodies stick together post-collision, it's perfectly inelastic.
Coefficient of Restitution (e)
- Ratio of relative velocity of separation after collision to velocity of approach before collision.
- Formula:
  - For perfectly elastic collisions, e = 1.
  - For perfectly inelastic collisions, e = 0.
  - For other collisions, 0 < e < 1.
One Dimensional (Head-On) Collision
- Velocities of colliding bodies along the same line.
- Equations for velocities after collision (elastic and inelastic cases).
  - Equal masses exchange velocities.
  - If one mass is heavy and at rest, the heavy mass remains at rest while the light mass rebounds.

Other One Dimensional Cases
- Heavy body colliding with a light body results in:
  - v1 = u1 and v2 = 2u1 if m1 >> m2.
Kinetic Energy Loss in Collisions
- For inelastic collision:
  - ΔE = m1m2 / (2(m1 + m2)) * (u1 - u2)^2 * (1 - e^2).
- For perfectly inelastic collision:
  - Loss of kinetic energy: m1m2(u1 - u2)^2 / (2(m1 + m2)).
Height After Inelastic Collisions
- Height related to rebound velocity after n collisions:
  - e_n = v_n / v_0 = √(h_n / h_0).

Two Dimensional (Oblique) Collision
- Velocities do not lie along the same line.
- Equations for conservation of momentum in horizontal and vertical directions.
Acoustics
- Sound as energy transmitted as pressure waves from vibrations.
- Branch of physics dealing with sound: acoustics.
  - Main application: enhance music/speech sound quality.
  - Studied by acousticians and acoustical engineers.

Environmental Acoustics
- Concerned with noise and vibration from transportation.
Musical Acoustics
- Study of the physics of music, vocal sounds, instruments, and therapy.
Ultrasounds
- Frequencies greater than human hearing limits; applied in various tech fields.
Infrasounds
- Frequencies below 20 Hz; applicable in geology and earthquake detection.

Vibration and Dynamics
- Study of mechanical systems and vibrations, applied in construction and railways.

Key Concepts
- Reverberation: sound persistence in halls due to reflections.
- Reverberation Time (T)
  - Time taken for sound intensity to fall to one-millionth (60 dB) of original level.
  - Optimum T: 1s for speech, 2s for music.

Good Acoustics Conditions
1. Adequate energy for syllable clarity.
2. Optimal reverberation time (1s for speech and 2s for music).
3. Uniform sound distribution throughout the hall.
4. Minimize external sound interference.
5. Avoid curved walls to prevent sound focusing.

Control of Reverberation Time
- Manage T by design choices, like window openings and surface coverings.
Recording Techniques
- Mechanical Recording: Stylus engraves disc patterns from sound.
- Optical Recording: Converting sound into electric impulses recorded on film.

Music Elements
- Pitch, rhythm, dynamics, timbre.
Noise vs. Musical Sound
- Musical sound: continuous vibrations; noise: irregular, unpleasant sounds.
Music Genres
- Divided into various classifications (e.g., popular, art music).

Roles in the Music Industry
- Songwriters, performers, sound engineers, event planners, etc.
Importance of Music
- In ceremonies, social events, and as a career.
Rhythm and Structure
- Arrangement of sounds; maps time through meters.

Types
- Porous, panel absorbers, resonators.
Porous Absorbers
- Carpets, fibrous materials that absorb sound through heat conversion.

Material Characteristics
- Good sound reflectors generally prevent sound transmission.

Acoustic Foam Benefits
- Affordable, easy to install, effective in reducing noise and improving acoustics across various settings.

Eco-Friendly Materials
- Resistant to mold/mildew, versatile installation options.
Acoustic Partitions
- Temporary solutions for dividing spaces; customizable.

Other Foam Types
- Packaging and shipping solutions; enhance soundproofing where needed.

EASYmass and EASYpanel
- Specific boards for effective sound insulation and absorption.